Compressor Oil in CNG — Stopping Oil Carryover Before Storage, Dispenser and Vehicle
Lubricated CNG compressors always carry some oil into the gas. Without an effective coalescing stage after the final cooler, the oil travels on as aerosol and droplets — into storage, priority panels, dispensers and vehicle tanks, where it causes sticking valves, leaking nozzles and customer complaints.
Recognise the Symptoms
- Oily film or droplets at dispenser nozzles, breakaway couplings or filling receptacles
- Complaints from fleet operators about oil in vehicle tank valves, regulators or injectors
- Sticking priority valves, check valves or solenoid valves in the station
- Oil collecting in storage vessels and low points and released in slugs
- The existing line filter shows almost no differential pressure — or the element is soaked with oil
Root Causes
No coalescing stage after the final cooler
separators remove bulk liquid but not fine oil aerosol
Filter installed upstream of the cooler
in hot gas more oil is present as vapour, which passes any mechanical filter and condenses further downstream
Element efficiency too low for oil aerosol
a particulate element or a coarse coalescer lets fine droplets through
Drain not emptied
coalesced oil fills the housing bowl and is re-entrained into the gas
Compressor wear
worn piston rings and valves increase oil carryover over time
Element not changed
a saturated or damaged element loses efficiency; change at 0.7 bar ΔP and at least yearly
Diagnostic Checklist
- 1Is there a coalescing filter downstream of the final cooler — and what efficiency is its element rated for?
- 2What is the gas temperature at the filter inlet?
- 3How often is the filter drain emptied, and how much oil is collected?
- 4Is a differential pressure gauge fitted, and when was the element last changed?
- 5Is the compressor lubricated, and has oil consumption increased recently?
- 6Is oil vapour also a problem (odour, residue after the filter)? Then an activated carbon stage may be needed
- 7What operating pressure, flow (Nm³/h) and connection size apply?
Find the right filter for this problem
Enter your operating data and let our tools point you to the right element and housing — or send us your details for a tailored recommendation.
Element Finder
RecommendedIdentify the right filter element for your medium and duty in under 60 seconds — recommended starting point.
Find your elementUse Housing Selector
Select the matching housing — material, pressure rating, connections and drain.
Select a housingRequest a Consultation
Prefer a person? Send your operating data and we will recommend the right configuration.
Send enquiryRelated Applications
Describe Your Situation — We Will Find the Right Solution
Every filtration problem has specific root causes that require specific solutions. Send us your operating conditions and we will provide a tailored recommendation.