Oil Coalescing Filter: The Ultimate FAQs Guide

This guide answers all questions you have been asking about oil coalescing filters.

It covers everything including working principle, features, applications, material type, quality standards, and many more.

Let’s dive right in.

What is Oil Coalescing Filter?

An oil coalescing filter is a device you can use to remove oil droplets, aerosols, and particulates from an air stream or other fluid processes.

Oil coalescer filter

Oil coalescer filter

How does Oil Coalescing Filter Work?

Oil coalescing filters have small size fiber meshes that are suitable for amalgamating smaller particles into larger droplets.

The filter element has a filtration meshes of different sizes.

The inner meshes are finer while the outer meshes are course.

Filtration takes place from inside to outside.

As the process fluid moves through the meshes, the intersections facilitate the capture and amalgamation of the oil aerosols.

In the process, the smaller inner layers capture the solid contaminants, and the outer drainage layer facilitates the collection and drainage of oil aerosols.

For maximum filtration potential, the construction material should be non-absorbent nor non-adsorbent.

Once the outer layer has collected oil droplets, the force of gravity acts on the large drops and pulls them to the sump.

Generally, coalescing filtration removes the contaminants using three different mechanisms. These include:


  • This mechanism is responsible for the removal of the smallest of particulates contaminants below 0.1 microns.
  • It acts through the Brownian motion principle, where the particles collide with and stick to the filter element’s fibers.
  • The oil aerosols add to and join the other droplets to form large drops while the particulate contaminants adhere to the filter surface.


  • Interception acts through the principle of turbulent flow that affects particles suspended on the process fluid.
  • Filtration efficiency increase with reducing pore sizes as the particles turbulence forces the particles against the
  • Interception will facilitate the removal of particles between 0.1 to 1 microns.

Direct Impact:

  • This mechanism removes the most massive particles that are large than 1 micron.
  • Usually, the particles are too heavy to float on the process fluid. They drag along by the force of motion, hit the filter fibers, and stick on them.

What is the Function of the Oil Coalescing Filter?

Primarily, an oil coalescing filter removes oil contaminants from the air or gas stream.

However, an oil coalescing filter will also remove other particulate pollutants such as dirt, dust, pollen, etc.

The oil coalescing filters reduce possible downstream corrosion, blockage, wear and tear, and contamination by removing them.

It will enable you to achieve the desired level of product purity required by your process application.

Removing impurities will also help you minimize the downtime costs associated with wear and tear, which cumulates into reduced operational and maintenance costs.

Why should you Remove Oil from your System?

Liquid oil and oil vapor can be very harmful to your system.

These contaminants will cause premature damage to system components such as valves, pumps, and seals sensitive to oil.

Oil can also cause havoc and disruption when it finds its way into the engines.

As such, it will significantly affect the overall performance and reliability of your system.

Henceforth, you will experience increased breakdowns and downtimes that translates into low profit and high losses.

Consequently, the oil coalescing filter provides an extra level of protection that goes a long way to ensure minimal replacement and maintenance.

What are the Features of a High-Quality Oil Coalescing Filter?

A high-quality oil coalescing filter should possess the following key features:

Oil Coalscer filter system

Oil coalescer filter system

  • Resistant to corrosion and chemical degradation
  • Achieve the rated filtration efficiency at the specified micron rating
  • Have multiple options for drainage to select from
  • Available for use over a wide flow rating, pressure, and temperature
  • High filtration efficiency
  • Possess stable structural components that can withstand demanding filtration conditions
  • No media migration nor fiber shredding
  • Environmentally friendly
  • Compatible with various fluids

Why use Oil Coalescing Filter?

Oil coalescing filter is a fundamental device in applications requiring the removal of liquid oil and oil aerosols to protect sensitive system components.

You will immensely benefit from the following advantages as a result of installing an oil coalescing filter.

  • The filter is constructed using high-density and high-quality materials that ensure stable, high performance, and reliable filtration elements.
  • Robust construction using top quality materials ensure attainment of maximum product filtration. Using our filters will enable you to remove up to 99.99% of oil contaminants down to 0.01 particle size.
  • The filter elements have optimal designs and configurations that will enable you to save energy by maintaining a low-pressure drop and production costs.
  • It is compatible with a wide variety of materials due to its anti-corrosive nature, making it suitable for diverse industrial applications.
  • Low maintenance costs.

