Process applications
Liquid and gas filtration: why ratings are not interchangeable
Distinguish flow references, condensation, wetting state and validation methods before transferring a filter between duties.
On this page
Establish the flow reference
Gas volume changes with pressure and temperature. A standardized volumetric flow and the actual volume in a pipe are different quantities, and reference standards may differ. Liquid comparisons also require temperature and viscosity; an air curve cannot be used as a liquid curve.
- State gas composition, flow units and standard or actual conditions.
- Distinguish absolute inlet pressure from gauge pressure.
Identify what reaches the membrane
Condensate, oil mist and droplets can alter membrane behaviour in a gas line. Hydrophobic does not mean impervious to wetting by every liquid, particularly mixtures with lower surface tension. Trapped gas in a liquid path can reduce effective area or destabilize start-up.
- Review upstream condensate and oil sources, including cooldown after shutdown.
- Observe whether liquid flow and differential pressure stabilize after controlled venting.
Evaluate both venting directions
Filling and emptying a tank create opposite gas demands, while temperature changes can alter internal pressure. Size a vent from relevant peak scenarios, not average production. Pressure and vacuum protection belong to the system design; a filter is not a substitute for a safety relief device.
- List maximum filling, emptying and cooling scenarios.
- Confirm permitted flow directions and condensate management.
Match evidence to the duty
Aerosol challenges, liquid challenges, particle-efficiency measurements and integrity tests answer different questions. For microbial control, obtain evidence applicable to the selected configuration and conditions, including the relationship between its integrity method and validated retention. A pore rating alone does not establish that relationship.
- Keep gas particle data separate from liquid retention data.
- State the control target and feasible on-site testing method in the enquiry.
Common technical questions
Will a hydrophobic membrane remain dry in every gas line?
No. Condensation, droplets and fluid composition require system-level control.
Can a gas filter resume service immediately after a water rinse?
Permitted rinsing and recovery procedures depend on the specific product and validated process.
Related product approaches
Check materials, configuration and validation documents for the specific model.