Why filtration is a chain, not a filter
Compressed air carries three things that damage equipment: water, particulate and oil. No single element removes all three efficiently. A staged chain does the coarse work first so the fine stage is not blinded, which is why the Q, P and S sequence exists.
- Q - bulk separation. Cyclonic and coalescing separation of bulk water and larger particles.
- P - fine coalescence. Removes finer aerosol oil and particulate carried through the Q stage.
- S - final polish. The fine element that takes residual oil down to the class required by the process.
Element sizes
The QPS element series is offered in 015, 024, 035, 060 and 090 sizes, with CTAFH elements available in the same family. Match element size to the actual flow through the housing, not to the pipe diameter, and check the pressure drop at rated flow.
| Target | Typical arrangement |
|---|---|
| General workshop air | Receiver plus refrigerated dryer, single coalescing filter |
| Painting, powder coating | Refrigerated dryer plus Q and P stages |
| Instrument air, laser assist gas | Adsorption dryer plus Q, P and S stages |
The 0.001 mg/m3 threshold
Residual oil of 0.001 mg/m3 is the ISO 8573 Class 1 limit, and it is only reachable with a final coalescing stage, in practice behind a dryer that has already removed the water. A filter alone cannot deliver that figure on wet air, because carried-over condensate re-contaminates the element.
Maintenance reality
Differential pressure tells you when an element is loading up. Waiting for visible oil downstream means the element has already failed open. Change intervals should be driven by pressure drop and running hours, not by calendar alone, and the drain on each stage has to be working, or the element sits in water and bypasses.
Tell us your working pressure, required flow and site voltage, and we will match a configuration. Send an enquiry.