The Ultimate Buying Guide
Duplex filter and strainers play an integral role in oil.
Duplex Filter and Strainer Definition
Duplex Filter Working Principle and Functions
Types of Duplex Filters
Duplex Filter Assembly and Parts
The Complete Guide on How to Install a Duplex Filter
Duplex Filter Design and Drawing
Duplex Filter Advantage
How to Test a Duplex Filter
Factors That Affect Duplex Filters Service Life
Duplex Filter Maintenance Guide
Duplex Filters and Strainers Applications
How to Choose a Perfect Duplex Filter for Your Industry
Top 10 Duplex Filters and Strainers Manufacturer in Global Market
Attaining the highest degree of cleanliness as per the ISO …
Duplex filter and strainers play an integral role in oil, water or fuel piping systems. They remove coarse and fine contaminants that can jeopardize the normal operation of hydraulic systems. The design of duplex filters ensures uninterrupted or continuous flow in hydraulic systems.
The design of duplex filters ensures uninterrupted or continuous flow in hydraulic systems.
In this duplex filter and strainer eBook, you’re going to learn all the fundamental aspects about this vital accessory.
Now, let’s go straight to the main subject of this eBook
Duplex Filter and Strainer Definition
For you to understand what I am about to discuss here, it is important to know how a duplex strainer looks like.
Below, you can see both the 3D and technical drawing of a duplex filter assembly.
The similarities between the different types of duplex filter systems
The similarities between the real model and technical drawings are quite evident. I will discuss more about this in Chapter 6.
This chapter focuses on the duplex filter design and drawing.
Now, let me take you straight to this:
What is Duplex Filter?
Duplex filters are mechanical or electromechanical equipment with screen elements that removes or filter contaminants from a hydraulic system.
Basically, this is a closed pressure vessel with filters that remove Unlike the simplex filters where there is only one filter particles in the hydraulic systems. By doing so, it protects all hydraulic components downstream such as pumps, valves or any other machines.
Normally, these screen elements (filters) are removable and they come in different shapes and sizes. You will learn more about this in Chapter 4.
At times, you may refer to it as either a twin basket strainer or duplex strainer.
Why do we use the word “Duplex” ?
When you look at the duplex strainer diagrams above, they are basically two simplex filters. That is, one side is simply a replica of the other.
Parts and components of duplex oil filter assembly. Image source: Machinery Spaces
Unlike the simplex filters where there is only one filter chamber, here we have two.
Therefore, to connect these two filter chambers, we need a 3-way valve. Again, like the simplex filters, duplex filter have an inlet and an outlet.
This does not imply that a duplex oil filter assembly must have only a 3-way valve.
No, that is not true.
There are so many hydraulic valve technologies you can implement to ensure a duplex filter meets specific application requirements. Good examples are the custom oil filtration systems that may have four butterfly valves.
Irrespective of the valve type, they will still perform the same task – diverting flow from the input to any of the two filter baskets.
With this information, we can learn how a duplex strainer works. This leads us to our next chapter:
Duplex Filter Working Principle and Functions
In this section, you are going to learn how a duplex filter works. Irrespective of the duplex filter design, the working principle still remains the same.
From chapter 1, it is clear that a duplex filter:
When you look at the duplex strainer diagrams above, they are basically two simplex filters. That is, one side is simply a replica of the other.
So, how is this possible?
Installing the Duplex Filter
First, you must install the duplex filter appropriately. That is, you must take care of all the necessary precautions and it should be free from any form of vibrations.
You will learn more about how to install a duplex filter in Chapter 5.
Once you install the duplex filter assembly, contaminated hydraulic fluid will enter this system then leave when clean.
This is what happens:
Hydraulic Fluid Enters in Inlet of the Duplex Filter
Oil, water or any other hydraulic fluid will enter the duplex strainer through the inlet port. Depending on the position of the valve, it will flow down through one of the strainer basket.
Remember, the design of duplex filter assembly is such that, there is a valve that blocks the path through which the fluid flows to the strainer baskets.
Now, with the lever handle that controls the valve on one end, all fluids from the inlet will flow in the first strainer basket.
As the water passes through the first strainer, the filter element will trap all the contaminants. This implies that, only clean water will leave the strainer basket to the outlet port and pipe systems.
It is important to note that the basketfilter element plays an integral role in the duplex filter assembly. Therefore, it is critical to choose a material that is wear resistant and guarantee a long service life.
Therefore, you must consider the:
Remember, it is this filter element that will trap and hold all dirt.
Also, the duplex filter has a bypass valve you can use to protect the filter element during start up.
As the fluid continues to flow through the first strainer basket, the clogging indicator monitors the state of the filter element. Once the pressure drop goes beyond the set limit, the clogging indicator will show that the filter element is clogged.
Of course, it does this by comparing the output and input pressure in the two pipe systems.
As a result the operator can push the valve lever to the opposite end. By doing so, it will close the clogged basket strainer and open the one that was not in use.
So, instead of shutting down the entire system, you will continue to use the other filter elements.
Meanwhile, here is what you will do:
Clean the Clogged Duplex Filter Element
After closing the valve preventing back flow to the clogged filter housing assembly, you should deep pressurize and drain the housing.
You can do this by using the drain plugs. It will help you to dump the hydraulic fluid before you begin the cleaning process.
Remember, it is these drain plugs that help to keep the working area clean.
You can then remove the cover of the duplex strainer basket and pull out the filter element for cleaning. Furthermore, you can examine the filter element, whether it needs full replacement or not.
Replace the filter element back to the basket strainer and install the upper cap. Before you return the basket to a standby position, ensure you purge all air using the bleed valve.
Again, you can continue to operate your system until the clogging indicator turns on.
You can the turn the valve lever back to the original position. By doing so, you will use the standby basket as you service the clogged one and the cycle continues.
Clearly, the working principle of duplex filter assembly is quite simple.
With these in mind, now let me summarize the functions of duplex filter assembly. You will learn about the key applications later in Chapter 11.
Keep reading to learn more fundamental aspects of this hydraulic fluid purification system.
Functions of Duplex Filter Assembly
The main function of duplex filter assembly is to remove both large and small particles (contaminants) in hydraulic system. Normally, the type contaminants this oil purification system can remove depends on the pores of the filter element.
By design, their function is to ensure that the purification or treatment process is in continuous mode/without any interruptions.
Apart from these, duplex filters have a large filtration area. Therefore, it guarantees a high filtration capacity and the pressure drop is minimal.
Again, the good thing is that all these contaminants will remain in the strainer basket. Normally, the contaminated fluid enters the basket strainer from the inside and leaves to the outside surface.
Now that you know the duplex filter working principle and function, let’s proceed to another important aspect. This is critical whenever you want to buy a new oil filtration machine for a hydraulic system.
Types of Duplex Filters
As you will see in this chapter, the mode of classifying duplex filters depends on numerous factors. These may include temperature, pressure, fabrication process or material.
For the scope of this eBook, the main focus will be on 5 different types of duplex filters:
Also, this section will cover the custom duplex filters.
Generally, these are the most common types of duplex filters that are available in the market.
Let’s review the fundamental aspects of these duplex filter systems.
3.1 High Pressure Duplex Filter
The design of these duplex filters is such that they can withstand extremely high pressure. In most cases, they have a compact design that can withstand up to 32Mp.
High pressure duplex filters are made from carbon steel and stainless steel. However, the duplex filter manufacturers may also opt for other materials depending on application requirements.
Below is an example of a high pressure duplex filter:
Irrespective of the high pressure duplex filter design, this accessory should meet certain specifications. Below are critical aspects you should know:
3.1.1 Technical Specifications of High Pressure Duplex Filter
Whenever you’re planning to buy a high pressure duplex filter, it is important to consider technical specifications. Through this, you can tell whether duplex strainer is suitable for a specific application or not.
Here are key specifications to consider:
- Filtration; the filter fineness can range between 3 and 100 µm
- Pressure; maximum is 32Mpa with a pressure loss of ≤0.5
- Flow rate; depending on the design, flow rate may range from 30 to over 660 liters/minute.
- Diameter; the diameter may vary from 20 to over 50 mm depending on the duplex filter model.
- Operating temperature; the fluid temperature may range from 0°C to 105°C. Remember, this may vary depending on the application at hand.
Apart from these, you need to check the connection type. Quite a number of high pressure duplex filters have flange connection.
3.1.2 Advantages of High Pressure Duplex Filter
Below are the top 6 advantages of high pressure duplex filters you need to know:
- Most designs allow for faster part changeover, cleaning and repair
- Guarantees uninterrupted flow
- Easy to operate
- Fits a wide range of applications such as mechanical hydraulic control, gear-box, lube systems, etc.
3.1.3 Disadvantages of High Pressure Duplex Filter
Some of the main disadvantages of duplex filters include:
- Requires a robust construction and design that may be expensive
- Production time may be long
I know you may use duplex filter systems for low or medium pressure applications. However, it will only make economic sense if you use them for the purpose they were designed for.
Otherwise, you can consider other options such as the medium pressure duplex filter.
3.2 Medium Pressure Duplex Filter
Unlike the high pressure duplex filter, the design of these systems can only handle moderate pressure. You will find that quite a number of medium pressure duplex filters have a maximum working pressure of 21Mpa.
Again, the design, structure, features and type of material will depend on the specific application at hand.
