Are you struggling with cleaning up oil spills?

Do you find it hard to ensure safety while guaranteeing trouble free and efficient operation of machineries or systems?

Then, FilSon duplex filters & strainers offer a perfect solution.

filson filtration system

As we all know, duplex filters and strainers are widely used in hydraulic & water systems to remove contamination and prevent impurities from entering these systems.

Inappropriate sealing of duplex oil filters may cause leakage, inefficiency or abnormal operation.

Sometimes, it may result in production safety and environmental pollution problems.

Therefore, leak-free filters are the most sought after accessories by customers.

oil leak with bad duplex filter

Seals of duplex filter: Under a certain high (low) temperature, there must be no leakage in every joint of the filter at a constant maximum pressure.

So, how do FilSon duplex filters ensure “zero” leakage?

In this article, I want to explain to you 7 measures that we improve duplex strainer sealing performance.

1.Reliable And Easy-to-operate Ball-switching Structure is Offered

I am sure people who are traditionalists may still go for cone-valve duplex oil filters.

Most of them find it difficult to understand why the ball-switch duplex filters & strainers have been trending in the recent past.

duplex filters with ball valve

Of course, this is due to the desirable sealing performance of ball valve duplex basket strainer.

The reality is, traditional cone-valve dual filters are “big” “stupid” and always have serious internal leakage problems.

Ball-switch duplex filter is an upgraded product.

Ball switching structure filter is composed of two high-flow single filters and a three-way-changeover ball valve in the middle.


There is a ball valve changeover and a contamination indicator that protects the hydraulic system safety and reliable sealing.

Characteristics of FilSon Ball-sealed Duplex Filter & Strainer:

  • Smaller in size:Compared to the traditional poppet valve structure, FilSon changeover ball valve duplex strainer is small in size, with compact structure. It requires minimal storage space for installation.
  • Lighter quality: Less volume and simple structure makes ball changeover duplex filter smaller and lighter.
  • Zero leakages:Cambered surface PTFE soft seal in ball-valve structure is more reliable and easy-to-operate than a hard seal of butterfly valve or cone valve. This eliminates the possibility of leakage inside the duplex filters.


In short, ball-switching structure is a reliable sealing, with a more convenient switching mechanism.

FilSon also offers large ball valve changeovers.

They can hold up to 7 high capacity elements per side.

Duplex Basket Strainer

Our duplex basket strainers can be manufactured in any shape or size to meet different industrial specifications.

2.FilSon Strictly Uses High Performance Filter Elements

duplex filter elements

Filter element is the core of this equipment.

All the other accessories and outer housing ensure normal operation of filter elements.

The performance of filter elements has a direct impact on the quality of the filter.

You can compare these two cartridges.

The difference is quite clear.

When the stitch welding and bonding craft is not good or, the filter material is of low quality, the strainer element may not effectively filter contaminants after a period of time when in use.

More leakage will make larger particles get away and return to the hydraulic system, resulting in higher operating costs and reduced functional life of equipment.

It is therefore appropriate to have strict control standards for raw materials and subsequent production processes.

Meanwhile, this alone is not enough; it should meet the required quality standards and laboratory tests.

Structural integrity of filter elements should conform to the GB/T20079, ISO 2942 test standards.

duplex filter test

Other tests include:

  • Fatigue tests that conform to GB/T 17488, ISO 3724 test standard.
  • Compatibility tests as per the ISO 2943, GB/T14041.1 test standard.


A cartridge with poor flow fatigue characteristics will damage the filter layer permanently.

As a result, the contaminated particles will bypass the downstream, thus affecting filtration capacity.

filter elements

For cartridges with poor compatibility, the filter layer easily falls off thus losing filtration characteristics.

This reduces the ability to contain pollution, hence, a major environmental concern.

A filter cartridge with good integrity

In short, a high quality filter element will ensure no internal leakage.

3.Advanced Welding Technique For A Smooth Duplex Filter Housing Surface

duplex filter welding manufacturing

Welding technique is the foundation of keeping “zero” leakage of duplex filters.

The choice of a welding process directly affects the quality and reliability of filter housing.

FilSon filter vessel welding does not have empty solder, leaking solder, wear due to soldering, head of welding wire of stomatic or burr, which may need polishing to keep the tube wall surface flowing.

filter polishing

Moreover, we also use the minimum number of welds for a smooth internal surface.

You can watch this video:

Welding video 2

Again, there is no bubble and trachoma produced in the operation.

It should meet strict quality standards and airtight testing, according to the GB/T 20079 requirements, for the finished duplex basket strainer to prevent oil leakage caused by inexperienced welding handle.

In short, this is an essential technology that can guarantee filter vessel “zero” leakage.

4.Proper Assembly Prevents Internal Oil Leakage

filter filter proper assembly

During duplex filter assembly, squeezing seals forcefully can either break or cut the edges of the seal.

