The key features of duplex strainers will depend on their unique designs and specific applications in the hydraulic systems.

For instance, high pressure duplex filters have a unique design that can withstand up to 32Mpa.

A high pressure duplex filter drawing

A high pressure duplex filter

On the other hand, a low pressure duplex filter design is such that it can support a maximum of 1.6Mpa.

A technical drawing of a low pressure duplex filter

A technical drawing of a low pressure duplex filter

From these two, it is quite evident that the features of duplex strainers depend on a range of factors.

This article focuses on fundamental features that are common to most duplex oil strainers.

Here are the key features of duplex strainers that guarantee efficiency in hydraulic systems:

1. 2 Baskets for Smooth Changeover Ensuring Continuous Operation

Basically, this is the whole point of having duplex basket strainers.

In fact, this is actually the reason why these accessories are at times called duplex continuous flow basket strainers.

They are a perfect choice for applications where shutting down or stopping operation during maintenance can be costly.

So, what do I mean by smooth changeover in continuous operation?

Looking at this accessory, you will see that there are two equal baskets strainers.

They have the same capacity and type of strainer.

You can see this as shown below:

baskets have the same capacity and filters

The two baskets have the same capacity and filters

At any given point, only one of the baskets will be working.

You will use the lever handle to choose the strainer basket.

Once the filter element clogs, you will simply switch to the next strainer basket by turning the lever handle.

Meanwhile, you will clean and replace the filter element for the next changeover.

This way, the strainer basket will guarantee continuous flow and hence, the efficiency of the entire system.

2. Quick Opening Covers

This is a critical aspect whenever you intend to change the filter elements during any maintenance process.

The design of any industrial basket strainer should be such that you can easily open the bolt connection with standard accessories/tools.

In situations where the manufacturer opts for custom made fastening mechanisms, they should provide appropriate tools.

Here is what I am talking about:

duplex basket strainer joined with many bolts

A duplex basket strainer joined with many bolts

As you can see from the above example, an industrial duplex strainer is an assembly of many parts and components.

Normally, duplex basket strainer manufacturers use a number bolts or other fastening mechanisms that are robust and strong can withstand vibrations.

However, even when choosing a duplex basket filter, the cover should be easy to assemble and disassemble whenever there is a need.

Remember, installing duplex filters can be a challenging process, especially if the covers prove problematic to open.

Easy & Safe to Clean When Clogged

The main purpose of installing a duplex basket strainer is to ensure there is no downtime during any operation of hydraulic systems.

Therefore, you need a strainer that is easy and safe to clean/maintain when clogged.

Now, let me introduce you to important features that make this actually possible:

3. Clogging Indicator

Well, it becomes virtually impossible to know whether a basket strainer is clogged or not.

This is why a good duplex oil strainer should have a clogging indicator.

exact position of a clogging indicator in d

The exact position of a clogging indicator in duplex strainers

Basically, it is the clogging indicators that monitor the filter element.

Normally, the working principles of these clogging indicators are based on pressure difference.

In most cases, a duplex basket strainer manufacturer may opt for electronic or optical clogging indicators.

There is also a combination of the two.

Depending on the specific applications of this accessory, the manufacturer will recommend an appropriate clogging indicator.

As warning devices, clogging indicators will show the operator whenever contaminants increase in the filter element.

In short, it is the clogging indicator that will show when to replace the filter element.

4. Drain Plug

Another essential accessory is the drain plug.

Depending on the design of a duplex strainer, a drain plug is located such that it allows for easy and convenient cleaning of the filter element.

Drain plug of a medium pressure duplex filter

Drain plug of a medium pressure duplex filter

With the drain plug, you can dump oil before beginning to change the filter elements.

Normally, this helps to keep the working area clean.

With the drain plug, you can also remove some contaminants that may be in the form of sediments.

5. Hydraulic Valves

Depending on the design of industrial baskets strainer, you require certain hydraulic valves to make the changeover process smooth and reliable.

Again, the exact location of the valve will also depend on the design of the duplex basket strainer.

position of directional control valve in high pressure duplex filter

The position of directional control valve in high pressure duplex filter

Remember, the idea behind using three-way ball valves, balance valves, changeover valves or directional valves will depend on the specific application requirements.

In each case, the duplex basket strainer must have:

  • Longer service life
  • Guarantee reliable sealing
  • Allow for possible, bypassing of filter when changing the filter elements
  • Provide smooth filter element changeover

With appropriate filter elements, you will be avoiding the expensive process of shutting down hydraulic system.

In short, a duplex basket strainer with all these features will be easy and safe to maintain.

Besides, they will make it easier to increase efficiency in hydraulic systems.

6. High Dirt Holding Capacity

Good duplex basket strainer should have a high dirt holding capacity with low pressure drop.

Besides, such filters have better particle retention capability as they can handle highly viscous fluids.

At times, the duplex filter manufacturers may opt for filter cartridges with a multi-layer structure.

atomy of Oil Filter

This is an atomy of Oil Filter. Courtesy- Machinery Lubrication

Such strainers are a perfect choice for high flow rates, extremely high dirt holding capacity and increased pore structure.