Below is an example of a medium pressure duplex filter:
With these in mind, let’s review critical aspects of this oil filtration system.
3.2.1 Technical Specification of Medium Pressure Duplex Filter
Before you buy a medium pressure duplex filter, it is important to consider its unique specifications. This way, you can customize the duplex oil filter assembly for specialized applications.
Here are features unique to medium pressure duplex filter:
- Mostly feature thread connection system.
- Made from cast steel thou other material options are available depending on specific applications.
- Maximum pressure is 21Mpa with pressure loss varying from ≤0.1 to 0.35Mpa.
- Flow rate may vary from 160 to 660 liters/minute.
- Filtration varies from 3 to 200µm.
It’s from these specifications that you will choose whether an oil filtration machine meets your unique specific applications or not.
3.2.2 Advantages of Medium Pressure Duplex Filter
In industrial oil filters, these accessories offer the following key advantages:
- Continuous operation even during element change.
- Compact and lightweight.
- Easy to change filter element.
- Good sealing with a ball valve.
- Easy to operate.
3.2.3 Disadvantages of Medium Pressure Duplex Filter
Like other duplex filter systems, these oil purification systems have the following main disadvantages:
- Production time may be long, especially for complex designs.
- Achieving “zero leakage” can be cumbersome with a wrong design.
Apart from these two, for low pressure purification systems, you can opt for:
3.3 Low Pressure Duplex Filter
The structural design of low pressure duplex filters is slightly different from the other two. It is specifically designed for low pressure applications.
Low pressure duplex filters are made from either carbon steel or stainless steel. This will depend on the application.
Again, depending on the specific applications, they may have unique designs and finishing. Where, the surface may be treated with phosphorous or painted with polyurethane.
Like other oil purification systems, you need to be clear about the technical specifications of low pressure duplex filters. Below are a few factors you need to specify.
3.3.1 Technical Specification of Low Pressure Duplex Filter
Below are fundamental aspects you need to specify:
- Flow rate; they may vary from 25 to over 15000 liters/minute.
- Filtration; this may vary from 3 to 100 µm.
- Working pressure is 1.6Mpa with a ≤0.35 pressure loss.
- Bypass pressure setting is 0.4Mpa
- Working temperature
Generally, the modern low pressure duplex filters combine a high capacity with low pressure drops.
Again, as you order for a low pressure duplex filter, you should note that it has both advantages and disadvantages.
3.3.2 Advantages of Low Pressure Duplex Filter
As you shop for these industrial oil filters, it is important to note that they have the following key advantages:
- Provide simple and cost effective way of removing impurities.
- Guarantee continuous operation.
- Bleed valves provide smooth change over.
- Many connection options.
- Compact and lightweight.
3.3.3 Disadvantages of Low Pressure Duplex Filter
The main disadvantages of low pressure oil filtration machine may vary depending on the manufacturer. For instance, you should take note of the following:
- Improper designs may cause leakages
- Limited pressure output
At times, you may need special duplex filters for your oil filtration systems. In such situations, you will need either cast or welded duplex filters.
Let’s see what is so unique about these oil filtration machines.
3.4 Welded Duplex Filter
They are a perfect inline filters in situations where operations cannot be suspended during maintenance.
Depending on the specific applications at hand, the welded duplex filters are made of carbon steel or stainless structure. The duplex filter design is such that it is easy to switch the housing.
Even as you shop for a suitable welded duplex filter, the technical specifications still play an integral role.
Below are the general specifications you should know.
3.4.1 Technical Specifications of a Welded Duplex Filter
Some of the main features that make this oil filtration system unique include:
- “Zero leakage” within the flange joints
- Housing designs conform to the ASME codes
- Welded duplex filter in the turbo compressor market feature a double screen synthetic medium
- Flow rate and pressure vary depending on the design
- Reduced leak points
Apart from these, you should also consider the rate of filtration, possible pressure loss and connection type. With these, you can easily choose a welded duplex filter that meets the specific needs of your applications.
Now, let us have a quick overview of the advantages and disadvantages of these oil purification systems.
3.4.2 Advantages of Welded Duplex Filter
Like the other duplex strainers, these oil filtration systems have the following key advantages:
- Flexible and alterable design, thus, can easily be adapted to most hydraulic systems
- Lightweight design
- Easy to customize inlet and outlet direction
- Small and compact design, hence requires small installation space
- Many connection types
3.4.3 Disadvantages of Welded Duplex Filter
Again, whenever you opt for welded duplex filters, you should note that it has the following disadvantages:
- Welding process is cumbersome hence long production time.
- High cost due to the designing process.
- It may have a limited output.
In case you need an oil filtration machine for specialized applications, another equipment to consider is the:
3.5 Cast Duplex Filter
If you are looking for same size duplex filter in large amounts, then it is time to try casted duplex filters. These may include cast aluminium, iron, steel.
The choice of material will depend on the type of application at hand.
In most cases, you will find duplex filters with a cast iron body and cover. However, the basket or filter element is made from stainless steel.
Furthermore, the cast duplex filters may incorporate stainless steel ball valves, with PTFE seals, which guarantee a tight shutoff.
With this, the cast duplex filter eliminates possible problems common in particulate sanction conditions.
3.5.1 Technical Specifications of Cast Duplex Filter
Below are important specifications of a duplex filter you should know:
- Type of material where steel, aluminium and iron are the most common
- Working pressure and temperature that may also vary
- Appropriate valve for easy changeover from online to standby
- Positive sealing
- Large filtration area
- Varying mesh and aperture sizes
3.5.2 Advantages of Cast Duplex Filter
At times, you may opt for casting duplex filters as opposed to other manufacturing processes. This is because it offers the following key benefits:
- Low cost production
- Casting is suitable for mass production of duplex filters
- Fast production of duplex filters
3.5.3 Disadvantages of Cast Duplex Filter
In most cases, casted duplex filters have the following disadvantages:
- They are unwieldy
- Difficulty in applying treatment on the surface
- Prone to leaking
- Easily forms pores of air holes during the production process
- Available only in small sizes and cannot handle high flow
Apart from these, at times you may opt for custom duplex filters.
Basically, the idea here is to customize nearly all specifications of the duplex filter. Therefore, the duplex filter manufacturer may change the following features:
- Diameter of the piping system and baskets
- Fluid flow rate
- Filtration capability
- Pressure; these include minimum, maximum and losses
- Connection type
- Type of material
- Surface treatment
- Size (overall size of the duplex filter)
In short, you can change as many specifications as possible.
With all these in mind, it is now time to explore the duplex filter assembly in details. You will learn about every part of this filtration equipment.
The chapter will give more insights on the technical specifications of this accessory. It will act as a basic introduction to choosing a perfect duplex filter for your industry.
You will learn more about the process in Chapter 12.
Duplex Filter Assembly and Parts
An oil filtration system is an assembly of different components and parts that eliminate contaminants in hydraulic systems.
The number of parts may vary depending on the type of oil filtering machine.
So, in this section, you are going to learn about different parts of industrial oil filters. Normally, these sections are visible when you analyze a technical drawing of the duplex filter.
As you can see, there are many parts and components here. However, to make it easy for you to understand, the focus will be on the following:
- Design and construction of the housing
- Filter cartridge and element
- Transfer valve
- Filter bypass valve
Let’s go straight to the main subject of this chapter:
4.1 Duplex Filter Housing
Duplex filter housing is a critical part that hosts all components of an oil purification system. Below, is a good example of a duplex filter housing made from stainless steel.
Now, what makes up duplex filter housing?
Type of Material
Depending on your unique application, you may choose stainless steel, iron, aluminum, bronze, etc.
Remember, it is the properties of a fluid that will determine the type of material you will choose for the overall design and structure of the duplex filter housing.
I believe this is quite straightforward. For example, the filter housing above is a stainless steel.
Inlet and Outlet
The filter housing hosts the inlet and outlet ports. In most cases, the inlet port is in the upper section while the outlet on the lower part.
In some designs, you may have the inlet and outlet ports on the two opposite sides of the duplex filter housing.
Drain plug plays an important role in duplex filter changeover procedure. For instance, you will use the drain plug to remove dirt or particles to keep the working area clean.
Furthermore, duplex filter housing has a vent plug. Through this, you can efficiently purge air to maintain pressure equilibrium.
A good duplex filter housing should have secure and stable installation platforms. This will prevent any form of vibrations when the fluid is passing through the duplex filter housing.
Most duplex filter housings have holes for fastening the entire system on an installation platform.
Apart from these fundamental aspects, you should consider:
- Covers; it should be one that is easy to remove and provides secure sealing
- Sealing mechanisms; O-rings are popular for this application
- Easy to operate lever handle; for changing the duplex filter housing
Again, as you look at the examples of duplex filter housings in this section, you will realize that they are parts joined together either through welding or using bolts.
Therefore, whenever you’re planning to buy a duplex filter assembly, ensure they are of high quality – guarantee “zero leakage”.
Another integral part of the duplex filter assembly is the:
4.2 Duplex Filter Cartridge
A duplex filter cartridge is the heart of an oil purification system.
Since the 1960s, cartridge filter technology has proved to be an economical and a versatile filtration process in the industry.
Quite a number of cartridges in the duplex filter systems have a cylindrical shape. Of course, this is due to the shape of the duplex filter housing.
