PSA nitrogen generator not reaching purity
How PSA works in one paragraph
A PSA generator passes compressed air through towers filled with carbon molecular sieve (CMS). Oxygen molecules are adsorbed faster than nitrogen, so nitrogen flows out. Before the sieve saturates, the tower is depressurised to release the oxygen and the other tower takes over. Purity depends on clean dry air, correct pressure, correct cycle timing, and not drawing more flow than the design.
Check these in order
- Over-draw: if production flow is above design, purity falls immediately. Throttle the outlet and watch purity recover.
- Inlet pressure: CMS capacity falls with pressure; 7–8 bar is typical.
- Air quality: oil carry-over or liquid water permanently damages CMS. Check the dryer dew point and coalescing filters.
- Valve operation: listen to each cycle. A leaking or stuck valve causes one tower to under-perform.
- Analyser calibration with zero and span gas.
When the sieve is the problem
CMS can also dust if the beds are not compacted, producing a fine black powder downstream. Settled beds create channels that let air bypass the sieve. If purity stays low after all checks, plan for a bed top-up or replacement by the manufacturer.
This guidance is general. Always follow the equipment manufacturer's manual and your site safety procedures. See our engineering disclaimer.