If you work in the field long enough, you know nitrogen generators rarely fail all of a sudden. They just become less useful over time. Purity drops a little. Flow reduces a bit. Energy consumption creeps up. Nobody checks until multiple issues pile up. Below is a list sorted by actual service call frequency. No fluff.
Purity Below Setpoint
This is the most common complaint. An operator sees purity drop from 99.5% to 97% and thinks the unit is broken. Most of the time it's not.
Check two things first:
- Is the purity analyzer probe contaminated with moisture or experiencing zero drift? This gets overlooked often on site.
- Is inlet pressure stable between 0.65 and 0.8 MPa?
If both are fine, look at the carbon molecular sieve. Typical CMS life is 3 to 5 years. But if oil and water removal at the front end is poor, the sieve can fail within one year. Put your hand at the bottom exhaust port of the adsorption tower. If you feel moisture or smell oil, the pre-treatment system is not doing its job.
Fix order:
Calibrate the instrument → check the dryer and precision filters → test CMS adsorption capacity on site by comparing inlet and outlet concentration with a nitrogen purity meter → replace the sieve only as a last step.
Enough Flow But Pressure Won't Reach Point of Use
Users often say: "The flow meter looks fine, but at the tool side there's no pressure." This usually is not a generator problem. It's piping or valves.
Two easily missed points:
- Is the check valve at the generator outlet stuck? Pull it off and blow through it to find out.
- Did someone change the pressure regulator setting downstream of the buffer tank?
Real case: A food packaging line used nitrogen. The flow meter read normal, but sealing results were poor. The cause turned out to be condensed water in the line. The nitrogen picked up moisture and lost purge effectiveness. Drained the water. Problem solved.
Recommendation: Check the entire path from the generator outlet to the point of use. Don't stare only at the generator.
Sharp Noise or Air Leak During Valve Switching
PSA generators rely on frequent valve switching. Unusual noise usually comes from a ruptured diaphragm in a pneumatic valve or a blocked pilot valve exhaust port.
Quick field check:
Touch the valve body. If the noise comes with abnormal vibration - diaphragm rupture. If you only hear a hissing sound but the valve does not move - burned pilot coil or exhaust port clogged with dust.
Replacement note: Don't replace just the broken diaphragm. Replace all diaphragms in the same batch together. In dusty environments, add a dust cap over the pilot valve exhaust port.
Power Consumption Up More Than 15% Compared to Last Year
Plant owners care about energy. If the compressor loading time gets noticeably longer but gas output stays the same, internal resistance inside the generator has likely increased.
Two most likely causes:
- CMS powdering. Black dust blocks the silencer and piping. Open the silencer and check for black powder.
- Inlet filter long overdue for replacement. High pressure drop.
Field data reference: On a 50 Nm³/h generator, when inlet filter pressure drop rises from 0.02 MPa to 0.08 MPa, compressor power consumption goes up by about 12%. Replace the filter element and it comes back down.
Purity and Flow Jump Around Unsteadily
This intermittent problem is the most annoying. Normal during the day. Unstable at night. Or it jumps whenever another machine starts.
Root cause: Inlet pressure swings or intermittent demand from the user side. The generator's control valve cannot respond fast enough.
Direct and effective fix:
- Add a buffer tank upstream of the generator. Volume should be at least 20% of compressor displacement.
- If you cannot add a tank, change purity control from continuous modulation to deadband control. For example, trigger an alarm only when purity drops below 97%. Stop frequent valve adjustments.
Frequent False Alarms on the Touchscreen
Common on site: The generator runs fine, but the screen shows a "low purity" or "pressure fault" alarm every ten or fifteen minutes.
Most likely a sensor issue, not a real fault.
- Pressure sensor zero drift. Check the zero reading after a power cycle.
- Purity analyzer sample flow too low or sampling line partially blocked.
Good practice: Check sensors first, then parameters. Many people start by adjusting parameters. That only hides the real problem.
Daily Maintenance List - Tape This on the Wall
- Daily: Check that the dryer drain is working properly.
- Weekly: Check the pressure drop gauge on precision filters.
- Monthly: Record purity and gas output once. Watch the trend.
- Every six months: Disassemble and inspect one set of valve diaphragms.
- Every two years: Test CMS performance and decide whether partial replacement is needed.
80% of nitrogen generator problems come from three things: dirty air supply, aged diaphragms, and uncalibrated instruments. Control these three, and you cut unplanned downtime by at least half. When in doubt, Shenger Gas recommends checking air quality first before tearing into the generator. Don't do the reverse.