In most cases the design of a duplex filter cartridge will depend on:
- Viscosity of the liquid
- Filtration efficiency and accuracy
- Dirt holding capacity
- Duplex filter housing
- Working medium
Once you have this information, you can confidently choose the best duplex filter cartridge.
Normally, cartridge filters are suitable for hydraulic systems where the contamination levels are less than 100 ppm. But this will depend on the design and type of the filter element.
Broadly, you can classify these duplex filter cartridges as:
Depth type duplex filter cartridge: Such a filter depends on the total thickness of a medium to remove contaminants or particles.
Surface type duplex filter cartridge: Filters are made from woven wire, clothes or paper like materials. The surface of the filter blocks particles or contaminants.
It is therefore important to be specific on the types of applications and duplex filters you need for an oil filtration system.
How to Increase Service Lifespan of Duplex Filter Cartridge
There are many ways through which duplex filter manufacturers increase the lifespan of a filter cartridge.
Here are a few design features of duplex filters that will increase the lifespan of a filter element:
- A bypass valve acts as a pressure relief thereby protecting filter element
- An alarm system protects the filter element by detecting when it is clogged
- Drain valve removes polluted oil, thereby protecting filter element
- Increasing size of filter surface; this allows for higher flows. Remember, this will also increase the dirt holding capacity
In duplex filter systems, some of the most common cartridges include:
a) Stainless Steel Filter Cartridge
These are some of the most common types of cartridges in duplex filters. Depending on the nature of the application, they come in either 304 or 316 stainless steel.
Furthermore, they come in either weave wire mesh or sintered fiber as a filter medium.
Their lengths may vary from 10” to 40” with filter micron rating being 1µm to 100µm. This will depend on the duplex filter housing design and the nature of the application at hand.
b) Carbon Filter Cartridge
In case you cannot afford the stainless steel filter cartridge, the carbon type can be a better alternative. It is one of those filters approved by the FDA for food service and water treatment applications.
These filters are mainly available in 5µm rating though the length varies from 10” 10 40”.
Other types of cartridge filters include polypropylene, membrane, microfiber glass and oil adsorption filters, just to mention a few.
In short, always be sure to get the best filter elements available in the market.
Another critical part of the duplex strainer is the:
4.3 Duplex Filter Transfer Valve
Duplex filter transfer valves play an integral role in oil purification systems.
For instance, a duplex filter may have transfer valves welded between the filter housing to ensure “zero leakage”.
Furthermore, transfer or diverter valves ensure a positive sealing, which guarantees uninterrupted and low pressure drop in duplex filter systems. It can direct flow into any of the two basket strainers independently.
All you need is switching lever to ensure smooth and efficient transition of flow.
Depending on the complexity of the duplex filter assembly design or an application at hand, you may have different designs of hydraulic valves.
That is, you may have a 3-way ball valve or a 6-way transfer valve system. The duplex filter manufacturer can choose any valve as long as it ensures smooth changeover.
Now, let’s review the different structures of change over valves for duplex filter assembly.
4.3.1 Different Structures of Duplex Changeover Valves
In this section, you’re going to learn about different types of hydraulic valves that are common in duplex filters.
As you shop for oil purification equipment, it is important to consider one with a good sealing. Remember, leakages may result in a significant pressure drop that may compromise the overall performance of a duplex filter.
Even during a duplex filter changeover procedure, the integrity of a valve plays a critical role.
Below are some of the most common valves you may consider in duplex filter design:
4.3.2 2-position 6-way valve
This is basically a directional control valve. By pushing the lever to a certain position, it will direct the fluid to an appropriate duplex filter basket.
The normal design of 2-position 6-way valve is such that it has:
- Valve housing
- A control spool
- Return spring
The structure is this duplex changeover valve is such that it connects two inlets and diverts the fluid to any of the four outlets.
Structure of a 2-position 6-way valve
4.3.3 Ball Valves
In duplex filter assemblies, these are 3 way ball valves that offer better sealing. From the image below, you can see all the vital components of the ball valves.
A structure of duplex filter with a ball valve
As you can see, the ball valves connect the two duplex filter housings. However, to improve their efficiency, it is important to integrate the valve with a pressure compensation feature.
In such systems, it acts as a changeover valve. Apart from these two, other duplex filter manufacturers may opt for:
- Cone valve
- Butterfly valve
- Cam valve
In short, it is upon the manufacturer to evaluate all the prevailing conditions to choose of hydraulic valves that ensure smooth and seamless transition. This is critical whenever you’re switching from one duplex basket to another.
Again, it is important to note that ball and directional valves are common in many duplex filter designs.
This is because they offer good sealing hence, ensuring efficiency and reliability.
With an efficient sealing effect, you don’t have to go through expensive hydraulic system shutdown.
4.4 Balance Valve
A balance valve plays an integral role during the duplex filter changeover procedure. Under normal circumstances, as the 3-way valve allows for smooth and seamless changeover, it must not compromise on the system performance.
It is during this stage that you need to equalize the built-in pressure in the duplex filter housing.
An example of a pressure balance valve in hydraulic system
Basically, it acts as a pressure relief valve, allowing for a smooth changeover whenever you want to change filter elements.
Apart from this, let’s discuss another critical component of oil filtering machines.
4.5 Duplex Filter Bypass Valve
A duplex filter must have a bypass valve. This is because it protects the duplex filter element from over pressurization and during start up.
Below is a video showing a how an engine oil bypass filter valve works.
Normally, as the differential pressure increases, it will eventually damage the filter elements. Therefore, without a bypass valve, your system is likely to damage the filter element.
The duplex filter manufacturers install bypass valves in the direction of the oil inlet. This valve will automatically open whenever the differential pressure goes beyond a set limit.
As a result, it protects filter element from bursting or collapsing when loaded with contaminants. Remember, an increase in differential pressure is due to the buildup in contaminants.
At times, incorporating a duplex filter bypass valve in an oil filtering machines may require further adjustments in the systems. Let’s review some of the most common and viable options:
Incorporating a Bypass Tank
This will prevent the unfiltered fluid from going into the system. Therefore, the unfiltered fluid will flow to a tank through a third port.
Basically, in this case, it will be a bypass to tank.
Blocked or No Bypass
With this option, there is no unfiltered fluid that will flow downstream. However, in such situations, the duplex filter assembly must have a filter element with higher collapse strength.
Furthermore, you should note that at any given time, the element should be able to withstand the differential pressure whenever the bypass valve opens. Therefore, it is important to select a bypass valve setting before sizing the duplex filter housing.
Apart from the duplex filter bypass valve, another critical component of duplex filter is the:
4.6 Duplex Filter Indicator
As you have seen from the previous examples, the filter elements of oil filtration systems are enclosed in a duplex filter housing. Therefore, you cannot see whether the filter element is clogged or not.
It is for this reason that a good oil purification system must have a duplex filter indicator.
With a clogging indicator, you can tell when to change the duplex filter elements. It monitors the filter elements by comparing the pressure difference between the input and output ports.
Through this, it relays an appropriate signal that will show you when to change the filter element.
Currently, there are many types of filter elements with the most common designs being either optical or electronic clogging indicators. At times, you may use a combination of the two.
You should ensure that the duplex filter indicator is set properly to avoid unnecessary errors.
Now that you the various parts of duplex filters, let’s move to yet another important segment of this eBook. This is where you will learn how to install duplex filters.
The Complete Guide on How to Install a Duplex Filter
This chapter covers all the necessary steps you need to follow when installing a duplex filter assembly. It is a systematic process that requires much attention.
Failure to follow any of the duplex filter installation process may be catastrophic to the entire system. In such situations, it may be difficult to achieve the ISO cleanliness standards and this may affect hydraulic systems.
Since I don’t want you to go along that route, let me show you how to install a duplex filter:
This is seawater duplex strainer. Image source: TPUB
5.1 Attention: Consider the Following before the Installation Process
Even before you begin to install an oil purification system, it is important that you consider the following:
First, you must have all the necessary safety gear. These may include boots, gloves, helmets, overall, safety boots or any other accessory that will protect you from possible injury.
Second, verify the specifications of the duplex filter assembly. You will get all these specifications on the nameplate.
Third, as you unpack the duplex filter, you should check if there are any damages on the machine that may have occurred during shipping. In case there is any, contact the duplex filter manufacturer.
Forth, you need to verify all the technical specifications of the duplex filter. These will include pressure rating, flow rate, temperature, filtration capacity, etc.
The specification of the machine will depend on the design, type and nature of the application at hand. You can review Chapter 3 of this eBook.
Fifth, you should ensure the every component of the duplex filter is compatible with the application you need it for. That is, you should check chemical compatibility and more importantly, evaluate the duplex filter material.
In short, it is important to do a comprehensive inspection of the duplex filter assembly. You should ensure everything is in the right place and the condition that the manufacturer has specified in the technical manual.
After doing all these, you can begin the installation process.
5.2 How to Install Duplex Filter Assembly
By following the steps I am going to highlight below, you can install the duplex filter without having prior experience. Here is all you need to do:
5.2.1 Prepare Where You Intend to Install the Duplex Filter
First, you should ensure that there is enough space around the duplex filter. That is, you need enough space for duplex filter changeover procedure.
You will learn more about duplex filter maintenance process in Chapter 10.
