Compressed air leaving a compressed air system can be hot and full of contaminants like dirty and water vapor. This can damage and certainly shorten the lifespan of the downstream equipment which includes in-line valves and your pneumatic tools.

This calls for the requirement of the compressed air to be cleaned and lubricated. That’s where an FRL comes in!

Table of Contents

What is an FRL?

An FRL is a combination of a filter, regulator and lubricator that are all together in-line on your air compressor system in order to keep the air flow in your air line and reaching your air tools at its optimum condition.

Please note the order of the letters in the acronym F-R-L. The letters are in this order on purpose.

First comes the Filter, then the Regulator and then the Lubricator. Putting the lubricator before the filter will simply fill the filter bowl with oil, and none will get downstream. You don’t want oil flowing through your regulator either, so the lubricator should always be downstream of the regulator which is always installed after the filter so that clean air can flow through that device too.

You’ll typically find them located at the specific drops or workstations just before the connection with the air tool is made as can be observed in the example schematic below.

Typical Work Station Schematic

Compressed air is clean, readily available and simple to use! However, unregulated or improper pressure settings can result in increased compressed air demand and thereafter an increase in energy consumption.

Excessive air pressure can damage equipment, resulting in higher maintenance costs and a shorter lifespan. Point-of-use FRLs are needed to ensure that every pneumatic tool or device attached at the end of the line receives a clean lubricated supply of compressed air at it’s optimum pressure.

As you may have grasped already, a FRL consists of the three primary components that each play an important role in supporting the larger air compressor system. These components are:

  • Airline Filter
  • Pressure Regulator
  • Lubricator

Now let’s look at these in greater detail!

Airline Filter

First in the FRL configuration is the airline filter. This works to clean the compressed air of any particulates that are trapped within the air before reaching the regulator.

These particulates include dust, dirt and rust from within the pipe. An air line filter also helps separate water and oil entrained in the compressed air so that the pneumatic tools get the highest purity of air as possible.

The air filters are commonly found upstream from regulators, lubricators and the air driven devices for the sole purpose of filtering the air flow.

As airline filters remove contaminants from pneumatic systems, they’re able to prevent damage to pneumatic tools and reduce possible production losses due to contaminant-related downtime. Downtime is expensive and is certainly desirable to avoid by maintaining the compressed air system to a high standard.

When selecting a filter size for your air compressor system, it should be done by determining the maximum allowable pressure drop across the filter, which can be determined by referring to the flow curves provided by the manufacturer.

There typically tends to be 3 main types of compressed air filters that are used on air compressors to ensure the air exiting the system to your desired tools at its purity requirement. These types ultimately produce the same result however operate on slightly different principles.

The three types of compressed air filters are:

  • Coalescing filters
  • Vapor filters
  • Dry particulate filters

Knowing what the needs of your compressor are before choosing your air filter can help ensure you choose the right one.

Coalescing Filters

Coalescing filters are capable of handling very fine particles that in some cases can as small as 0.001microns. They are able to remove particles such as aerosols, water, oil, and other liquids however, they cannot catch vapors.

Vapor Filters

Vapor removal filters, or also known as, activated carbon filters are typically used to remove the vapors/gaseous lubricants that go through the coalescing filters.

Vapor filters must be placed after coalescing filters as they cannot capture aerosols due to their absorption process which would allow the aerosols to saturate the filter.

The activated carbon inside the filter provides a broad surface area that naturally attracts oil vapor onto it and away from the air stream.

Dry Particulate Filters

Dry particulate filters operate in a similar manner to coalescing filters by capturing and retaining particles within their filter units. They particularly target dirt, dust and other similar fine particulates like rust from corrosion inside the compressor unit.

For more information on air filters please visit our Compressed Air Filtration Guide – Types of Filters & Their Purpose guide, and for information on Filter Bowls For Compressed Air comparison page!

Air Pressure Regulators

Air pressure regulators, or otherwise known as pressure reducing valves, are used in compressed air systems to reduce and control the primary pressure in the airflow.

When at its optimum, air pressure regulators maintain a constant output pressure regardless of the variations in input air pressure and downstream equipment flow requirements.

Air pressure regulators are used to control pressure to a whole variety of pneumatic tools, and typically are available as either types:

  • Relieving
  • Non-relieving

Relieving type regulators allow for high pressure to be adjusted to low pressure even in dead-end situations. They relieve the excess downstream pressure into atmosphere, causing a loud hissing like sound that you’ll be able to here.

On the contrary, non-relieving valves do not allow the excess downstream pressure to be relieved into atmosphere… but you need to still release this trapped air somewhere right? Therefore, a downstream valve would need to be introduced.

To correctly size a regulator for your desired applications, the downstream equipment flow and air pressure requirements must be determined.

For more information on Air Compressor Regulators – Principles, Types & Video Guide please visit our page!

Air Line Lubricators

Air line lubricators are devices used to provide lubricant to a compressed air operated air tool or compressor air driven equipment. They add controlled amounts of tool oil into the compressed air system in order to reduce the friction of moving parts inside the air tools or other pneumatic devices.

They do so by being installed either at the outlet from the air compressor as part of an filter regulator lubricator system, or further along the air plumbing near the equipment needing added lubrication.

