From intake filter to point of use
Air, oil, separator, dryer, coalescer and ISO 8573-1 purity classes are selected as a system, not as a single element.
A system, not one element
The intake protects the air end, the oil filter protects lubrication, the separator recovers oil, the coalescer removes aerosol and the final stage delivers point-of-use purity. ISO 8573-1 specifies particles, water and oil separately; one element cannot guarantee the full combination.
Each element depends on the adjacent stages: a blocked intake increases energy use, a damaged separator raises oil carryover, and an incorrect line filter cannot deliver the purity required by the user.
Five protection points in a compressor station
- 01Intake air filter
Removes dust ahead of the air end: panel, cylindrical and conical elements. Check airflow, area, interface, initial and terminal ΔP.
- 02Lube-oil filter
Protects the bearings and the screw element from wear debris. Valve setting, thread, rating, oil viscosity and cold-start conditions must match.
- 03Air-oil separator
Depth and coalescing layers return oil to the circuit and keep carryover low. Internal or external design, flange, gasket, grounding and allowable ΔP must match.
- 04Dryer and line filters
Particulate and coalescing filters remove particles, liquid water and oil aerosol downstream of the compressor; the dryer removes moisture and condensate. Housing and element are sized by flow, pressure and operating ΔP.
- 05Point of use
The final stage delivers process purity. An activated-carbon stage reduces oil vapour and odour after an effective coalescer, but does not replace liquid-aerosol removal and needs scheduled replacement.
Purity is specified for three contaminant groups
Particle, water and total-oil classes are specified separately. One filter name cannot guarantee a class: the outcome depends on the compressor, cooler, separator, dryer, drains, pipework and sampling point.
- Typical chain
- Separator → prefilter → dryer → dust afterfilter
- Key control
- Dew point, ΔP and drain operation
What to send for an accurate selection
- Compressor: make, model, serial number, OEM references and nameplate photo
- Duty: flow, pressure, temperature, operating hours, lubricant and site conditions
- Element: dimensions, thread or flange, gasket, valves, flow direction and photo
- Requirement: required air class, allowable ΔP, dew point, oil level and the critical point of use
Frequently asked questions
Why did the pressure drop rise after replacement?
Check flow direction, actual area, rating, gasket, flow and the adjacent stages. Matching external dimensions alone does not prove hydraulic equivalence.
Why is the compressor carrying oil over?
Possible causes include a damaged or overloaded separator, incorrect oil level, blocked scavenging line, wrong lubricant, short cycling or excess flow. Diagnose the system rather than replacing one element blindly.
How often should line filters be changed?
At terminal ΔP, the maker interval, a failed air-quality verification or damage, whichever occurs first. The interval depends on actual loading and drain performance.
Which elements belong in screw-compressor maintenance?
Normally the intake filter, oil filter and air-oil separator, subject to model and interval. Downstream coalescing filters, the dryer and automatic drains are checked separately.
Chain elements in 3D
On this topic
Intake air, lubricating oil, air-oil separation and downstream compressed-air treatment, selected as one system for screw, reciprocating and centrifugal compressors.
Open →Equipment filtersHydraulic, oil, fuel and air filters inside hydraulic power units, compressors, diesel gensets, gearboxes and lubrication systems.
Open →TroubleshootingSymptom → cause → check → action: a matrix for high ΔP, dust leakage, short life, wet cake and unstable measurements.
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