Remember, the main aim for installing a duplex filter is to ensure uninterrupted flow. This implies that, you will be replacing the filter basket when the system will be operating.
Therefore, you need enough space for your safety too. This is critical when you’re dealing with hydraulic systems that can emit unpleasant gases.
Second, prepare the platform where you intend to install the duplex filter. If possible, it should have all the necessary reinforcements.
As you prepare where you intend to install the duplex filter, you should use the technical drawing to have accurate measurements.
Again, you will also learn more about the duplex filter design and drawing in Chapter 6.
5.2.2 Fix the Duplex Filter Assembly
You should ensure that the piping system is in place and provide all the necessary support. Remember, you must not use the duplex filter assembly as a support.
For example, you can use expansion joints to prevent thermal expansions. With this, even the fluctuations in the piping system undermine the overall performance of the duplex filter strainer.
Also, using the duplex filter strainer as a support may cause misalignments that will eventually cause leakages.
So, with the piping system in place, make a steel pad or a concrete platform where you will install the duplex filter.
Now, you can lift the duplex filter using a suitable hoist mechanism or forklift. Place it on the concrete platform or steel pad and then fasten it with appropriate screws and bolts.
Ensure the duplex filter is firmly fixed to avoid unnecessary vibrations.
You can remove the plugs on the inlet and outlet ports. Now connect the pipework and it should be free from any form of tension.
Whenever you are planning to connect the pipework to the duplex filter, there are three options:
At the moment, you will find that quite a number of oil filtration systems use flange connections.
All these will depend on the design of the duplex filter assembly. However, I don’t recommend the welding process since it becomes cumbersome whenever you want to replace part or the entire system.
After the installation process, you can go ahead to commission the duplex filter. That is, conduct the necessary testing procedures to ensure the duplex filter assembly is ready for the task at hand.
More details about duplex filters testing procedures are in Chapter 8.
However, you should note that there are many duplex filter designs. Therefore, at times, you may make some adjustments.
Let’s look at these important adjustments:
5.2.3 Possible Adjustment When Installing Duplex Filter Assembly
Below are a few adjustments you can make to improve performance and safety of industrial filters.
First, in case the duplex filter does not have a clogging indicator, you must include a differential pressure gauge. You will install this gauge between the inlet and outlet ports of the duplex filter.
This way, you can know when the duplex filter is clogged and requires replacement. For instance, whenever there is a pressure loss of 5 psi, it is advisable to change the duplex filter element.
Second, you need a vent valve on top of every duplex filter assembly. In most cases, the modern duplex filters have a vent plug that helps to purge air.
It will always ensure an equilibrium air pressure within the duplex filter housing.
In summary, installing the duplex filter involves:
- Verifying the specifications of the duplex filters
- Preparing where you want to install the machine
- Fastening the machine on the installation platform
- Fixing the piping systems and testing the duplex filter
Clearly, it is a simple and straightforward, though very systematic.
In the next chapter, you are going to learn about another critical aspect of the duplex filter. It will explore the technical drawing and design of duplex filter systems.
Duplex Filter Design and Drawing
The design and construction of duplex filters must take place within the framework of strict quality control and management systems. It is only through this that you can get reliable oil purification systems.
Currently, a number of duplex filter manufacturers use Computer Aided Design (CAD) software to produce duplex filter designs. As a result, they have been able to produce complex designs and shapes of oil purification systems for a wide range of industries.
As a matter of fact, the duplex filter design and drawing will depend on a range of factors. In fact, I can neither list nor share all the possible designs and drawings available in the market.
So, for the scope of duplex filter and strainer buying guide, I will only give two examples. This will help you to understand the duplex filter design process.
Here are two examples:
Low Pressure Duplex Filter Design and Drawing
These include both the technical and final design of the duplex filter. I want you to study this design, then compare it with the second set of diagrams I am going to share shortly:
Now, let’s review the second diagram:
High Pressure Duplex Filter Design and Drawing
Below is a technical drawing of a high pressure duplex filer and the final product.
This is a technical drawing of a high pressure duplex filter
In both cases, you can see that the final duplex filter is basically a replica of the corresponding technical drawing.
So, here is the deal.
The duplex filter manufacturer must have the technical drawing first before the actual production begins.
Well, they don’t do this randomly. They have to consider many factors such as:
- Type of material
- Maximum operating pressure
- Maximum operating temperature
- Filter element
- Filter rating
I had discussed all these in Chapter 3, alongside other critical technical specifications.
As a general rule, the duplex filter manufacturers are at liberty to choose a design they feel will meet certain unique specifications. Again, whatever the standard, it conforms to certain standards and regulations.
You will learn more about quality standards and regulations in Chapter 8. This section covers all fundamental aspects about testing duplex filters.
With all these in mind, let’s now focus on the advantages of duplex filters in hydraulic systems.
Duplex Filter Advantage
Duplex filters are some of the most popular and trusted oil filtration systems available in the market. This is due to their effectiveness and reliability in this industry.
In this chapter, you are going to learn about duplex filter advantages. Below are 7 main advantages of duplex filters:
1. It’s Easy to Replace Filter Element
Changing filter elements in duplex filters is a simple process that does not require sophisticated tools and accessories. In fact, you can do this in less than 30 minutes.
Simply unlock all the bolts, use the handle to lift the lid, then remove and replace the filter element.
As you can see, you will simply:
- Unlock all nuts and bolts
- Lift the lid with the handle
- Open the lid to access the filter element
This is the simplest procedure whenever you want to maintain any oil purification system.
Later in Chapter 10, you will learn how to change the cartridge of a duplex filter.
2. High Dirt Holding Capacity
A critical aspect in oil filtration systems is the dirt holding capacity. It basically refers to the amount of contaminants a filter element can hold before exceeding the allowable back pressure.
Normally, the design of the filter element and duplex filter housing guarantees a high dirt holding capacity of these oil filtering machines.
Some of the key aspects that affect the dirt holding capacity of duplex filters include:
- Pore size; these are the openings within the filter medium. If you analyze the anatomy of filter elements, there are small pores.
- Pore density; this basically refers to the number of pores within a specific area
- Filter medium; it refers to the type of filter material. It can be aluminum, stainless steel, cellulose or any other synthetic material./li>
In short, irrespective of the duplex filter design, you are always sure of a high dirt holding capacity.
3. No System Down-time During Maintenance
Shutting down a hydraulic system can be costly. This is why a duplex filter provides another pathway during maintenance.
As you can see from this duplex filter, the two housings are identical. So, whenever there is maintenance, you will simply redirect fluid to the second strainer.
Therefore, as you service the first duplex filter, you will simply redirect fluid to the second strainer. It is an efficient way to ensure seamless and uninterrupted flow at all times.
4. Simple and Easy to Operate
After installing a duplex filter as highlighted in Chapter 5, other operations are simple and easy. In fact, you don’t have to hire a trained person to go about these procedures.
From the clogging indicator, you will know when to change the filter element. Once you get the signal, simply use the lever handle to chance the direction of flow.
This is an easy and simple process.
5. Reusable Filter Element Hence, a Reducing Cost of Operation
Quite a number of duplex filter designs feature removable filter elements. You can open the duplex filter basket, clean the filter element and replace it back.
You can only replace the filter element when it gets damaged. However, this can take some time.
Ideally, replaceable filter element significantly reduces the cost of operating a duplex filter.
6. Provides a Large Filtration Area
Duplex filter design provides a large filtration area. Remember, a large filter area ensures a low flow resistance within the filter element.
As a result, this will increase the dirt holding capacity of the filter, which in turn increases its service lifespan and performance. By the end of it all, such oil purification systems tend to have high filtration efficiency.
7. A Range of Filter Elements Available
Depending on the design and shape of duplex strainer basket, the filter elements come in a wide range of shapes and designs. This makes duplex strainers a perfect choice for most applications in hydraulic systems.
Even though duplex filter and strainer may have many advantages, there are certain disadvantages that you have to deal with. These include:
- Heavy weight due to the construction design
- Size tends to be large
- High initial cost, especially for custom designs
All in all, duplex strainer and filter offer a perfect oil filtration solution in most hydraulic systems.
To enjoy all these advantages, you need to choose high quality duplex filters. This is why you should know how to test oil filtration equipment.
You will learn about all these in the next chapter.
How to Test a Duplex Filter
Quality testing is an important procedure in oil filtering machines. It is through this that you can predict performance and integrity of the oil purification systems.
I know there are many standards that guide the filter and filter media test procedures. This may also vary from one region to another.
However, for the scope of this duplex filter and strainer, I will focus on the universal standards.
Normally, a duplex filter testing procedure is a critical process where the manufacturers investigate many aspects such as:
- Integrity of the duplex filter
- Thermal and chemical compatibilities
- Filtration efficiency
- Retention capability
- Bacterial retention
- Absolute rating
- Pressure loss
- Flow rate
- Rated pressure
- Collapse pressure, etc.
That is, the testing procedures aim to examine every aspect that may affect the oil filtering machine. To achieve these, the duplex filter manufacturers may work with other organizations or institutions such as the Institut de la Filtration et des Techniques Séparatives (IFTS).
Now, let’s review some of the most important procedures in testing duplex filters:
8.1 Quality Tests for Duplex Filter Housing
Chapter 4, section 4.1 covers all the intricate details of duplex filter housing. From that section, it is quite clear that this is an assembly of different components.
