In many industrial plants, pressure swing adsorption (PSA) nitrogen generators gradually lose purity, struggling to hit the 99% setpoint. If not addressed quickly, this directly impacts downstream process stability and product quality. Most purity issues don't require a full machine replacement-they stem from a few key areas. Below is a step-by-step troubleshooting guide based on real-world conditions.
Verify the accuracy of your measurement method
When you see "purity below 99%," don't start adjusting the machine first. Confirm whether your measuring instrument is reliable. Field devices like paramagnetic oxygen analyzers, zirconia analyzers, or electrochemical sensors can drift over time. Use a standard gas (e.g., 99.99% nitrogen) for a quick check. If the reading deviates by more than ±0.5%, calibrate the instrument before proceeding. Also, check the sampling point-if the tap is too close to the outlet line, or if there are leaks or dead volume in the line, air ingress can falsely lower the reading.
Check for failed or powdered carbon molecular sieve
The heart of a PSA nitrogen generator is the carbon molecular sieve (CMS). If nitrogen purity gradually drops and adjusting the gas output doesn't help, the CMS is likely the culprit. Common causes:
1. Inadequate upstream oil/water removal-oil mist and moisture enter the adsorber and coat the sieve micropores, reducing separation efficiency.
2. Natural powdering over time (typically 3–5 years), blocking silencers or equalization valves.
Quick field check: Shut down, vent the tower, and open the drain port to see if black powder comes out. Visible powder means the sieve has powdered and needs replacement.
Inspect valve seals and timing sequence
Worn seal rings or spool damage in pneumatic and solenoid valves can cause cross-talk between adsorbers or inadequate pressure equalization. This issue is easy to miss because the machine still runs-purity just slowly drifts down. Listen for crisp valve switching sounds, and apply soapy water around valve bodies and connections to spot bubbles. Also, if the PLC switching timing has been altered manually or corrupted (e.g., after a power outage), the adsorption cycle may be disrupted. Compare against factory parameters and recalibrate each step.
Check front-end compressed air quality
The nitrogen generator's feedstock is compressed air. If the air from the compressor has a high dew point (excess moisture) or excessive oil content, CMS life drops sharply. Common scenarios: degraded performance of the refrigerated or desiccant air dryer, or clogged/damaged precision filter elements. Measure the compressed air before it enters the generator: pressure dew point ≤ -40°C, residual oil ≤ 0.01 ppm. If these conditions aren't met, even new CMS will fail again. Also, note the inlet air temperature-above 40°C reduces the sieve's dynamic adsorption capacity.
Adjust gas output and buffer storage
Some sites push output higher than the rated flow to meet production targets. When flow exceeds design limits, gas residence time in the adsorber shortens, and purity drops. Try closing the outlet flow valve by 10–20% and watch if purity recovers. If it does, you've been overproducing. Best practice: run at 90–100% of nameplate rated flow, and ensure sufficient buffer tank volume downstream to smooth out demand spikes.
Look for micro-leaks in the piping
Small leaks in pipes, valves, or fittings between the generator outlet and point of use-especially in intermittent-use systems where the outlet sees atmospheric or negative pressure-can suck in ambient air. Use a leak detector or soapy water to check all connections. Threaded joints and push-to-connect fittings are the most common spots for age-related loosening.
Follow this order for fastest troubleshooting
When purity falls below 99%, the recommended sequence is:
1. Confirm analyzer accuracy →
2. Check CMS condition →
3. Inspect valves and timing →
4. Verify upstream air quality and output flow.
About 80% of problems are found in the first two steps. Routine compressed air maintenance, along with regular filter and valve seal replacements, prevents most purity fluctuations.
If you've tried all the above and still have issues, Shenger Gas Technology recommends a systematic diagnostic using a dew point meter and residual oil detector-rather than repeated trial runs. Often, one thorough test saves more money than swapping parts blindly.