They guarantee a long service lifespan, making them suitable for most industrial applications.

Unlike most filters in the market, higher dirt holding capacity industrial basket strainers feature a continuously increasing inward pore structure.

Their stable matrix guarantees high efficiency in any hydraulic system.

In short, high dirt holding capacity duplex basket strainers have a large filter area and they guarantee unmatched performance even in a broad pressure differential range.

7. Better Sealing Mechanism (Ensures Zero Leakage)

Duplex strainers must pass strict quality testing procedures to ensure they guarantee “zero leakage”.

duplex filter with a proper sealing mechanism

The above circles show various joints of a duplex filter which must have a proper sealing mechanism.

Quite a number of industrial duplex filters use high quality sealing mechanisms to ensure “zero leakage”.

The O-rings have a longer service life.

Duplex strainers that meet the “zero” leakage requirement must adhere to strict fabrication standards. This entails:

  • Choice of appropriate valves to ensure there is no leakage.
  • Adopting appropriate welding mechanisms for the joints
  • Proper assembly of the entire structure of the duplex basket strainer

Ideally, industrial basket strainers without any leakage will guarantee optimal performance in any hydraulic system.

8. Duplex Basket Strainers are Fabricated from a Range of Materials

Various types of duplex strainer filters are made from a range of materials depending on the specific application.

That is, the type of material will depend on a specific fluid you expect the system to handle.

Again, here, there are two critical aspects you need to consider:

  • Material for the duplex filter structure

When it comes to the housing, the basket strainer manufacturers can choose from aluminum, carbon, 304/316stainless steel, plastics, iron, bronze, etc.

304 316 stainless steel duplex filter housing

304/316 stainless steel duplex filter housing

  • Materials for the filter element

The element includes filter cartridge, filter modules and filter bags.

In most cases, the duplex filter manufacturer can choose from many materials such as polyethylene, polyester, cellulose, acrylic fiber, nylon, stainless steel, etc.

Different types of filter elements

Different types of filter elements

Basically, you need to choose a type of material depending on the nature of the task at hand.

In this case, you should consider the type of hydraulic fluid which can be water or special oil.

9. Different Connections Available

Depending on the specific hydraulic systems, the duplex basket strainers have many connections.

In fact, apart from the standard options, you can choose specific designs that meet custom application requirements.

A flange type of connection

A flange type of connection

Take for instance, you can choose flange, threaded or welded designs.

They all come in different sizes that meet specific requirements of a hydraulic system.

10. Vent Plug to Maintain Pressure Equilibrium

To ensure the efficiency of a hydraulic system, you should be able to control pressure in the hydraulic system.

One of the most critical aspects here is the ability to maintain pressure equilibrium.

It is for this reason why a good industrial basket strainer should have a vent plug.

exact location of vent plug on duplex filter

The arrow shows the exact location of vent plug

The vent plug provides the most efficient way of purging air, which helps to maintain pressure equilibrium.

11. Strategically Positioned Inlet and Outlet

Normally, the duplex basket strainer manufacturers indicate these ports with “IN” (or an arrow pointing inwards) and “OUT” (or an arrow pointing outwards).

The exact position of the inlet and outlet ports will depend on the design of a duplex basket strainer.

For instance, you may have the two ports on one side or on the opposite sides.

technical drawing of low pressure duplex filter

A technical drawing of low pressure duplex filter

Again, in most cases you’ll find the inlet port in the upper part and outlet on the lower section.

Still, the position of the connections is always strategically positioned to optimize flow of fluid without compromising on unnecessary pressure loss.

Besides, there should be an appropriate connection mechanism to ensure “zero leakage”.

12. Easy to Operate Lever Handle

You need this lever to transition from filter basket “A” to “B”.

A good duplex basket strainer should have a lever that is easy to use.

That is, one that you can easily switch from the two extreme ends to close and open filter basket.

With this, you will be guaranteed of a seamless operation.

Medium pressure duplex filters handle

Medium pressure duplex filters handle

As you have seen in the various duplex strainers in this article, it is quite clear that the lever handles may be positioned at different points.

At every stage, the most critical aspect is to ensure that it is easily accessible.

13. High Quality Filter Element

Again, you need to choose filter elements based on the type of hydraulic system and hydraulic fluid.

With this knowledge, you’ll choose a filter element that will increase the overall efficiency of the entire process.

Currently, duplex strainer manufacturers try to be specific when designing filter elements.

The design process is based on a series of tests to guarantee high quality and predictable performance.

Moreover, they come in different micron ratings.

The filters are environmentally friendly and easy to clean.

Different types of filter elements

Different types of filter elements

Always remember, the choice of specific duplex will depend on filtration levels, pressure drop and performance requirements.


Apart from these, it is important to choose a duplex basket strainer with an ergonomic design that guarantees efficiency of the hydraulic systems.

Again, you need to evaluate these duplex strainers based on their technical specifications.

You can find all this information in the duplex strainer catalogue.

At FilSon Filters, we have a range of duplex filters designed for many pressure levels and volume capacities.

For more information on our products, contact our technical team.

Further Reading