During and after the manufacturing tests, the duplex filter manufacturers mainly focus on the following key quality tests:
8.1.1 Leakage Tests
The duplex filter has many joints with different connections that are threaded, flange or welded. All these joints must remain leak proof at all times.
Therefore, the duplex filter manufacturer must use an appropriate testing equipment to ensure there is “zero” leakage.
Here are a few tests that can eliminate leakages:
- Test the seals to ensure there is no leakage irrespective of the operating pressure and temperature. Quite a number of oil filtration equipment use O-rings that meet the ASTM D1414 standards.
- Valve must pass all quality tests; they must pass leak proof and pressure tests. Among the key aspects you need to determine include operational, opening and closing pressure. All these must be in conformity with the valve standards.
- Use appropriate connections to prevent unnecessary leakage
In addition to these, adopting appropriate duplex filter assembly techniques will also prevent unnecessary leakages.
Clearly, you need to test every part for possible leakages to guarantee that the duplex filter remains leak proof.
8.1.2 Pressure Tight Test
As evident in Chapters 3 and 4, pressure is an important aspect you must test in a duplex filter design. It is quite clear that the magnitude of pressure determines the construction and choice of material.
In most cases, duplex filter and strainer manufacturers tend to analyze pressure alongside flow rate. This basically results in a number of line graphs which give a clear picture of pressure drop and flow rate.
Conducting pressure tight tests is critical in the sense that, any unnecessary fluctuations may affect the overall performance of a duplex filter. For example, inaccuracies in pressure fluctuation will affect the clogging indicator and filter element.
The point is, testing the overall structure and design of a duplex filter will guarantee consistent pressure in the entire system. Besides, you will also have a leak proof filtration machine.
Throughout this section, the main focus was on how the hydraulic fluid can enter and exit the duplex filter system. That is, without any leakages or unnecessary pressure drop.
But remember, the reason why we have a duplex strainer is to remove contaminants.
This now brings us to a very critical question:
How can we attain an optimal filtration from these systems not the fluid can flow without leakages or unnecessary pressure drop?
Here is exactly what you need to know:
8.2 Filter Element Quality Tests
The duplex filter element must pass certain fundamental tests to remove all contaminants in the hydraulic system.
In this section, you are going to learn about some important aspects of duplex filter element quality tests.
Normally, the quality tests aim to ensure the filter elements meet the set ISO fluid cleanliness levels. To achieve this, the duplex filter manufacturers subject all filters to certain tests to ensure they remove contaminants efficiently.
Let’s look at some of the most critical tests that will ensure efficiency in duplex filters:
8.2.1 Duplex Filter Element Capture Efficiency
The ISO 16889 defines a suitable standard for determining the capture efficiency of duplex filters. Quite a number of manufacturers use the multi-pass tests to determine the capture efficiency of a duplex filter element.
Below is a diagram of a multi-pass test for duplex filters:
This hydraulic filter test is done in controlled conditions according to the ISO 16889 standards.
As you can see from the multi-pass test circuit above, you will put the test filter in hydraulic circuit. You will then pass a contaminated fluid through the hydraulic circuit, followed by a fluid with a known amount of contaminants (ISO Medium Test Dust).
Samples are then taken both down and upstream of the test filter. So, at this point, the amount of ISO MTD added to the system before the bypass is the dirt holding capacity of the filter.
According to ISO16889, we define the capture efficiency in terms of a ratio, which is denoted in terms of beta (β). Below is an image illustration filter ratio in terms of β.
This is an illustration of filter efficiency. Image source: Machinery Lubrications
In short, the multi-pass testing procedure focuses on the following integral issues:
- Contaminant holding capacity of duplex filters
- Duplex filter element differential pressure
- Efficiency in removing dirt particles
Depending on the specific applications of duplex filters, you may adopt the following ISO standards:
- 4548 – 12 in lube oil filters
- 19438 for fuel filters
- 16889 mainly for hydraulic filters
By adopting these standards, it is quite easy to improve effectiveness and efficiency of duplex filters.
Another critical aspect whenever you are testing duplex filters is the retention efficiency.
8.2.2 Duplex Filter Element Retention Efficiency
It defines how effective a duplex filter can retain particles. Here, the main focus is on comparing the filtration ratio during three different scenarios:
- Constant flow rate
- Increasing flow rate
- Decreasing flow rate
Apart from these, other essential quality assessment procedures are:
Quality assessment for duplex filter element
Basically, you need to buy an oil filtration system whose filter elements meet high quality standards. By doing so, you will save the entire hydraulic system from possible damage by contaminants.
Even with a high quality filter element, there are certain factors that will still reduce their service lifespan significantly. This can increase the cost of operating a hydraulic system.
It is for this reason that you need to know the factors that affect the service lifespan of a duplex filters and how to fix them.
You will learn about all these in the next chapter of this duplex filter and strainer buying guide.
Factors That Affect Duplex Filters Service Life
It is a basic knowledge that failure in any of the components can be catastrophic. It will not only affect the duplex filter, but also the entire hydraulic system.
In this section, you will learn the about critical factors that affect the service life span of duplex filters. These factors include:
9.1 Design of the Filter Element
In any hydraulic filtration, you must evaluate the design of a filter element. This is because it will affect the performance and reliability of a duplex strainer.
When it comes to duplex filter design vs. the service lifespan of a duplex strainer, you must analyze every component that contributes to the overall efficiency and performance.
This will require that you pay attention to the following key components:
- Bypass valve that protects filter element from damage.
- Filter head, which covers the filter element and may serve as a mounting pad.
- Filter element; this is the section that traps contaminants.
- Filter bowl; it contains and protects filter element. It is this section which threads into filter head.
By analyzing the design properly, you can easily optimize efficiency and reduce possible filter failure. This will only be possible if you consider:
- Flow rate vs. pressure drop; for example, in most cases, the filter element design is such that the initial pressure drops within the housing and element is less than 50% of the bypass valve setting.
- Dirt holding capacity of the filter element; the dirt holding capacity will obviously affect the element life and so is that of the duplex strainer.
- Filtration efficiency; go for filter elements with higher efficiency since this guarantee less downtime and maintenance costs.
- Ability of the filter elements to maintain efficiency. This is also the beta stability, which determines how a filter system performs over time.
Remember, high pressure drops within the duplex filter can be catastrophic to the entire hydraulic system.
Take for instance, in cold weather conditions the hydraulic oil may have a high viscosity causing a high pressure drop within the filter element. As a result, this will cause a bypass valve of the duplex filter to open.
Depending on the duplex filter design, the unfiltered oil may pass into the system that can eventually cause damage.
It is for this reason that you will find duplex filter manufacturers opting for coarse filter elements. This is common in situations where it is nearly impossible to increase the pore size of the fine filter element.
So, you should remember this at all times:
The bypass valve setting will determine the maximum pressure drop across the duplex filter assembly. Therefore, to ensure the duplex filter remains effective and serves you for a long period of time, its bypass valve cracking pressure should be higher.
In short, you must evaluate the design of the filter element to reduce unnecessary wear in hydraulic systems.
9.2 Compatibility between Hydraulic Fluid and Duplex Filter
Is the hydraulic fluid compatible with both the duplex filter housing and filter element?
Compatibility is a critical aspect that determines the service lifespan of duplex filters. Generally, the duplex strainer and filter should be compatible with the hydraulic fluid, contaminants, air, etc.
Furthermore, you should evaluate other environmental factors that may affect the compatibility of hydraulic fluid and the system. For instance, an increase in temperature will catalyze any chemical reactions that may degrade the duplex filter system.
These are different types of oil filter elements. Image source: Elixir of Knowledge
There are three factors that determine how filter elements react whenever you are evaluating hydraulic fluid system compatibility:
Temperature: As I had mentioned earlier, changes in temperature affect the rate of chemical reaction. In fact, there are rare occasions where a unit increase in temperature may double or triple the rate of chemical reactions.
Hydrolysis: It refers to instances where molecules of water transmit acidity into the hydraulic system. Besides, water may also react with some metals.
Oxidation: This is where the hydraulic oil mixes with oxygen to produce other chemicals such as acid that may reduce the lifespan of the duplex filter element. The rate of oxidation may increase depending on the nature and type of contaminants.
These imply that, failure to evaluate compatibility between the hydraulic fluid and system components may lead to system degradation.
9.3 Working Temperature of Duplex Filter
Every duplex filter assembly has a unique temperature rating. You can find this information in the duplex filter technical specifications.
Normally, the temperature rating of a duplex strainer will determine the type of material and other specifications.
In sections 9.1 and 9.2 of this chapter, it is quite evident that a change in temperature may affect the viscosity of oil and influence chemical reactions, respectively. All these processes will eventually affect the service lifespan of the duplex filters.
For instance, below is a graph showing how temperature affects the viscosity of oil:
This is a graph of viscosity vs. temperature. Image source: KEW Engineering
Apart from these, thermal expansion is also another phenomenon that may compromise the integrity of duplex filters. That is, as the duplex filter parts expand and contract, they may either deform or separate.
In a nutshell, temperature can affect the efficiency and reliability of duplex filters, hence, reducing the service lifespan.
9.4 Fluctuations in Flow Rate
From the technical specifications of duplex filters, you will realize that each oil purification system has a unique nominal flow rate. Therefore, it is important to choose a duplex filter that meets a specific flow rate.
