An FRL is used in preparing compressed air for use in your plant air system or for air tools and other applications in the home workshop. Essentially, an FRL will be useful anywhere you need to use compressed air.

There is no shortage of information on this site about the water problems air compressors create while compressing air. See the section under Water on the site map page.The FRL is designed to reduce or eliminate some of these water problems.

The FRL Acronym

The term FRL is an acronym for these three components that are used in compressed air treatment; the Filter, the Regulator and the Lubricator.

FRL - In That Order Please!

If you are using a complete FRL assembly to prepare your compressed air for use, do make sure that the order in which the filter, the regulator and the lubricator are installed in that order. The filter first, then the regulator, and then the lubricator if one is needed for the compressed air application.

The compressed air filter is installed first to remove particulates and free water before any dirty wet air gets to the regulator. Crud from the compressor air stream can quickly gum up a regulator, so putting the filter first keeps the air flowing to the air regulator as clean as possible.

The air regulator is installed next. Clean and relatively dry air can now be adjusted to the ideal air pressure that will flow downstream to the air tool or other air-using applications.

The filtered and now pressure-regulated compressed air will then flow through the lubricator and pick up the necessary lubricant for the tool or actuator. that is, if the lubricator is necessary. Quite often air using components are factory lubed, making the need for adding additional lubrication unecessary.

Do not install the lubricator first! If do, as air flows from the lubricator into the filter, most of the oil coming out of lubricator would be stripped from the air by the filter.

The regulator works best when regulating clean air, so installing it first would make no sense. If you were to install the regulator after the lubricator, you'd simply fill the flow path in the regulator with oil, in time, rendering it useless.

Just remember FRL is the name and that is the order in which these air treatment components are installed.

compressed air FRL

The picture shows a somewhat typical FRL. To the left is the filter, the regulator is in the middle, and the lubricator is to the right.

Female NPT ports are typically found on the inlet and outlet for the each of the three components to enable connecting to the air line and to each other.

Some FRL sets - like this one - come pre-assembled with proprietary connections between the F & R & L. Typically you will use a union to install the FRL set on the air line to enable removal of the FRL when maintenance becomes necesary.

Note The Arrows on the FRL

Note the arrow on the filter and lubricator caps. The arrow shows the route for the air flow. None of the components in the FRL will work properly if the air flows in the wrong direction.

The filter in the image has an automatic float type drain inside the bowl, though this is not visible from the picture. I know as I disassembled this particular unit after I took the photo. A bowl drain is an important part of the filter bowl, and one with an auto drain means that no maintenance person has to be concerned about regularly draining the bowl manually.

There is a sight glass on the side of both the filter and lubricator. The purpose is to show the liquid level inside the metal bowl on both the filter and lubricator, as the metal is opaque and cannot be seen through to detect the water level inside the bowl.

If the compressed air filter was a manual drain type, something I don't recommend, the sight glass will indicate the level of fluid inside the bowl. The maintenance operator can see if the bowl needs draining. I do not recommend a manual drain on filters as they quite often get forgotten, the bowl overfills, and now, instead of pulling free water out of the air stream, the filter becomes a source of water to downstream air components.

The FRL Lubricator

The lubricator has a sight glass on the bowl as well, and this allows the maintenance operator to monitor the level of lubricant in the bowl, without having to remove the bowl to check.

High speed air using equipment, equipment that often needs lubricating, can take advantage of auto-fill lubricators. An expensive option, but one that may become necessary as manually filling lubricators on a large piece of high-speed air-driven equipment may not be practical.

On top of the lubricator is another sight glass. The adjusting screw is used to modify the lubricant feed into the air stream. An operator can see that the lubricant is dripping into the air stream, and also see the results of flow adjustment by the turning of the adjustment screw.

When it comes to using a lubricator, less is more! Do not become one of the many who think that more lubricant dripping into the air stream is always better than a moderate drip of oil.

Once you start lubricating a compressed air using device, the lubricant you add will ultimately wash out any factory lubricant, and it is then necessary to keep lubricating that device for life.

While lubricant rates are predicated on the device being air-driven and the cycle speed of that device, a drop every 2-3 minutes should be adequate for all but most trying applications.

Regulator Orientation

The regulator can be installed in this modular type FRL as it shows in the picture, or it can be inverted so that the adjusting knob is at the top. The preference depends on the application.

The regulator can also be ordered as a locking unit, to help prevent unauthorized critical pressure settings in an air circuit.

Precision Regulators

Precision regulators, offering tighter pressure-setting accuracy and pressure level tolerance, are an available option, if the application requires it. Regulator manufacturers commonly offer general purpose and, higher priced, precision regulators if the application requires a greater pressure accuracy.

Regulators are available with a variety of pressure ranges to suit the specific application. Often the narrower the regulated pressure range the more accurate the downstream air pressure is.

FRL + Gauges

The pressure gauge shown in the photo above is of a general purpose design. They are cheap to build, yet reasonably effective in displaying the pressure of the regulator setting.

Other options for gauges include liquid filled, stainless steel bodies, a variety of pressure ranges, the gauge face size, among other options. Almost regardless of the application for regulating air a gauge can be found for the purpose.

Just remember. It's FRL people!