FRL festo

The Filter-Regulator-Lubricator, or FRL, is the starting point for any pneumatic machine or application. The name Filter-Regulator-Lubricator or FRL is often used, but this is actually outdated, as the supply unit is now much more than just a block to filter and regulate air.

Less attention is usually paid to it, but it is still very important. Below you will find an overview of the main components, their functions and applications. The illustrations are from the Festo MS series, with which we have a very comprehensive range that allows for an infinite number of possibilities.

Thanks to our partners, Elneo offers a wide range of FRLs and related services. Standard FRLs are available from stock and can be delivered within 24 hours.

Our experts are at your side to guide you in the selection of the ideal material and accessories for an optimal solution. Finally, we offer pneumatic diagrams and CAD files to design offices.

Robin Vanlook Robin Vanlook Sales Engineer
Need some advice on which FRL is right for you?

Our specialists are here to help you make this choice.

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Functional diagrams of an FRL

An ordinary valve is often used. It works in 2/2: 2 positions - 2 outputs (valve open - valve closed).

In itself, this is not a problem, but... all the air in the device remains in the device. With closed circuits, the energy of the compressed air is always present in the pipes/cylinders/valves.

FRL 2/2

For closed circuits, we recommend using a 3/2 valve: 2 positions - 3 outlets. This also allows all the air in the unit to be released when the compressed air supply to the machine is cut off.

FRL 3/2

The "filter" part of the FRL

The next step is the filter, or in most cases the filter and regulator.

The attached example is the MS6-LFR.

This combined element is the most used part of the FRL and forms the basis for everything that comes after. There are many options, so there is an item for every application. The most important ones are:

  • Pressure range: up to 2, 4, 7 or 12 bar.

Choose the maximum pressure value required by your machine, but more. The higher the value, the less precise the control knob will be. In addition, the pressure value on the manometer becomes less clear the higher the pressure.

  • Filter fineness

A standard 40µ filter element stops most water, dust and oil particles and is suitable for standard applications. If you have small cylinders or valve islands in your installation, you should use the 5µ filter elements instead. These stop even more due to the smaller pores, but with a lower flow rate.

  • Condensate treatment

If your filter is working well, a large part of the air contamination will have condensed against the wall of the pot due to the shape of the pot. These water and oil particles will collect at the bottom of the pot. In the case of automatic emptying, a float floats and evacuates the contamination using the air in the filter when the float reaches a certain level. Where there is a risk of greater contamination, such as in older galvanised steel air systems or where there is no optimal filtering at the compressor, the particles may be too large and block the float. In this case, a manual draining of the filter regulator is required.

  • Other

Such as the choice of a pressure gauge in BAR or PSI or an integrated pressure sensor with an M8 plug, etc.


An extra filter?

Sometimes 5µ is not enough, when operating requirements call for even cleaner air. In this case, it is possible to install an additional filter with a 1µ or 0.01µ filter element.

But beware of over-filtration, because each filter, each filter cartridge that the air passes through has an effect on the flow rate and a possible pressure drop, so it is advisable to size the installation properly.

The example on the left is the MS6-LFM.


The "lubricator" part of the FRL

At that time, it was common practice for moving parts to be lubricated with oil for proper operation. Today, almost all cylinders and other moving parts operate without oil, as the piston rod is lubricated for life during the production process.

Oil sprays are therefore much less common, except in applications where water or soap cleans parts with rotating properties, such as air motors or drilling/screwing tools. Our advice is to use a sprayer only when the application specifically calls for it, because once you start lubricating, there is no turning back.

The example on the right is the MS6-LOE.


Some frequently used products

In many cases, these basic items are sufficient to properly connect your device. However, there are some special items that are also often used.

The additional regulator: MS6-LRB

A machine often has a supply unit for a complete device with different functions. When all the components do not have the same pressure requirement, you can place this regulator between the two. It has a secondary output that gives a lower pressure than the previous regulator.

It is usually used to control several diaphragm pumps, or when a specific large cylinder needs 7 bar, but the other 20 cylinders can operate perfectly well at 4 bar. This saves a large amount of compressed air and money.


The membrane dryer: MS6-LDM1

The 0.1µ (or 0.01µ) fine filter removes water particles from the air, but this dryer will then dry the air, which is necessary in some applications. Please note that it consumes air when running.


3/2-way electric shut-off valve: MS6-EE

At the start of our FRL we place a manual valve, preferably a 3/2-way valve or "cut-off valve".  In an electrical version, we have this module, which switches the position of the valve when an emergency stop is pressed, for example, and which not only switches off the machine, but also depressurises it.


Quick-drain pressure relief valves: MS6-DE

Machines with many moving parts that suddenly stop must be reset. The cylinders are depressurised by the MS6-EE and are now in random positions. The danger is that when the compressed air is turned on, these cylinders are suddenly pressurised and make unexpected movements, which can lead to damage.

To ensure that this happens in a controlled manner, there is a pressure build-up valve.

Air is only admitted gradually, which slows down the pressure build-up. For example, when the pressure in the whole machine has reached 2 bar and everything has moved slowly back to its starting position, it switches on and gives the machine the required flow.


The safety combination: MS6-SV

This is a combination of a 3/2-way fast vent valve and a soft start. As the soft start is usually used in combination, this article is more interesting than the 2 separate articles.

This module is also available in a "safe" version (recognisable by the yellow strip). It can be connected to the PLC and ensures a safe connection of the compressed air to your unit.


This presentation is only a selection of the possibilities offered by FRL for a correct, safe and durable operation of your appliances. You can always contact your contact person to make an appointment with Elneo to analyse your installation and advise you.

FRL pneumatique

Robin Vanlook Robin Vanlook Sales Engineer
Need some advice on which FRL is right for you?

Our specialists are here to help you make this choice.

Free and fast quotation

+32 (0)476 20 69 34 Request a free and fast quote

Elneo is able to provide you with all of these pneumatic FRLs and more, thanks to recognised partners who are focused on quality and innovation. Our key partner for this product range is FESTO.

festo offical dealer

FRL's are part of our wide range of products available on our e-shop or in shop, deliverable in 24h or 48h.

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