At times, there could be fluctuations in flow rates that can be many times above the pump output. These fluctuations may cause deformation of total failure of the duplex filter element.
Duplex filter flow rates
Moreover, under certain circumstances, these fluctuations may cause weaknesses in certain components. This will in the long run reduce the lifespan of a duplex filter assembly.
9.5 Quality of Parts and Components
It is a common knowledge that oil filtration system with low quality parts will definitely not serve its purpose for a long time. This is why a professional duplex filter manufacturer will test all components and parts as per the set quality regulations.
Parts of duplex filters
Again, for the recommended quality tests for duplex filter components please revisit Chapter 8.
9.6 Misoperation of Duplex Filter
Although operating a duplex filter may seem to be a simple process, following a wrong procedure can be catastrophic. For example the following operations can quite risky:
- Over tightening the bolts and nuts
- Using wrong parts and components
- Failure to replace filter elements in time
- Turning the lever handle without opening balance valve
- Forcefully squeezing the valves
In short, do not go contrary to the duplex filter manual or product guide. You will not only damage the duplex strainer and filter, but also invalidate its warranty.
9.7 Maintenance Procedure
Failure to follow the right duplex filter maintenance procedure will reduce its service life span significantly.
Remember, adopting proper cleaning and maintenance procedures is a sure way of ensuring optimal performance of oil purification systems. You will learn more about this in Chapter 10.
From this chapter, it is quite clear that there are certain factors that you can control. However, others are design issues that the duplex filter manufacturer must adjust during the production stage.
Therefore, it is important that you order for an oil filtering machines from reputable duplex filter manufacturers. Such manufacturers adhere to strict quality control procedures.
At the end of this duplex strainer and filter buying guide, you will find top 10 duplex filter manufacturers.
Duplex Filter Maintenance Guide
You can recall the main focus of Chapter 9 was the factors that affect the service lifespan of duplex strainers and filters. One of the main factors that came out clearly is adopting proper maintenance process for duplex filters.
Now, this section, will take you through three critical processes of the duplex filter maintenance guide. These include:
- How to change the cartridge of a duplex filter
- Duplex filter cleaning guide
- Troubleshooting duplex filters
These are critical procedures that if conducted properly, will increase the service lifespan of any oil filtration equipment.
Let’s discuss these factors one at a time:
10.1 How to Change the Cartridge of a Duplex Filter
As mentioned in the previous chapters of this duplex strainer and filter buying guide, this accessory should guarantee an uninterrupted flow in hydraulic systems.
So, even as you plan to change the cartridge of a duplex filter, it must not interfere with the normal operations of the hydraulic system.
Let’s see how to go about this process:
10.1.1 Monitor Clogging Indicator and Change Direction of Flow
First, it is the clogging indicator that will show when to change the cartridge of duplex filter. This is, once the filter element gets clogged, it will send a signal.
As mentioned in Chapter 4, this signal will depend on the differential pressure across the filter system.
This is an example of a clogging indicator. Image source: Hydraulics & Pneumatics
Second, following an indication that the duplex filter element is clogged or faulty, you must transfer flow to the second filter that was on standby. Here is how you can go about this process:
- Ensure the pressure between the two vessels is equal and that the standby filter is filled with fluid. You can achieve this using the using the duplex filter balance valve or pressure equalizing line.
- You can then change the position of the changeover valve. This will divert the flow to the standby filter system (clean filter element).
- After the changeover, you can then close the pressure balance valve or pressure equalization line.
So, this will mark the end of step 1.
Next, this is what you should do:
10.1.2 Open the Duplex Filter Housing and Change the Cartridge
After diverting the flow, it is now time to open the duplex filter housing. At this point, here is what you should do:
- Begin by opening the vent valve in the duplex filter housing. This will release any pressure that could be in the duplex filter housing, thereby reducing it zero.
- Next, open the duplex filter drain system so that you can remove the remaining fluid in the duplex filter. Use a suitable container to hold this fluid since it is a sure way of keeping your working area clean.
Also, this will prevent the dirty fluid from passing into the clean side of the duplex filter assembly.
- Use appropriate tools to loosen all bolts or nuts to remove the duplex filter cover. You can use the handle to lift the cover carefully, plus all the sealing assembly.
- At this point, you can now access the duplex filter cartridge and carefully remove it from the housing.
- Change the duplex filter cartridge. It should have the same specification as the old one or meet the desired filtration criteria.
These are different types of filter cartridges. Credit: Seal Meh
- Carefully insert it into the duplex filter housing, replace the sealing assembly (O-rings) and the cover.
- Fix the cover in place by tightening the bolts
By following these 7 simple procedures, you shall have changed the cartridge of a duplex filter. So, you can move to the last step.
10.1.3 Put the Duplex Filter in Standby Condition
This is the last stage after changing the cartridge of a duplex filter. Again, this is a simple process that involves the following:
- Open the pressure balance valve for a short time, leaving the vent valve open
- As soon as the fluid begins to flow through the vent valve, you should close the valve
- Go ahead to examine the duplex filter housing for any leakage
- In case there is no leakage, you can close the pressure balance valve
By doing all these, your new duplex filter housing (with the new cartridge) will be ready for use (for the next changeover).
Clearly, this is a systematic and simple process.
In case this is your first time to go about this process, you can refer to the technical drawings of duplex filters in the product manual/catalogue. Duplex filter manufacturers do label every component of these filtration systems.
With all these in mind, now let’s move to yet another critical aspect of the duplex filter maintenance guide.
At times, the filter element or cartridge may not be faulty. The filter element could be in good condition and may only require cleaning.
So, how do you go about the process?
10.2 Duplex Filter Cleaning Guide
Cleaning is an important aspect of the duplex filter changeover procedure.
In section 10.1 of this chapter, the main focus was on how to change the duplex filter cartridge. Well, the process of accessing the duplex filter element still remains the same as that of the cartridge.
This chapter will focus on how to clean the duplex filter housing and filtration element.
10.2.1 Cleaning Duplex Filter Element
As I had mentioned earlier, you can do the cleaning process as you change the duplex filter cartridge. So, the process of opening and closing the duplex filter housing still remains the same.
In most cases, immediately you open the drain plug, even before taking out the blocked filter element, flush the contaminants or dirty particles on the bulk board. You can then close the drain plug and remove the used filter element.
Details of duplex filter system
Normally, the procedure here will depend on the type and construction of the filter element. For example:
For paper or glass fiber filter elements, you have no option but to replace them with new ones once they become clogged.
On the other hand, for duplex filter elements made of metal mesh, choose an appropriate solution to clean those that are dirty or clogged. This implies that you can reuse these filter elements many times.
10.2.2 Cleaning Outer Casing of Duplex Filters
Well, the duplex filter casings are made from different materials such as iron, bronze, stainless steel, etc. Again here, you will choose an appropriate solution and material to wipe the entire surface.
Moreover, the surface finish or treatment will determine the type of cleaning detergent and procedure.
As you can see, this is a simple process too.
It is also important to note that there has been many technological innovations in the duplex filter industry and so is the cleaning process.
For example, we have self-cleaning duplex filters.
Such oil purification systems reduce the manual cleaning of duplex filters. This increases efficiency by reducing possible downtime in the hydraulic systems.
Even though they come in many designs, the most common options involve scrapping of contaminants of dirt that move to a sludge chamber. The duplex filter is then set to drain all contaminants in the sludge chamber at certain intervals.
Another technology is the backwash duplex filters. Here, there is no need to open the duplex filter casing.
As the name suggests, all you need is to close the duplex filter, then backwash it to remove all contaminants.
Of course, there is a lot of research still going on about how to effectively clean the duplex filters.
Apart from changing cartridge and filter element, another essential process is troubleshooting duplex filters. This is a critical process in duplex filter maintenance guide.
10.3 Trouble Shooting “leakage” Problem of Your Duplex Filter
The effects of leaking hydraulic systems can be devastating to both the machine and the surrounding environment. Some of the most common effects of such systems include:
- Cost of operating the machine will be higher due to wastages
- Certain hydraulic fluids contain dangerous chemicals that pollute the environment
- High chances of accidents, especially for flammable hydraulic fluid
- Premature failure of the machine, etc.
Therefore, to avoid all these, every machine in the hydraulic circuit must guarantee “zero leakage” at all times. This way, you can easily maximize on your profit margin.
At times, you may experience leakages in duplex filters and hence the need for troubleshooting this problem in time.
Below are 6 of the most common causes of leakages in duplex filters and possible solutions:
10.3.1 Damaged, Deteriorating or Aging Sealing Parts
To make a duplex filter airtight and to prevent leakages, these systems have various types of sealing mechanisms. The shape of a sealing mechanism will depend on the duplex filter design.
In most cases, whenever there is a leakage in oil purification equipment, it is important that you inspect all joints. This could be due to aging or deteriorating sealing mechanism.
Therefore, the best option is to replace it.
10.3.2 Incorrect Operation of the Duplex Filter
Can you remember the list of factors that affect the service lifespan of duplex filters that were discussed in Chapter 9?
Operating a duplex strainer and filter without following the recommend instructions is one of them.
By doing so, you may break vital components of the duplex filter such as transfer valves or drain valves. All these can result in leakages.
