What is an FRL Unit- Filter Regulator Lubricator

The hot, dirty, and wet air leaving a compressor can damage and shorten the life of downstream equipment, such as valves, cylinders, and air tools. Before compressed air exits the system, it must be cleaned and lubricated. This is where an FRL Units comes in! To keep air compressor systems functioning optimally, an FRL combines a filter, regulator, and lubricator.

FRL Unit Components

An FRL has three primary components:

  • Airline filter 
  • Pressure regulator
  • Lubricator

In support of the larger air compressor system, each of these components plays a separate role. We will discuss these roles in the following sections.

Airline Filter

Air is cleaned by an airline filter. The air is strained, solid particles (dust, dirt, rust) are trapped, and liquids (water, oil) entrained in the compressed air are separated. Filters are installed in the airline upstream of regulators, lubricators, directional control valves, and air-driven devices such as air motors and cylinders.

FRL Unit System

Airline filters remove contaminants from pneumatic systems, which reduces equipment damage and production losses associated with contaminant-related downtime. Compressed air systems that are contaminated and poorly maintained are commonly the cause of downtime.

Types of Air Filters

Three types of air filters are common in FRL Unit Systems:

  • General purpose
  • Coalescing (oil removal)
  • Vapor removal 

pneumatic filter

General-purpose filters remove water and particles, coalescing filters remove oil, and vapor removal filters remove odors and oil vapor.

Pressure Regulators

Air pressure is reduced and controlled by regulators in compressed air systems, including rotary screw air compressors. Regulators are often referred to as PRVs (pressure reducing valves).

Despite variations in the input pressure and downstream flow requirements, pressure regulators should maintain a constant output pressure. The output pressure is affected to some extent by variations in the primary pressure and flow.

Pressure regulators are used to controlling: 

  • Air tools
  • Blowguns 
  • Spraying devices
  • Fluidic systems
  • Air logic valves
  • Aerosol lubrication system
  • Most other fluid power applications 

Regulators can be relieving or non-relieving. Relief regulators can be adjusted from high pressure to low pressure. In spite of a dead-end situation, relieving regulators will allow excess downstream pressure to be exhausted. The pressure relief causes a loud hissing sound, which is perfectly normal.

Similarly adjusted non-relieving regulators will prevent downstream pressure from escaping. The trapped air will have to be released in some other way for example, by opening a downstream valve.

In order to size, the correct regulator for the application, downstream equipment flow, and pressure must be determined.


Lubricators reduce friction between moving components by adding tool oil to compressed air systems. Lubrication increases the useful life of air tools, cylinders, valves, air motors, and other air-driven equipment.

Airline lubricators solve the problem of too much and too little lubrication that can occur with conventional lubrication methods such as a grease gun and oil. Additionally, airline lubricators supply the right kind of lubricant for the tools.

An accurately metered quantity of lubricant is supplied to the air-operated equipment after the lubricator is adjusted. Periodic refilling of the lubricator reservoir is the only maintenance required.

Lubrication also washes away compressor oils that travel through a system in vapor form. Mineral oils added to the system prevent synthetic compressor oils from building up on system components. To remove compressor oil aerosols when lubricators are not used, a coalescing filter should be installed.

Lubricators are sized according to downstream flow. An analysis of airflow use is therefore necessary. Depending on how much airflow is required, a lubricator can be selected.

Types of Airline Lubricators

There are two types of airline lubricators

  • Oil-Fog
  • Micro-Fog

There are two kinds of air lines: Oil-Fog and Micro-Fog. Oil-Fog uses a pipe that is big and thick so the oil can’t get out. Micro-Fog uses a pipe that is small and thin so the oil can get out.

All oil droplets visible in the sight dome are added directly to the airflow, resulting in relatively large oil droplets passing downstream. The oil droplets visible in the sight dome of a micro-fog lubricator are atomized and collected above the oil in the bowl. The smaller, lighter particles are drawn into the airflow and are carried downstream. Therefore, only 10% of the visible oil drops in the sight dome are passed downstream.

How To Choose The Right FRL Unit For Compressed Air Systems

In your application, compressed air is clean, readily available, and easy to use, although it can be the most expensive form of energy. An unregulated or improper pressure setting can result in increased compressed air demand, which results in increased energy consumption.

Additionally, excessive pressure can result in increased maintenance costs and shorter tool life. Compression energy costs increase by 1% for every 2 psi increase in operating pressure.

A point-of-use FRL (filter, regulator, and lubricator) ensures that every tool or process receives clean, lubricated compressed air at the right pressure to maximize efficiency.

Choosing A Filter For Compressed Air 

One of the main reasons to use compressed air is its reliability, and the key to maximizing reliability and longevity is proper filtration. Sadly, compressed air can carry condensed water, oil carryover from compressors, solid impurities (pipe scale and rust) generated within pipelines, as well as other wear particles from the ambient air. Filters are necessary to remove contaminants at every point of use since they can cause problems.

Furthermore, finer filters clog more rapidly, resulting in a higher pressure drop. (In other words, finer filters do not harm downstream components, but they negatively impact air system operating costs.)


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