Which Applications Require Oil Coalescing Filter?

You can use an oil coalescing filter in a wide range of applications spread over diverse kinds of industries.

Primarily, oil coalescing is mandatory in oil and gas or petrochemical industries.

In compressed air filtration, oil coalescing filters are fundamental for the recovery of compressor lube oil downstream.

You can also use an oil coalescing filter to remove other hydrocarbons and water from natural gas in the petrochemical, oil, and gas, and oil refining industries.

In the case of oil-liquid coalescer, you can use it to:

  • Clean caustic and water from an online analyzer sampling system
  • Separate water and oil in wastewater management
  • Separate hydrogen peroxide working solution and water or hydrogen peroxide

Other industries that can benefit from the use of oil coalescing filter are:

  • Wastewater management
  • Chemical processing
  • Airports
  • Tram oil
  • Pulp and paper industries
  • Spillage recovery operations
  • Automotive and motor vehicle system
  • Shipping industries
  • Aeronautical

What are the Components of Oil Coalescing Filter?

The inclusions of an oil coalescing filter may vary depending on the type of application for use.

A standard oil coalescing filter for industrial use comprises the following key components:

Oil coalescing system

Oil coalescing filter

  • Inlet: Allows the entry of dirty and oil contaminated fluid
  • Outlet: Used for removal of dry, cleaned air/gas/fluid
  • Sump: Holds or collects the coalesced oil and water
  • Housing: Holds the elements, ports, and other components in place.
  • Element: Coalesces and amalgamate the liquid and oil aerosols then drain them down the sump
  • Drain: Used to remove the contents of the sup
  • O-ring: Seals the grove between the filter bowl and the head
  • Differential pressure gauge: Indicates the pressure differentials of the filter element.

Which Material is Oil Coalescing Filter made of?

You can select from the wide variety of materials that are ideal for constructing high-quality oil coalescing filters.

You can use either of the following materials:

  • Fiberglass
  • Borosilicate glass micro-fibers
  • Lattice
  • polypropylene
  • Synthetic polyester fibers etc.

To enhance filtration efficiency, you can treat the filtration fiber mesh’s surface with an oleophobic or hydrophobic material.

The treatment will ensure that you meet the desired filtration precision by lowering energy on the filter surface and increasing the coalesced liquid’s drainage speed.

Surface treatment possesses the following benefits:

  • Reduced pressure drop
  • Reduced assembly sizes
  • Higher liquid challenge capacity
  • Ease of recovery from liquid slugs

You should construct the element from multiple mesh layers of varying sizes and properties.

The shape, thickness, size, and density of fibers used to construct individual layers should be different to achieve precise filtration needs.

What should you Consider when Choosing Oil Coalescing Filter?

Selecting an appropriate oil coalescing filter is mandatory for satisfactory filtration performance.

Ensure that you consider the following factors to get the best out of the oil coalescing filter.

· Material of Construction

The material of construction should be compatible with the processing fluid and the contaminants you are filtering out.

It should possess the coalescing ability for the efficient removal of liquid oil and oil aerosols.

· Operating Conditions

Here, it would be best if you considered your system conditions before settling for a specific filter.

Ensure that the filter you select is capable of withstanding maximum pressure, temperature, and flow rates.

It should also be ideal for minimum system flow rates, temperature, and pressure without lagging the production process.

Sometimes the locality of filter installation is harsh, that is, saline, acidic or alkaline.

Under such conditions, you can go for the most suitable construction material like metal alloys to withstand stress.

· Drainage

You can either select an oil coalescing filter with an automatic or manual drainage system.

You will have to manually unscrew the manual drains periodically to remove the wastes in the sumps.

Contrastingly, the automatic drains will detect and release the contents periodically when the sump contents have reached the pre-set level.

Consequently, an automatic drain system is preferred because it requires minimal supervision and hence reduced labor costs.

However, the automatic systems also come with the potential for failure, which can be very costly when not detected on time.

