Insufficient or Fluctuating Pressure? Troubleshooting from the Inlet Valve to the Minimum Pressure Valve

CHANUN Air Compressor

Don't rush to shut down when pressure is unstable — learn the troubleshooting steps and you can often fix it yourself.
Pressure insufficiency or large pressure fluctuations are among the most common faults in air compressors. Many people’s first reaction is to stop the machine and call for repairs, but most pressure problems can be found and solved by a systematic check. Here’s how to step through the diagnosis — from the inlet valve to the minimum pressure valve.

01 — Outside first, inside later: eliminate external causes
When pressure anomalies occur, first inspect the external compressed-air system — this often quickly locates the issue and avoids unnecessary disassembly. The first step is to check whether the compressed-air demand has suddenly increased. If a large pneumatic device or additional air points were added, the compressor may not be able to supply enough flow and system pressure will remain low. You can test by closing the compressor outlet valve: if pressure then stabilizes at the set value, the external demand exceeds the compressor’s rated capacity; if pressure still drops, a pipeline leak is likely.
Also check whether downstream equipment such as dryers or filters is blocked. Even if the compressor’s outlet pressure is normal, blockages in downstream treatment equipment can make the point-of-use appear to have low pressure. Inspect filter elements for dust or oil sludge and measure pressure in sections with a gauge to localize the blockage.

02 — Focus on the inlet valve: the compressor’s “throat”
The inlet valve controls how much air the compressor takes in — it’s the machine’s “throat.” Its condition directly affects pressure stability. Common problems are valve sticking or poor sealing, which show as the pressure failing to reach setpoint, pressure creeping down slowly after rising, or increased noise when the compressor loads. These symptoms are often caused by lack of maintenance: oil, dust or fouling can jam valve plates, or seals can age and leak.
There are two common control modes for inlet valves: on/off (the inlet opens or closes when tank pressure reaches a limit) and modulation (the inlet opening is adjusted proportionally as pressure changes). Problems in the control lines — e.g., excessive moisture or a faulty solenoid — can also keep the inlet valve from opening or closing properly. Troubleshooting requires inspecting the valve: check that the plates move freely and that seals are intact. Minor sticking can often be cleared with a dedicated cleaner; seriously worn parts should be replaced.

03 — Minimum pressure valve: the “goalkeeper” of pressure stability
Although small, the minimum pressure valve (MPV) is critical for maintaining system pressure — it acts like a goalkeeper. Its main functions are to establish internal unit pressure to drive lubricant circulation; reduce air velocity through the oil–air separator to ensure separation effectiveness; and prevent backflow of compressed air during shutdown. Its normal operating range is typically 0.4–0.45 MPa: below setpoint the valve stays closed, above setpoint it opens.
Common MPV faults include damage from particles propelled by high-pressure flow, liquid-induced water hammer, or oil carryover that makes the valve sticky. These failures directly cause large pressure fluctuations or inability to build pressure. To diagnose MPV issues, measure the pressure drop across it: if the inlet–outlet differential is significantly larger than the normal operating range (usually not exceeding 0.2 MPa), or if pressure falls rapidly after shutdown, cleaning or replacement of the MPV is likely required.

04 — Systematic troubleshooting: proceed step by step
When facing pressure instability, follow an ordered, systematic approach: outside-to-inside and simple-to-complex. Start with external checks — changes in demand, pipeline leaks, clogged downstream equipment — and record how the pressure fluctuates. Note whether fluctuations correlate with particular equipment starting or stopping; that helps narrow the cause.
Then inspect core components in sequence: inlet valve → pressure sensor → minimum pressure valve. Inlet valve faults typically show as inability to raise pressure; sensor faults cause control anomalies; MPV faults usually produce large fluctuations or inability to maintain pressure. Use multiple detection methods: listen for abnormal airflow sounds, observe pressure gauge behavior, and use professional instruments for key parameters. An “intelligent monitoring system” that displays real-time pressure curves can be especially helpful to quickly locate faults.

05 — Preventive maintenance: the key to reducing pressure fluctuations
Regular maintenance is essential. Check control lines daily to prevent moisture-related faults; clean or replace filters periodically; change lubricant on schedule to prevent oil degradation from affecting parts. Use quality spare parts: inlet valve seals made from oil-resistant, high-temperature materials (for example, wear-resistant nitrile rubber) can last up to 50% longer than ordinary rubber; minimum pressure valves should be OEM or high-quality replacements to ensure dimensional fit and material integrity.
Keep maintenance records. Record each fault’s symptoms, the troubleshooting steps taken, and the corrective measures — over time this database reveals recurring issues and enables more targeted preventive maintenance.
Pressure problems are common but, if you troubleshoot methodically, most are solvable. From external supply and piping to internal components, and from simple checks to professional diagnostics, narrowing the scope step by step will lead you to the root cause. Mastering this troubleshooting process is like adding an insurance policy for steady equipment operation.