In the top housing of the lubricator will be an adjustment screw, turning this will increase or reduce the frequency of drops of lubricating oil allowing you to provide accurately metered quantity of lubricant to the air-operated equipment.

Airline lubricators typically come in one of the two types:

  • Oil-Fog
  • Micro-Fog

Oil-fog lubricators are used in heavy applications, such as single tools, cylinders and valves whilst micro-fog lubricators are used for multiple applications, sever cylinders or valves.

All the oil droplets visible in the sight dome of oil-fog lubricators are added directly into the air flow as relatively large oil droplets passing downstream. In micro-fog lubricators however, the visible oil droplets are atomized and collected in the area above the oil in the bowl. It is said around 10% of the sighted oil drops are light enough to be drawn into the air flow and passed downstream.

Many air valves and air cylinders come from the factory already well lubricated. It’s only in really high cycles that lubricant may need to be added. Check with the cylinder or linear slide manufacturer for lubricating requirements for their tool. An error will lead to unnecessary maintenance issues before their normal life cycle would otherwise indicate.

If a lubricator is installed in an air line feeding items that are already factory lubricated, it will result in the new oil washing out the factory lube, and from then on, you will have to continuously provide external lubrication for the lifespan of the item.

Therefore, it is important to check with the vendor of that air tool or component to be sure if it needs additional lubrication.

An analysis of air flow must be conducted to determined downstream flow requirements before choosing a lubricator size.

Choosing a FRL Unit (Filter-Regulator-Lubricator)

Choosing the right FRL unit for a compressed air system is a very important consideration. Do you want to individually choose your pneumatic filter regulator lubricator, or buy a combination unit?

Application Specification Considerations

Before selecting a device, it is extremely important to know the pressure, flow rate and air requirements of the pneumatic tools using the compressed air, as well as if any air quality standards apply to your workspace before selecting your unit or component.

To ensure that your FRL unit or individual components meet the pressure ranges in and out the flow rate requirements, consult the datasheet of the specific unit.

Consider the environment that the device will be installed in and exposed to, as you can select specific housing materials to suit your environment. Nylon or polycarbonate housing is typically acceptable for most general applications whilst metal housing should be used if it is to be installed outside, or exposed to heat, salt or chemicals.

Air Filter Selection

Reliability is one of the most crucial reasons to use compressed air, and therefore efficient filtration is absolutely vital in maximizing this reliability and longevity. Contaminant particle size is measured in micrometers which each represents one-millionth of a meter.

Filters are rated according to the minimum particle size that their elements will trap, the finer the filter rating, the higher the pressure drop through the filter, which will equate to higher energy costs.

Finer filters also clog far more rapidly, and this clogging will cause an increase in pressure drop. Most filter manufacturers will define the pressure loss expected and dirt holding capacity of filters using curves that relate to pressure and flow… so, it is vital that you select your filter based on acceptable pressure drop and pipe connection size.

Air Pressure Regulator Selection

Selecting the best type of regulator for specific applications first depends upon the style of regulator. You have poppet-style valves, or ones with diaphragm chambers. Most standard regulators tend to be relieving separate-diaphragm-chamber style.

Deciding your style must then be followed by taking consideration into the primary unregulated supply of air pressure versus your desired secondary output air pressure before moving on to selecting your desired airflow.

Although several models may appear to be suitable for any given pressure and flow characteristics, a larger regulator body size will typically produce better setting sensitivity and less droop than a smaller body size when operating under the same conditions. Ensure an output pressure gauge is attached.

Air Line Lubricator Selection

Lubricators more commonly than not have a larger flow range than an equivalently sized regulator or filter, however their pressure drop increases significantly as flow increases.

Lubricators are typically selected based on the pipe connection size, oil reservoir capacity, and the allowable pressure loss versus flow rate. Most manufacturers will provide a minimum flow rate at which the venturi will function properly.

Note: It’s important to account for the lubricator pressure loss when setting the pressure regulator.

FRL Combination Unit Selection

Manufacturers are consistently offering preassembled configurations of filters, regulators and lubricators for ease of insertion into compressed air systems. These combination units come packaged together as standard body sizes with common connection port sizes.

The modular connectors allow for easy removal of components so that they can be serviced and cleaned. It’s also possible to just get FR combinations where your tools don’t need lubricating or are self-lubricating. These compact stacked assemblies feature the filter head becoming the regulator body, allowing them to share common inlet and outlet connections.

These combination units are a practical choice for most industrial applications. The selection must involve combining the pressure and flow performance. Though it is possible in special situations to pick specialty filters or precise regulators and make up a combination using pipe nipple connections.

An example of an FRL combination unit is provided below and is one, amongst many, readily available to buy on Amazon.

FAQs (Frequently Asked Questions)

Do I need a filter regulator lubricator?

It is important to understand the air requirements of your air compressor system and components to know if and what components of an FRL unit are needed.

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!

Most modern day pneumatic tools are self-lubricating so you may not need a lubricator, and instead just install an “FR”.

Do I need an air lubricator?

You’ll need to check with your air-driven applications, as these may already have self-lubrication that can last their whole lifespan. So it’s important to not plumb a lubricator into your air supply before checking your air tools!


If you have any questions regarding FRLs on air compressors, then please leave a comment below, with a photo if applicable so that someone can help you!