An FRL unit — filter, regulator and lubricator — is the air preparation set that sits between your compressor and the tools or machinery it feeds. Compressed air straight from the receiver is dirty, wet and at an uncontrolled pressure; feeding it directly into valves and actuators shortens their life and makes them unreliable. An FRL conditions the air so equipment receives clean air at the right pressure. This guide explains what each part does, why the order matters, and when the lubricator can be left out.
The Filter — Cleaning the Air
The filter is the first stage. It removes solid particles, pipe scale and condensed water from the air stream, protecting everything downstream. Air passes through a filter element (commonly 40 or 5 micron) and a swirl action drops water into a bowl, which is drained manually or automatically. For paint spraying, food or instrumentation you may add a second coalescing filter to remove fine oil mist and sub-micron particles. A blocked filter is a common cause of pressure drop, so check and drain the bowl regularly — our air preparation & condensate management range covers filters, dryers and drains.
The Regulator — Setting the Pressure
The regulator sets and holds a stable downstream pressure regardless of fluctuations in supply. Compressors typically run at 8–10 bar, but most tools and cylinders want less — running everything at full line pressure wastes energy and wears components. Set the regulator to the lowest pressure that does the job reliably; every bar you drop cuts air consumption and cost. A gauge shows the set pressure, and the regulator maintains it as flow demand changes.
The Lubricator — Adding Oil When Needed
The lubricator adds a fine, metered mist of oil into the air to lubricate the moving parts of air tools and some older valves and cylinders. It sits last in the unit so the oil is not stripped out by the filter. The feed rate is adjustable — a few drops per minute is usually plenty; over-oiling fouls silencers and contaminates the work. Because air that has been lubricated must stay lubricated for the life of the equipment, only fit a lubricator where the downstream kit actually needs it.
Why the Order Matters
The correct sequence is filter, then regulator, then lubricator — F, R, L, in the direction of flow. Filter first so the regulator and everything downstream see clean air; lubricator last so the oil is not caught by the filter. Getting the order wrong is a classic mistake, as is undersizing the unit: an FRL that is too small for the flow causes a large pressure drop under load, so the tool starves exactly when it is working hardest. Size the FRL to the port and flow rate of the equipment, not just the pipe thread, and mount it where the bowls are easy to see and drain.
When You Don’t Need a Lubricator
Much modern pneumatic equipment is designed to run on clean, dry, non-lubricated air. Most current solenoid valves, cylinders and air-prep components are pre-lubricated for life and can be damaged, or have their seals washed out, by added oil. For these, an FR unit — filter and regulator, no lubricator — is correct, and once you introduce oil you generally have to keep supplying it, so do not add a lubricator “just in case”. Check the equipment datasheet: if it specifies non-lube air, leave the lubricator out. If you are upgrading a compressor or air system, our Avelair compressors and regulator & lubricator assemblies are a good place to start, or get in touch for help specifying.
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