In a hurry? These are the things you need to know:

• An FRL unit combines filter, regulator, and lubricator in a single housing. For most workshop applications with impact wrenches and similar tools, this is the straightforward choice.
• Not every tool needs lubrication. Spray guns, digital tyre inflators, and some spray equipment run oil-free — adding a lubricator will contaminate the finish or damage the tool. Check the manufacturer's spec.
• Filtration level matters. General air tools need 10-micron filtration; spray painting and food applications need 5 micron or finer. Don't over-specify — a finer filter than needed increases energy consumption and pressure drop.
• Size the unit to the flow rate, not just the port size. An undersized air treatment unit restricts airflow and effectively throttles the whole system.

Running a compressor without air treatment is a false economy. Moisture, particulates, and uncontrolled pressure shorten tool life, corrode pipework, and ruin spray finishes. The question is which components your system actually requires.

Most workshop setups use an FRL unit: a single assembly that combines a filter, regulator, and lubricator. It mounts inline between the compressor outlet and the first tool connection, treats the air once, and protects everything downstream. Individual components are also available if you only need part of the function.

This guide explains what each component does, when you need it, and how to size the unit to your system.

The benefits of using an air treatment unit

Do you really need to use an air treatment as part of your compressed air system?

You may be tempted to save on the cost, but in the long-run you’ll be worse off.

Why?

Because without an air treatment unit, your system will be running on unregulated, unlubricated, unfiltered pressurised air.

As we mentioned at the outset of this article, this will increase wear on your equipment, reducing the lifespan of your tools and ultimately leading to you having to shell out more money for tools and equipment.

Not using an air treatment unit is a false economy.

What are the different types of air treatment units?

When it comes to selecting an air treatment unit for your compressed air system, you have a number of different types to choose from:

• Air filter unit
• Air regulator unit
• Air lubricator unit
• Units that include a filter, regulator and lubricator (or variation thereof)

Depending on what you’ll be using your compressed air for, and how regularly you’ll be using it, will determine exactly what type of air treatment unit you should buy.

To help you select the right air treatment unit, we’ve provided more information about each type below.

Air filters: protecting tools from moisture and contamination

As you’ve probably guessed by the name, an air filter unit is designed to filter out solid particles (such as dirt, dust and other detritus) from compressed air systems. Air filter units will also separate liquids (such as water and oil).

Air filter units considerably reduce wear and tear on your air compression system and tools.

Air regulators: controlling pressure for your tools

An air regulator unit provides you with the ability to adjust the pressure or flow of air from your compressor.

This not only makes it easier to use compressed air for specific applications, but it also allows you to operate your pneumatic tools at the manufacturer’s recommended pressures, thus reducing wear and tear on your tools and prolonging their life.

It’s also possible to buy air regulator units which can be ‘locked’ once the pressure is set. These units are ideal for use with tools such as blowguns where the pressure must not exceed 2 bar.

Air lubricators: reducing tool wear in high-use systems

Finally, you have air lubricator units. These are units which are designed to release small, controlled amounts of oil into your pressurised air system. This helps to reduce friction and wear and tear on your air tools and equipment.

Air lubricator units are normally fitted close to the point of use and after an air filter unit (if you’re using one).

FRL units: when to use a combination unit

For most workshop setups, the simplest approach is an FRL unit, a single assembly that combines filter, regulator, and lubricator in one housing. You get all three functions from a single point in the system, which keeps installation clean and makes maintenance straightforward.

Where individual components make more sense: if you're running a mix of tools with different requirements on the same airline, you might use a filter and regulator at the main supply point, then add or omit a lubricator close to the specific tool that needs it. Spray guns are the common example, the compressor feeds a general system with lubrication, but the spray gun gets its air from a separate unlubricated branch.

The Hosemaster stocks FRL combination units, as well as individual filters, regulators, and lubricators for more complex setups.

How to choose the right air treatment unit for your system

At this point you might be wondering what type of air treatment unit is right for you. Do you just need a filter? Will a lubricator be necessary?

Below, we’ve provided the things you need to think about in order to buy the correct air treatment unit for your circumstances.