Directional sealing elements fitted in the reverse may result in a twisted or squeezed out O-ring, which will cause seal failure.

As a result, unfiltered oil will easily leak through the cracks or holes on the seals.

Checking to ensure all ball seal O-rings are properly seated is a must.

Again, after a complete assembly of the duplex oil filter, it should pass the tightness self-test.

Here is an example: the seal between filter element and duplex filter housing is also through an O-ring.

O-rings can be installed either on the mounting seat of a cartridge or filter cartridges.

If you’re using damaged or inappropriate seal ring during the installation process, it will cause internal leakage in the duplex strainer.

Generally, by reasonable selection of O-ring, improving filter element chamber and installing disk seal position groove size solves the internal leakage problem.

Always ensure that the duplex filter air-tightness conforms to the GB/T20079 test standards.


Seal rings should be removed periodically. Normally, it should be done every time a filter element is replaced.

5.Adopt Top-Quality Material Of Sealing Elements

  • Compatible with working medium  

Additives, hydrolysis and redox reactions in the medium easily cause chemical corrosion.

As we all know, chemical corrosion may weaken the seal hardness, make the seal to expand or shrink excessively up to a point where it becomes completely destroyed.

Here is an example:

Poor working conditions or incompatibility with the medium increases hardness of the rubber or elastomer tensile strength becomes too high.

Top-Quality Material

Meanwhile, if the working medium of the hydraulic system deteriorates, it will corrode sealing elements.

Hence, we use high quality hydraulic fittings for quick set up and to minimize oil spills.

Besides, all sealing elements should pass laboratory test, according to the ISO 2943.

  • Adapt to temperature of the working environment

In hydraulic systems, too high or too low temperatures accelerate aging, hardening or deterioration or rubber seals. This results in loss of the sealing performance.

In addition to oil temperature of the system itself, external heat source also causes the local high temperature of the duplex filter.

Therefore, the location of the duplex basket strainer should be away from a heat source to prevent faster aging of the rubber seals.

This should be so, especially in steel mills and other working environments prone to very high temperatures.

6.Take Care Of Cleanliness Level of the Sealing Surface

Assembling components must be clean since it is a key factor that affects the overall hydraulic system.

This is critical, especially under poor working conditions where the pollutants or adhesion to sealing surface may cause sealing failure.

Some specific measures include:

  • Clean components before assembly
  • Pack and protect components before installation
  • Effectively remove new oil
  • Final clean before ex-factory


Surface Cleanliness Level

In general, there are many factors that affect the cleanliness of components.

These may include: types of component material, types of pollutants, the adhesion mechanism of the surface particles and cleaning methods used.

For pollution control, coarse cleaning is not enough.

It is just the first step in a comprehensive cleaning process.

The second step is to fine clean the surface.

That is, adopt effective cleaning steps such as using high purity solvents, tight control technology, highly accurate and effective test methods.

You should perform all cleaning operations in a clean environment.

Note: All duplex strainer components cleanliness should be specifically expressed via the ISO 4406 contamination level, in order to be consistent with the system cleanliness.

duplex filter ISO testing

7.Strict Selection Of Bypass Valve

Duplex basket strainers should be installed with a bypass.

This permits for bypassing the filter during element changes if the stream cannot be shut down.

When filter elements are heavily blocked, the bypass valve opens to ensure oil supply to the working system.

However, improper opening or shutting of the bypass valve may cause dangerous leaking that causes degradation or total failure in the filter.

For instance, when bypass valve’s design parameters are improperly selected or valve spool does not return due poor installation or manufacturing fault.

These problems can be detected easily by the ISO 16889/ISO 3968 tests.

Inspection result is manifested as:

  • Unable to form differential pressure
  • Abnormal filtering ratio

So, how do you choose a proper bypass valve for a duplex basket strainer?

It depends on the type of duplex strainers and filter elements.

To be specific, you should consider the systems’ working pressure, alarm pressure difference, requested filtration accuracy and oil pollution levels.

Meanwhile, some crucial performance practices of bypass valve include:

  • Accurate opening pressure
  • Good sealing after reset


Clearly, you can see that we have rich experience in the field of duplex filters and strainers manufacturing industry.

Our team has the know-how in the duplex structure, design, production arrangement and of course the assembly procedure of duplex basket strainers.

Even so, all FilSon duplex strainers meet the required quality standards and laboratory tests.

From raw material procurement, fittings management, production, installation, packaging, shipping to tracking.

FilSon has implemented an effective control in every aspect.

This guarantees “zero” leakage and prolonged safety of all filters.

Therefore, you can easily customize “zero” leakage filters that match exactly your industrial application requirements.

For more information or inquiries, feel free to contact us.

We have the know-how in duplex filter sealing control.