An air filter removes water, oil vapour, and particulate from the compressed air stream before it reaches tools, valves, or processes. Water and particulate cause corrosion and accelerated wear in pneumatic tools and cylinders. Most filters use a spin-bowl method to separate bulk water and a filter element for finer particulate. The bowl needs to be drained regularly to prevent collected water from re-entering the air line.

An FRL unit combines three air treatment functions in one assembly: Filter (F), Regulator (R), and Lubricator (L). It is fitted between the compressed air supply and the equipment or circuit it serves. FRL units are common in machine-building because they simplify installation and reduce the number of individual connection points. They are available in various BSP port sizes to match different flow requirements.

Pull the adjustment knob outward to unlock it, then rotate to raise or lower the downstream pressure, reading the built-in gauge. Once set, push the knob back in to lock. Set the pressure with air flowing, not static, to account for pressure drop in the circuit. Most regulators are non-relieving, they will not bleed off pressure if the downstream pressure rises above the set point after the air is shut off.

It depends on the tool. Pneumatic impact wrenches, ratchets, grinders, and air motors generally benefit from oil lubrication. Spray guns, blow guns, and some valves require dry, clean air and should not have oil injected upstream. Check the tool manufacturer's recommendation. On circuits serving a mix of oil-requiring and oil-sensitive equipment, fit the oiler only on the branches where it is needed.

Fit the filter regulator as close to the point of use as practical, after the main air supply run. This ensures the tool receives treated air at the correct pressure regardless of what the supply is doing. On multi-tool circuits, fit individual regulators at each branch if different tools need different working pressures. Always install with the arrow on the body pointing in the direction of airflow.

BSPP (parallel) threads have a uniform diameter and seal via a bonded seal or O-ring on the face of the fitting. BSPT (tapered) threads taper slightly and seal on the thread itself, usually with PTFE tape. The two are not interchangeable. Most air regulators and FRL units in UK pneumatic systems use BSPP ports, check the port type before ordering fittings or adaptor nipples.

The Hosemaster delivers air filters, regulators, and FRL units to all UK mainland addresses. Orders over £200 to England and Wales qualify for free delivery, with 1-2 day delivery available and same-day dispatch on most in-stock lines. For help specifying the right unit, call 01282 604002.