· Desired Product Cleanliness

Oil coalescing filters come in different micron ratings and suitable for diverse kinds of applications.

You should select a filter with the most appropriate micron rating to balance effective filtration and pressure drop.

Fine-sized filter elements always give `the highest filtration efficiency and pose a considerable barrier to the fluid flow, that is, high-pressure drop.

· Dirt Holding Capacity

Again, depending on the flow rate of your system and dirt load of the incoming fluid, you can select the most appropriate filter with sufficient dirt holding capacity.

Usually, the dirt holding capacity corresponds to the size of the filter.

Pleated designs also have a higher dirt-holding capacity compared to depth filters.

How long will Oil Coalescing Filter Last?

Through time, the filter’s filtration efficiency starts depreciating due to the pile-up of dirt in the filtration medium or wear and tear.

Depending on the type of use, dirt load of the incoming fluid, and frequency of use, the oil coalescing filter can serve either for months or years.

For less sensitive applications like the refrigerator’s compressor system, the coalescing oil filter can take up to 3 years of the service life of 15 000 hours.

For heavy-use applications, you should frequently check on the filter’s differential pressure and schedule changeover appropriately.

Notably, it would be best if you changed the filters at least once in a year or wash it in the case of cleanable filters, with or without the attainment of its change-out differential pressure.

Can you Clean Oil Coalescing Filter Housing?

Yes, you can clean the oil coalescing filter housing using appropriate detergents and cleaning techniques.

Which Factors Affect the Performance of Oil Coalescing Filter?

The performance of a coalescing oil filter depends on the filtration efficiency and pressure drop.

These two key factors are highly dependent on the operational conditions, filtration media properties, and oil properties.

These factors include but not limited to:

  • Fluid velocity
  • The concentration of the oil droplets and aerosols
  • Liquid loading rate
  • The surface tension of the oil
  • Oil viscosity
  • Micron rating of the filter element
  • Size and distribution filter fiber pores
  • The wettability and average packing density of the filtration material
  • Structure of the filtration element
  • Size of the filtration element
  • The properties of the filtration media

How do you Optimize the Efficiency of Oil Coalescing Filter?

You can use different methods to improve the performance of a coalescing filter.

These methods should concentrate on the filtration medium and operational conditions.

Some techniques that you can use include:

· Increasing Fluid Velocity

Increasing the contaminated process fluid’s velocity to optimum also increases the momentum and fluid and its contaminants.

A rise in momentum increases the probability of a coalition between the medium fiber and the oil droplets/ aerosols.

· Reducing the Operating Temperature

Because heated fluids hold more contaminants, lowering the operating temperatures will significantly reduce the process fluid’s dirt holding capacity.

The gas stream will readily shed excess oil droplets upon lowering the temperature.

· Using a Smaller Pore-sized Filter Media

Reducing the pore size of the filter media enhances the capture efficiency of the coalescing oil filters.

Coalescing oil filters with fine-sized pore media provides a tortuous path, ensuring that the oil aerosols do not escape collision with the fibers.

· Reducing the Viscosity of Process Fluid

Decreasing the fluid’s viscosity reduces the settling time of the droplets by lowering the drag force of the process fluid.

You can achieve the reduction through increasing the operating temperatures to optimal levels that do not inhibit separation.

How do you Specify Oil Coalescing Filter?

You can specify an oil coalescing filter by counter checking the product catalog.

Counterchecking against the product specification will help you ensure the filter grade you are ordering meets all your process requirements.

When should you Change Oil Coalescing Filter Cartridge?

You can replace your coalescing oil filters when it has reached the recommended change-out differential pressure.

Usually, the change-out pressure varies from 8 to 10 PSI.

You can perform between 4 and 5 cleaning cycles for a cleanable oil coalescing filter before replacing the elements.

Beyond the fifth cleaning, the cost of cleaning may not be profitable.

The filter housing can last for more than 25 years, depending on the material of construction, use, and maintenance.

What Designs of Oil Coalescing Filters are there?

Oil coalescer filter system

You can get oil coalescing filters in different designs and configurations.

The housing structure can be vertical or horizontal.