To avoid such unfortunate scenarios, you must follow all instructions in the product manual.
10.3.3 Poor Joints
Nearly 89% of all leakages occur at the joints. For instance, a duplex filter may feature threaded, flanged or welded joints.
Any failure in these joints may result in significant leakages. Take for instance, when the welding technology results in an empty or leaking joint due to soldering.
Another example is the flange connection:
This is an example of flange connection. Source: Nord Fab
Definitely, when you combine metals whose degree of linear expansion vary broadly, there is a high chance of leakages at the joint.
In short, you should inspect the joints regularly and ensure they are intact.
10.3.4 Improper Assembly
Quite a number of duplex strainers and filters come from the factory when they are already assembled. However, the problem comes when you are:
- Replacing filter element or cartridge
- Connecting the pipe systems
During these two scenarios, you may end up squeezing, seals hence causing damage to the components in the process. In such situations, your duplex filter assembly will definitely begin to leak.
To avoid this, you must follow the recommended installation procedures and use appropriate tools. More importantly, you must be careful and keen.
10.3.5 Incomplete Structure of the Duplex Filter Element
Filter elements and cartridges come in a range of shapes and designs, especially during this time when duplex filter manufacturers focus on producing their patented and custom options.
You must review the structure of the filter element as per the manufacturer’s design and compare it with that in your duplex filter.
In some instances, this leakage could be due to some faulty sections of the filter element. Remember, this will also result in improper filtration where the hydraulic system may get contaminated.
So, you should ensure the duplex filter element has been tested the structure integrity before installation.
10.3.6 Failure of the Bypass
Inappropriate selection and setting of the bypass valve may result in leakages in the duplex filters. At times, this may result in abnormal opening and closing of the bypass valve that make the entire hydraulic system unstable.
Under such circumstances, you need to inspect the bypass valve and make the necessary adjustments. Remember, it is the bypass valve that ensures oil reaches other components in the hydraulic system whenever the filter element is blocked.
By assessing all these 6 factors and making appropriate adjustments, your duplex filter assembly can operate without any leakage. Remember, this is always the goal of all duplex filter manufacturers and technical staff in the factories.
As a matter of fact, it requires strict and consistent quality inspection at every stage of the oil filtering machine manufacturing process.
So far, Filson Filters is among the few companies in the industry that guarantee zero-leakage in their duplex filters.
Now that you know every critical aspect of duplex strainers and filters, let’s review the various applications of this oil purification equipment.
Duplex Filters and Strainers Applications
Duplex filters and strainers are suitable for hydraulic systems that require an uninterrupted flow.
As you can see from the previous chapters, the design is such that, at any given point, there is a standby filter. Therefore, if one duplex filter is clogged, you can switch to the second.
Meanwhile, you can go about all the other routine maintenance for cleaning or changing the dirty filter element. All the duplex filter maintenance processes are explained in Chapter 10.
A simple illustration of duplex filter removing contaminants in various practical applications
For a fact, you can use duplex filters and strainers in many applications. Some of the most common examples include:
11.1 Construction Machinery
Duplex strainers are available in a range of shapes and designs to suit various construction machineries.
It does not matter whether you are using an excavator, dozer, loader, grade, scraper or any other system that depend on hydraulic fluid. What matters is the ability of the system to provide continuous flow of hydraulic fluid.
With an appropriate duplex filter, your construction machines will be free from:
- Contaminated oil
- Frequent oil replacement
- Parts and component replacement
- Frequent downtime, etc.
As a result, they will help to extend the service lifespan of the construction machinery.
11.2 Mining Industry
Whether in the gold, oil or precious stone mining industry, you may require uninterrupted flow of fluid to and from the mining site.
For instance, in the mining industry, you will need a continuous flow of water to cool tools and equipment. This is where a duplex strainer and filter becomes handy.
11.3 Petrochemical & Chemical Industry
Consistent and uninterrupted flow is critical in either petrochemical or chemical industries. It is for this reason that nearly all petrochemical & chemical industries opt for duplex filters and not simplex filters.
Depending on the operating pressure and flow rate of the system, there is a range of duplex filter and strainer that meet the specific needs in this industry.
11.4 Lube Oil Systems
There are heavy duty duplex filters for oil filtration systems. They come in different flow rates and pressure ratings.
Depending on the type of lube oil system, these duplex filters and strainers are made from cast iron or stainless steel. You can use these filters in fuel oil filtration, diesel, compressor and turbine and lube filtration systems.
11.5 Paper Coating
Duplex strainers and filters are suitable for paper coating and paint industries. They eliminate all possible contaminants that may affect the outcome of the final product.
In the recent past, a number of paper coating duplex filters feature sieve type filters with vibratory mechanisms. The vibrations increase the overall efficiency of such duplex filters.
11.6 Waste water
In these systems, the duplex strainer and filters remove all waste in water depending on the size of perforations on the element. By removing these wastes to meet specific safety standards, you can use this water for other applications.
Since you may not have control over the source of waste water, especially if it is a municipal system, it is only a duplex filter that can guarantee smooth and seamless operation.
11.7 Power Plant
In power plants, we have generators that require clean fuel flowing continuously to generate power. At the same time, we need clean oil to cool transformers.
To guarantee this, you need fuel and oil duplex strainers and filters. This way, you will be sure of a system that generates power continuously without experiencing any problems due to contamination.
11.8 Offshore Oil Industry
Whether in water wells or drilling rigs, a duplex strainer and filter plays an integral role in ensuring efficiency and reliability of the entire process.
This is because with an appropriate duplex filter, you can control flow and maintain cleanliness of the system throughout. Besides, it will reduce possible contaminations that may result in costly oil extraction.
Duplex filter is a perfect marine filtration solution. The design of these filters can handle a wide range of fuel oil needs. They can filter fuel or lubricating oil depending on their designs.
Mostly, marine duplex filters are easy to maintain and they come in modular designs. They feature compact filters and leak-free operation.
11.10 Contamination Monitoring Systems
In either on-line or off-line contamination control, duplex strainers and filters are the best accessories you can trust for this task.
Irrespective of the type of industry or solution, the duplex filters come in many designs and shapes with different technical specifications. Therefore, you can adapt it in either contamination control or analysis.
In short, you can use duplex strainers in nearly all hydraulic filtration systems.
With all these in mind, it is now important to know some of the key factors to consider before you buy duplex strainers and filters.
How to Choose a Perfect Duplex Filter for Your Industry
As you will realize in the Chapter 3, there are many duplex strainer and filter manufacturers in the global market. Not all these companies follow the strict quality tests as highlighted in Chapter 8.
It is for this reason that you need to know the basic factors to consider before buying a duplex filter. Basically, this section is a recap of the most critical factors mentioned in this duplex filter and strainer buying guide.
Here is how to choose a perfect duplex filter by considering these most important factors:
12.1 Particle Characteristics of Hydraulic Fluid
Here, the type of hydraulic fluid you intend to filter will determine the nature and design of filtration medium. The fluid can be in the form of oil, water or gas.
By knowing the physical and chemical characteristics of the fluid particles, it will be easier to choose the right material and design of a duplex filter. Of course, this will also go hand in hand with the type of application.
In other words, you must understand the hydraulic fluid contamination first.
Different types of hydraulic fluid
With this information, you will choose a filter element with the right micron size and type of material that suits that specific application. Besides, you will choose a material that does not react in anyway with the hydraulic fluid, irrespective of the temperature or pressure changes.
In short, this is the first aspect that will determine type of duplex filter you can choose for your industry.
12.2 Max. Flow Rate and Viscosity
You need to know the minimum, nominal and maximum flow rate in any hydraulic system. All you need is to establish the flow rate of your system, then use technical specifications of duplex filter to choose an appropriate accessory.
But, why should we consider the viscosity of hydraulic fluid?
Basically, viscosity of hydraulic fluid is inversely proportional to the rate of flow. Of course, this is quite clear when you analyze the Poiseuille’s Law.
You can summarize this as:
Viscosity vs. flow rate
What I am trying to say is that:
Whenever you are choosing a system depending on the flow rate, it is important to consider the fluid viscosity too.
A 2 inch filter element can handle fluid flowing at 100gpm but this may not work for a 150gpm system. For the 150gpm, you need a larger filter.
The concept is that simple.
Also, for other duplex filter designs with the backwash mechanism, specifying the maximum flow rate alone is not enough. Instead, you must specify the minimum flow rate too.
12.3 Working Pressure
Another critical parameter here is the working pressure of duplex filters. Working pressure is an important aspect of classifying duplex filters.
It is for this reason that in Chapter 3, we did classify various types of filters as low, medium and high pressure duplex filters.
Fundamental aspects about duplex filter working pressure
Here are the key aspects about duplex filter working pressure you must know:
Maximum Working Pressure
This is the pressure above which the hydraulic fluid may damage the filter element. So, whenever you’re buying a duplex filter, the maximum pressure in your hydraulic system must not go beyond the maximum pressure.
Of course, this will be based on a critical analysis of pressure in hydraulic systems.
Minimum Working Pressure
Whenever you intend to use self-cleaning duplex filters, it is critical to specify the minimum working pressure of the system. This is because once you engage the duplex filter flushing mechanism the system must maintain the minimum operating pressure.
Apart from these two, another critical aspect about the pressure you must examine is the pressure drop.
Why is pressure drop important?
