What is an FRL?

What is Pneumatic FRL?

Pneumatic FRL is also called Air source treatment or Air preparation units. An FRL combines a filter(F), regulator(R), and lubricator(L) (2 or 3 of them) into one component to keep air compressor systems in optimal working condition. Each of these individual components has its role, supporting the larger air compressor system.

  • Filters remove water, dirt and other harmful debris from an air system.
  • Regulators adjust and control the air pressure of a system to ensure that down-line components do not exceed their maximum operating pressures.
  • Lubricators reduce the internal friction in tools or equipment by releasing a controlled mist of oil into the compressed air.

Why is an FRL needed and how do they work?

In pneumatic systems, contaminated air leads to premature wear in valves and cylinders, attacks seals and causes them to leak, results in rust and corrosion in tools and piping, and is generally the root cause of faster breakdowns and higher maintenance and operating costs. Also, the air supplied by compressors is often over-pressurized, and non-lubricated, if left untreated, it can damage products and shorten the life of downstream equipment.

Thus, air needs to be filtered, cooled, dried, regulated, and lubricated before it can be used.

We will introduce the filter, regulator, and lubricator separately as below.


Filters are used to remove contaminants. The filtration is achieved at various locations in the system.

  • At the intake of the compressor that takes in outside air.
  • At the outlet of the compressor tank from which air for the system is obtained as shown on the diagram.
  • At the input of some pneumatic-driven machines to remove contaminants that are picked up as air flows through the distribution network.


The pressure regulator is a special type of valve. A pressure regulator has two functions:

  • To adjust the supply pressure to the desired level for downstream pneumatic equipment to operate most efficiently: In most situations, the pressure level of the air supply from the compressor is too high for the components in a pneumatic system. The regulator has a knob that can be turned to adjust the air pressure to a suitable level.
  • To maintain constant air pressure in the system: The pressure of the air in a pneumatic system can fluctuate. The pressure fluctuations can be caused by air being exhausted from the compressor tank into the system or when the tank is replenished by the compressor.

Regulators have a control spring that acts on a diaphragm to regulate the air pressure. The rating of this control spring determines the pressure adjustment range of the regulator. As the pressure from the outlet port increases, the air pushed the diaphragm upward against the spring. The pressure setting of the regulator can be changed by varying the compression of the main spring with the adjustable knob.


A lubricator adds controlled quantities of tool oil into compressed air once it’s been cleaned and regulated to reduce the friction of moving components and protect the downstream components against friction. Lubricators will require maintenance to re-fill the oil reservoir when it becomes low and can be monitored through the sight glass or a window located on the housing. Lubricators also require a pressure differential to make the oil drip, therefore, they create a pressure drop at the outlet. This needs to be taken into account to ensure the proper pressure reaches the end component. This means that air will not be lubricated if the system is off, which allows for no oil waste. It should be noted that many pneumatic components are self-lubricating and don’t require any additional lubrication.

How to choose FRL?

Filters, regulators and lubricators can be offered individually or as a combined filter-regulator (FR) or filter-regulator-lubricator (FR/L or FRL) unit(As the figure below). It is recommended to install an FRL or FR/L unit if your equipment requires lubrication and an FR unit if your equipment is self-lubricating.

The type of FRL components required is dependent on your system requirements, but it is recommended that every air system uses at least one filter and one pressure regulator.

As a general rule, the order of installing them is like this: compressor->filter->regulator->lubricator.

Besides, there are several factors to consider when you choose the FRL unit.

  • FRL Materials: You need to choose FRLs made of metal if the working environment is with extreme heat or cold, chemicals or salt. Or else you can use FRL made of composite materials.
  • Airflow: Choose an FRL whose airflow capacity is greater than the tools you are going to use.
  • Port sizes and thread sizes: The FRLs you choose for your air system need to be with the right thread and sizes. Or else, they will become a pile of waste.

Pneumatic filter selection

There are several different types of filters to choose from, General-purpose pneumatic filters are designed to remove solid particulate contaminants such as dust, dirt, pipe scale and rust, and separate out liquid water and water droplets. Coalescing filters remove oil aerosols, and activated-carbon filters remove oil vapor. Choosing the wrong filter or applying the right filter incorrectly can do greater harm than good.

There are 3 important factors:

1. Micron size: 

Particle-removal filter elements are rated by the size of particles they trap. For example, if you have a 20-micron filter it will allow particles smaller than 20 microns to pass through. 40 microns or 5 microns filters are usually used as standard general-purpose filters in industrial applications. A 25-micron filter is another choice if needed. However, higher-efficiency filters are also available to remove even smaller particles—1 micron or less in some applications, such as food, beverage, and pharmaceutical applications.

But pls note, it does not mean the finer micron the better, a 0.1-micron filter will create a larger pressure drop than a 40-micron filter and will require more regular maintenance due to the easy buildup of contaminants.

2. Drainage type: 

There are 4 drainage types you can choose: automatic, semi-automatic, manual and condensate drain type.

3. Flow capacity: 

After your engineers understand the required flow for a pneumatic application, select the proper-size filter by determining the maximum allowable pressure drop across the filter.

The pressure drop can be determined by referring to flow curves provided by the manufacturer.

Pneumatic regulator selection

There are 3 types of pressure regulators:

1. General purpose regulators

they are designed to give the maximum flow capacity, and maintain the outlet pressure at a set level to a reasonable accuracy. They operate due to a control spring acting on a diaphragm to regulate the air pressure. Outlet pressure is determined by turning the knob clockwise or anti-clockwise to increase or decrease pressure. General Purpose regulators are available in relieving and non-relieving types.

2. pilot-operated regulators

Instead of being regulated by a control spring, the outlet pressure in a Pilot Operated regulator is controlled by an air pilot signal. Pilot Operated regulators generally have better regulation than General Purpose regulators.

3. Regulators specific to the application

they are needed when some applications are with specific characteristics.

Downstream equipment flow and pressure requirements must be determined to properly size the correct regulator for the application.

You need to choose a pressure regulator with a higher maximum pressure to prevent damage when the system is over-pressurized.

Pneumatic lubricator selection

Many pneumatic components are self-lubricating and don’t require any additional lubrication. But still, lots of components need lubricators to reduce the internal friction.

Lubricators are generally selected based on pipe connection size, oil reservoir capacity, and allowable pressure loss versus flow rate.

They are sized by downstream flow requirements. An analysis of airflow use must be made. After determining how much airflow is needed, a lubricator can be chosen.



Hi, I’m Zoe, I like sharing knowledge of related pneumatic and automatic products, also, some useful skills. Hope we can learn from each other.
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