How to size and set up an air service unit (FRL)

What does a service unit consist of?

A service unit combines three components in flow direction: filter, pressure regulator and an optional lubricator (FRL, filter-regulator-lubricator). The filter separates condensate and particles, the regulator holds the working pressure steady, and the lubricator adds a fine oil mist for lubricated tools.

Order matters: filter first, then regulate, lubricate last. That keeps oil out of the regulator and cleans the air before the pressure is set. Many units also carry a gauge and a shut-off valve for de-pressurising the line.

• Filter: cyclone separation plus filter element, standard grade 5 µm, fine down to 0.01 µm.
• Regulator: keeps the secondary pressure stable despite a fluctuating inlet.
• Lubricator: sight-drip dispenses oil in proportion to air flow.
• Condensate drain: manual, semi-automatic or fully automatic.

How do you size port and flow rate?

Size the service unit by the required flow rate and the acceptable pressure drop, not just by the pipe thread. Too small and the pressure collapses at full load; too large and the lubricator doses poorly. Rule of thumb: choose a unit rated at least 20‑30 % above the peak demand of all connected tools.

Watch the nominal pressure drop: a well-sized unit loses only about 0.2‑0.5 bar at rated flow. Add up peak demand, add a reserve, then pick the body size - the thread is only the connection size, not the sizing criterion.

How do you set working pressure and lubricator?

Always set the working pressure from low to high: unlock the regulator knob, drop the pressure, then slowly turn up to the target value while the tool runs. This avoids overshoot. A typical value is 6 bar for many hand tools, though the tool datasheet is often lower.

• Compressor usually supplies 8‑10 bar line pressure as the primary feed.
• Set the regulator to the tool requirement, often 6 bar.
• Check pressure with the tool running, not idle (flow pressure counts).
• Lock the adjustment knob by pushing or clicking it after setting.

Dose the lubricator at the sight screw: guide value is about 1 drop per 300‑600 litres of air throughput, or 1‑2 drops per minute in continuous operation. Too much oil clogs and contaminates, too little lets tools run dry. Use only the pneumatic oil approved by the manufacturer (usually ISO VG 32).

How do you maintain filter and oil mist?

Maintenance means above all: drain condensate and replace the filter element in time. The filter bowl collects water and oil; if the level rises above the mark, condensate can be dragged into the line. An automatic drain empties itself, a manual one must be opened regularly.

• A rising pressure drop across the unit points to a clogged filter element.
• Water in the tool: check the drain, add a fine filter or fit a dryer.
• Oil despite oil-free operation: clean the old oiled line or replace components.

Frequently asked questions