Pressure drop in duplex filters refers to the pressure loss within the piping, valve and filter elements. Among the key factors that contribute to pressure drop include:
- Type of filter media
- Flow rate
Normally, it is from this pressure drop that you will know when to change the duplex filter.
Remember, in Chapter 9, we did focus on factors that affect the service lifespan of duplex filters. There is a lot of important information about pressured drop in relation to the performance of duplex filters.
In short, you need to take note of the maximum allowable pressure drop too alongside other parameters.
12.4 Working Temperature
Duplex filters have a temperature range within which they guarantee optimal performance. For instance, very low temperature may cause hydraulic fluid to freeze within the filter elements.
On the other hand, very high temperature may damage the filter element. Also, it may cause other chemical reactions that may affect different components of the duplex filter.
So, before you buy a duplex strainer and filter, it is important to specify the working temperature. This way, you can optimize all operations of the duplex filter.
12.5 Installation Dimensions
At any time before you begin the process of installing duplex filters, it is important to consider the available space and weight. With this information, you will prepare the space where you intend to install the duplex filter.
This information about the length, width, height and weight is available in the duplex filter technical manual.
12.6 Pollution and Environmental Risk
Pollution and environmental risk are critical aspects to consider whenever you intend to filter toxic liquids. Under such circumstances, you should go for custom made or specially designed duplex filters that can prevent possible pollution or environmental risks.
Such duplex filters are common in chemical and petroleum processing industries.
In such situations, the duplex filter manufacturer may use special material, valves or connection.
12.7 Filtration Accuracy
Normally, the filtration accuracy will depend on the overall design of the duplex filter assembly. This will range from the inlet/outlet ports, filter element and valves, among other special features of the duplex filter.
The filtration accuracy may vary from 1 to over 500μm, depending on the specific applications and design of the cartridge filter element.
12.8 Connection Type
How will you connect the duplex filter assembly to the existing hydraulic system network?
In most cases, you can opt for flanged or threaded connections.
You may also go for welded connections. The disadvantage with this connection is that, replacing the entire duplex filter assembly is cumbersome.
12.9 Cost of Operation
You should consider the costs associated with operating a duplex filter. In most cases, you can have manual or self-cleaning duplex filters.
Self-cleaning duplex filters are common in hazardous or remote areas. Such duplex filter assemblies have sophisticated designs and are slightly expensive.
In addition to this, you should factor in the cost of cleaning duplex filters alongside waste disposal.
Apart from these, other factors may include design, manufacturer and color of the duplex filter.
By considering all the 9 factors, there is a high possibility that you will get a duplex filter assembly that meets your unique specific applications.
Now, where can you buy high quality duplex filter assembly?
Below are top duplex strainers and filters manufacturers in the global market.
Top 10 Duplex Filters and Strainers Manufacturer in Global Market
Are you planning to buy duplex strainers and filters for your oil purification system?
This chapter covers top 10 industrial filters and basket strainer manufacturers in the global market. All these filters are subjected to strict quality tests.
These duplex filters and strainers manufacturers include:
Eaton is a leading duplex filter manufacturer, established in the United States. It is popularly known as a power management company that provides solutions in many industrial processes.
Eaton’s official website
The company manufactures duplex filters of different designs and shapes for a range of hydraulic systems. They also come in different models with custom designs available upon request.
As a result, the duplex filter systems can have basket strainers that range from 5 to 24 inches. This will depend on the specific applications of duplex filters.
The duplex filters are made from different materials such as stainless steel, bronze, iron or carbon steel. While the connections are either flanged or threaded.
Hydac is a German company that produces a range of accessories for hydraulic machines and equipment. With many decades in this industry, Hydac produce many hydraulic and lubrication filters that are available in different shapes and designs.
Hydac official website
As a professional duplex basket strainer manufacturer, Hydac produces fully assembled equipment as well as other accessories. These include filter elements, clogging indicators and other spare parts.
Being an industry leader in duplex filter design and assembly, Hydac adheres to strict manufacturing and quality inspection standards.
Currently, Hydac has many subsidiary companies across the globe to serve its ever growing market demands.
Mahle is a German company with numerous subsidiary companies and partners with major companies across the world.
Mahle official website
The company invests in research and development to provide innovative solutions in hydraulic system industries. So far, Mahle is known for its patented single-hand duplex filters that guarantee zero leakage on switching.
Their duplex filters range from low to high pressure duplex filters that come in a range of sizes and designs.
Most Mahle duplex filters feature modular and compact designs. Being an industry leader in duplex filter manufacturing, Mahle duplex filters are designed to meet the standard quality threshold.
13.4 Pall Corporation
This is an American company that has diversified in many industries where it provides both standard and custom duplex filters.
Pall Corporation duplex filters are known for special designs such as those with Athalon™ element construction. Some have an anti-static design.
Furthermore, they have patented Ultipleat®, among other features that enhance performance and reliability of the duplex filter.
The filters come in many pressure, temperature and flow ratings, depending on the specific requirements of the duplex filter applications.
13.5 Bosch Rexroth
Bosch Rexroth is a German company, which is one of the leading industrial filters and basket filters manufacturer. It is among the first companies to manufacturer filter elements using micro glass with a six layer design.
Bosch Rexroth feature unique design increases life cycle of filter element and dirt holding capacity by about 50%.
Currently, Bosch Rexroth is working on their new filter technology – the cyclone effect. This aims to reduce the filter change intervals by optimizing dirt absorption.
The design of the duplex filter housing comes in both standard and custom designs to meet specific application requirements in the hydraulics industry.
13.6 BOLL & KIRCH
Boll & Kirch is a German company that has specialized in filtration techniques. Broadly, it produces engine oil filters for fuel oil, gaseous and lube oil.
Others include industrial and water filtration accessories.
Boll & Kirch Company
Unlike the other 5 duplex basket strainer manufacturers, Boll & Kirch has not diversified into other industries, but instead, it focuses on filtration systems in the hydraulic systems.
This explains the reason Boll & Kirch has invested in innovative technologies such as CrNiMo steel and FouleX for its filter elements.
Another company that focuses on filtration systems is:
13.7 Filson Filters
Filson Filters is a Chinese company that designs and manufactures many duplex filters. They range from high pressure to low pressure duplex filters.
Moreover, other options such as fabricated duplex strainers and duplex filter housing are also available. They all come in different designs, materials and shapes, depending on the specific applications of duplex filters.
Apart from these, Filson Filters manufactures other essential filtration accessories such as simplex filters and filter carts. Of course, this is alongside other accessories such as duplex filter elements and other accessories such as clogging indicators, vent plugs, etc.
Focusing on filtration systems put Filson Filters in the same category as the Boll & Kirch.
13.8 Oxford Filtration
Oxford Filtration is yet another company that focuses mainly on all sorts of oil filtration machines among other related products. It is a U.K. based company.
Oxford Filtration duplex filter designs meet the international standards. Just like Boll & Kirch and Filson Filters, the main focus of Oxford Filtration is on various hydraulic fluid purification accessories.
13.9 HY-PRO Filtration
HY-PRO Filtration is an industrial filters and basket filter manufacturer in the United States. The company designs standard and custom duplex filters alongside other accessories for hydraulic systems.
Like other duplex strainer manufacturers, HY-PRO Filtration has improved duplex filter elements. They feature enhanced designs and material such as stainless fiber media, non-spark, etc.
13.10 Sure Flow Equipment
Sure Flow Equipment is a Canadian company that designs and manufactures duplex strainer and filters alongside other hydraulic system accessories. The company manufactures duplex filter from a range of materials for different hydraulic systems.
Sure Flow Equipment Inc.
Sure Flow Equipment invests a lot in fabricated and custom duplex strainers, alongside different filter elements.
For a fact, these are many duplex basket strainer manufacturers in the world, thou, not all companies follow strict quality standards. In fact, it can result in substandard and low quality filtration systems that can cause total failure of the hydraulic system.
Over the recent past, the Chinese duplex filter manufacturers have become a better option when it comes to the OEM partnership. Of course, this is due to their competitive prices.
Still, you have to do a comprehensive research to ensure the company follows strict quality standards.
Attaining the highest degree of cleanliness as per the ISO standards in hydraulic systems is important. But, ensuring an uninterrupted flow in hydraulic circuits is even more important.
As you have seen in this duplex strainer and filtration eBook, you need a high quality, robust and modern filtration equipment to achieve this.
It is the reason why this eBook covers critical aspects such as components, classification, working principle and maintenance procedures of duplex filters, among other aspects.
At the end of this duplex strainer and filter eBook you should be able to identify, evaluate and choose oil purification equipment that meets specific needs of your filtration applications.
- Hydraulic Filter Information – Source: Global Spec
- What is a Duplex Strainer – Source: FilSon Filters
- Hydraulic Filtration – Source: D.J. Dunn
- ISO Contamination Filtration Standards – Source: Machinery Lubrication
- Monitoring Hydraulic Filter Condition – Source: Hydraulics & Pneumatics
- Quality Tests for Duplex Filters & Filter Carts – Source: FilSon Filters
- How Oil Filters Work – Source: Mobil
- A Complete Handbook of Hydraulic Valve Technology – Source: Saroit
- Hydraulic Fitting and Flanges – Source: Target Hydraulics
- Hydraulic Filters – Source: Fluid Power World