IMPORTANT: Verify lubricator recommendations against The Hosemaster product documentation. Some tools specify oil-free operation regardless of category — always check the manufacturer's manual.

When to use an air lubricator

Air lubricators add a fine mist of oil to the air supply. This reduces friction and wear in pneumatic tools, particularly those with internal valves and vanes that need a thin film of lubrication to run efficiently. Impact wrenches, air ratchets, grinders, and similar tools all benefit from it.

But lubrication isn't appropriate for every application. Spray guns used for painting need oil-free air, even a small amount of lubricant contaminates the finish. Digital tyre inflators and many types of spray equipment are in the same category. If you're in any doubt, check the tool manufacturer's specification. It will state whether the tool requires or prohibits lubricated air.

Fitting a lubricator close to the tool (rather than at the compressor outlet) also makes it easier to run a mixed system: lubricated air to the workshop bench, unlubricated air to the spray booth.

Filtration level

Whether you need to use an air filter unit or not is very much determined by the types of tools you’re working with.

Many tools have defined filtration requirements. Many industrial tools such as impact wrenches require 10-micron filtration, whereas more sensitive tools require a more stringent 5-micron filtration.

Whilst you may just think it’s easier to buy a filter unit with the highest level of filtration, you should avoid this. Don’t buy a finer filter than necessary. For example, don’t use a 5-micron filter with an impact wrench which only requires 10-micron filtration. Using a filter that’s too fine will not only increase energy consumption, but will increase wear on the tool.

Environment

Where will you be using your compressed air system? If you’re going to be using it in an environment where it will be subject to knocks and scuffs, or varying temperatures, then you need to make sure you buy an air treatment unit that is able to withstand it.

Here at The Hosemaster we sell a range of air treatment units that have robust designs manufactured from high-quality materials.

Airflow and port size

It’s important that you select an air treatment unit that is of the right size to match the airflow coming from your compressor and that is required by your tool. Failure to do so can result in the flow rate being affected and impaired performance.

We would suggest that you always refer to the tool manufacturer’s recommendations and buy an air treatment unit that has an air flow capacity that is greater than that which is required by the tool.

Drain type

When browsing for air filter units you’ll find that many feature a manual or semi-automatic drain at the bottom of the filter bowl.

This feature is included so that you can release the accumulated particles and liquids from the filter. With a manual filter, you have to do this yourself by hand. With a semi-automatic filter, it will automatically drain when the system is depressurised (although it is also possible to manually operate these types of drains).

It is recommended that you use a filter with a semi-automatic drain if you’re going to be using your compressed air system on a regular basis throughout the day.

Frequently asked questions

What is an FRL unit?

FRL stands for filter, regulator, and lubricator. An FRL unit combines all three functions in a single inline housing that fits between your compressor outlet and the airline. The filter removes moisture and particulates, the regulator sets and maintains a consistent output pressure, and the lubricator adds a fine oil mist to protect pneumatic tool internals. For most workshop setups, an FRL unit is the simplest way to treat compressed air before it reaches tools.

Do I need a lubricator for a spray gun? 

No, and you should actively avoid one. Spray guns require oil-free air. Even a small amount of lubricant in the air supply will contaminate the finish and can ruin a job. If your system has a lubricator on the main airline, run the spray gun from a separate unlubricated branch, or use an FRL unit without the lubricator module for that connection.

What micron filter do I need for an impact wrench? 

10-micron filtration is the standard recommendation for impact wrenches and most general pneumatic tools. Finer filtration (5 micron) is used for spray painting, food processing, and applications where very clean air is required. Don't specify finer than you need — a 5-micron filter used on a tool that only needs 10-micron will increase pressure drop across the filter and consume more energy for no benefit.

Get your perfect air treatment unit at The Hosemaster

Here at The Hosemaster we stock a wide range of air treatment units including models that include filters, lubricators and regulators in one unit, as well as individual filters, regulators and more.

You’ll also find a range of supporting accessories for air treatment units such as filter elements, brackets and more.

Shop air treatment units at The Hosemaster now

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