Ⅰ. High Discharge Temperature at Compressor Air‑end Outlet

Excessive temperature rise is a common fault during operation of screw air compressors. Long‑term high‑temperature operation will seriously reduce the compressor’s delivery capacity and service life, and may trigger high‑temperature shutdown. Causes:

1. Faulty temperature sensor. A defective temperature sensor causes the PLC to give a false overtemperature alarm and trigger shutdown.

2. Ambient‑temperature influence. The typical set‑point for screw‑compressor air‑end outlet temperature is around 110 °C; air‑end outlet temperature equals ambient temperature plus 60 °C. Poor ventilation in confined/pit environments is a frequent cause of overtemperature.

3. Faulty thermal control valve. During cold start‑up, the thermal valve bypasses oil around the cooler and injects oil directly into the air‑end to speed up oil‑temperature rise and prevent internal condensation. Under normal operation, it modulates the oil flow split between cooler and bypass circuit to control injection‑oil temperature. If the thermal valve is damaged or sluggish, large volumes of hot oil circulate directly back to the air‑end without cooling, resulting in high air‑end temperature.

4. Faulty oil filter. The oil filter removes dust and contaminants in the oil circuit. It may become blocked after service, restricting oil return and raising air‑end temperature (often occurring the instant the compressor is loaded).

5. Faulty oil‑injection valve. The oil‑injection valve is actuated reciprocally by receiver‑tank air pressure to deliver injection oil. A fault may restrict oil flow and raise oil temperature. Debris clogging the oil circuit or control‑air circuit can cause the oil‑injection valve to close and stop oil supply; insufficient oil supply impairs heat dissipation and leads to high air‑end temperature.

6. Insufficient lubricating‑oil volume, or dirty / blocked oil cooler, both resulting in overtemperature.

7. Faulty cooling fan, blocked air cooler, excessive exhaust resistance lead to poor heat dissipation and high temperature. Clean external dust and internal oil contamination on the cooler.

Ⅱ. Low Discharge Pressure

1. Actual air consumption exceeds unit output. Inspect connected equipment and piping network; repair any leakage points. If system demand consistently exceeds compressor output under normal operating conditions, install a larger‑capacity unit or add extra compressors.

2. Low unloading‑pressure set‑point. Set unloading pressure correctly to achieve full operating efficiency.

3. Dirty / blocked air‑filter element causes insufficient inlet air flow and low discharge pressure. Inspect the air filter and replace if required.

4. Faulty solenoid valve. Leakage from the main vent solenoid valve and cold‑start blow‑off solenoid valve in the discharge piping; replace valves.

5. Leaking control‑air hose. Replace control‑air hoses.

6. Sluggish intake valve failing to open fully. Perform overhaul and inspect the control system.

7. Blocked oil‑gas separator. Replace the oil‑gas separator element.

8. Leaking safety valve. Re‑calibrate or replace the safety valve.

9. Stuck‑open drain valve on air‑water separator causing leakage. Overhaul the drain valve.

10. Faulty blow‑off valve that cannot close on compressor loading. Overhaul or replace the blow‑off valve.

Ⅲ. Excessively High Discharge Pressure

1. Faulty intake valve. Overhaul or replace.

2. Improper loading / unloading pressure settings. Adjust loading‑unloading set‑points according to actual air demand.

3. Faulty pressure sensor. Replace the sensor.

4. Unloading‑valve malfunction: stuck or poorly‑seated unloading valve, or faulty solenoid valve. Overhaul unloading valve and solenoid valve; replace components if necessary.

Ⅳ. Frequent Loading‑Unloading Cycling

1. Too narrow differential pressure between loading and unloading set‑points on the pressure controller. Reset loading and unloading pressures.

2. Blocked or leaking pressure‑sampling tube leading to rapid pressure decay. Overhaul the sampling piping.

3. Unstable production‑site air consumption (fluctuating or intermittent demand). Install an additional air receiver downstream of the compressor unit.

4. Minimum‑pressure valve fails to close promptly or seal tightly during compressor unloading. Overhaul the minimum‑pressure valve and replace if needed.

5. Faulty load‑control solenoid valve. Inspect the solenoid valve; water‑oil‑air contamination may cause sluggish movement or burnt coil. Inspect and replace as required.

6. Defective pressure sensor for unit start‑stop control. Overhaul or replace.

Ⅴ. Compressor Remains Continuously Loaded (Will Not Unload)

1. Actual production air consumption exceeds compressor output, keeping the unit in permanent loaded operation.

2. Check for air leakage along connected piping network.

3. Verify whether loading‑unloading solenoid valves actuate properly or are damaged.

4. Check tight shut‑off of the compressor intake valve.

5. Inspect drain valve of air‑water separator for leakage.

6. Check safety valve and oil‑gas separator for internal leakage.

Ⅵ. Excessive Oil Consumption or Oil Carry‑over in Compressed‑Air Discharge

1. Over‑filling lubricating oil. Excessively high oil level allows airflow to entrain oil from the oil‑gas separator into compressed air, causing excessive oil content in outlet air. Maintain oil level between the red mark and yellow mark on sight glass.

2. Failed spring inside minimum‑pressure valve results in low opening pressure. High differential pressure across the oil‑gas separator raises flow velocity of oil‑gas mixture inside the tank. High‑speed gas strips condensed oil from the vessel wall and separator element, degrading oil‑gas separation performance.

3. Blocked or damaged oil‑gas separator element. Inspect, clean or replace.

4. Blocked oil‑return pipe of oil‑gas separator. Inspect and clean.

5. Leakage in air‑cooled circuit. Inspect, repair and seal leaks.

6. Oil service life expired or oil degraded. Flush the compressor unit and replace with qualified lubricant.

Ⅶ. Excessive Unit Noise

1. Compressor mechanical fault: damaged bearing or rotor failure inside air‑end. Shut down immediately and contact dealer or after‑sales service centre.

2. Poorly fitted enclosure panels or damaged sound‑absorbing cotton.

3. Loose components. Thoroughly inspect and tighten all connecting parts.