The choice of configuration will depend on the preference and requirement of your system.

You can also get housings that are either duplex or simplex configuration.

What Types of Oil Coalescing Filters are there?

There are two main types of oil coalescing filters.

They include:

· Oil-liquid Coalescing Filter

It is an oil liquid separator, and you can use it in applications like oil recovery or wastewater management.

It will separate oil and any other liquid with a different density and does not mix with it.

· Oil-air/gas Coalescing Filter

This air-oil separator is ideal for use in applications such as purification of natural gas or compressed air.

It removes oil aerosols and liquid oil from air or gas, thus delivering a high-quality, dry gas.

How do you Choose the Design for Oil Coalescing Filter Housing?

Designing housing for your oil coalescing filter is just as crucial as selecting the right filter elements.

Design considerations mainly depend on the system requirements and should be ideal for optimal filtration needs.

Initially, you may wonder what configuration to select between vertical and horizontal design.

You should note no significant functional differences between the two designs, but the suitability for use will depend on how it aligns with other system components.

Vertical housing is ideal for applications that have limited floor space for installation.

On the other hand, you can use horizontal housing in places where the installation space is not limited because it covers a large floor area.

However, horizontal housing configurations can support higher flow rates compared to vertical housings.

They will also confer the least pressure drop to fluid flow when installed online, unlike the vertical housing designs.

You can also opt for duplex or simplex housing designs.

A duplex housing is a pair of simplex housings that have interconnected for ease of element interchange.

You can use duplex designs in continuous applications that cannot stop for coalescing filter element replacement.

They offer you an easy and fast change-out and maintenance without costly downtime operations.

On the contrary, you should select a simplex design when dealing with batch applications, which you can stop for filter element change-out.

They are simpler and cheaper, making them economically ideal for simple operations.

What are the Quality Standards for Oil Coalescing Filters?

Your oil coalescer filter should meet both the requirements of ISO 8573 and ISO 12500.

ISO 8573 are compressed air quality standards that ease the selection, measurements, and designs of filters, including oil coalescing filter.

The first part of 8573 defines the classes and types of contaminants and assign them to different quality classes.

The other parts, 2 to 9, describe the test methods you use to determine the full range of pollutants in the filtered air.

You will present the air quality test data as per ISO 8375:1:2001 table in which the first section or class A shows solid particle.

Class B depicts humidity and liquid water, while class C designation is for Oil contaminants.

On the other hand, ISO 12500 standards specify methods for testing the performance and rating the compressed air filters.

Oil aerosol removal efficiency of coalescing filters are addressed in the first part of ISO 12500.

The second part of the standards specifies how to test for removal of oil vapor while the third part gives guidelines on how to test for removal of solid/particulate contaminants.

Can you use Oil Coalescing Filter as Pre-Filter?

Yes, when the situation dictates, you can use it as a pre-filter to downstream desiccant or adsorption filter.

Are there Self-cleaning Oil Coalescing Filter Systems?

Yes, you can get an automatic self-cleaning filter when you don’t want to manually clean the elements or your application demands a continuous process.

The differential pressure will transmit a signal to the control system upon attainment of pre-set differential pressure.

The control system then initiates an automatic cleaning system that removes the entrained particles through buck flushing.

How does Oil Coalescing Filter compare to Standard Filter Systems?

The standard particulate filter system can only remove particulate contaminants from the filtration fluid.

Even in standard coalescer, the filtration media is not specially designed and treated with materials capable of collecting and draining oil aerosols.

They lack unique materials and treatments required for efficient removal of liquid oil and oil aerosols.

On the other hand, the surfaces of individual layers of oil coalescing filters contain special treatment that is ideal for removing oil aerosols.

Oil coalescers will also remove other dirt, dust, and water drops from the compressed air.

Oil coalescing filter will meet the specifications of ISO 8573-1 standards.

This requires filters to remove oil aerosols down to 0.01 mg/m3 and particulates down to 0.01 microns.

Any standard filter cannot achieve these specifications.

At FilSon Filters, we offer highly efficient oil coalescing filters.

Contact us now for all your oil coalescing filter replacements.

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