Screw-type air compressors are designed with high-temperature protection functions. When the exhaust temperature exceeds 100°C, the temperature sensor activates the temperature switch, triggering an alarm and automatic shutdown, while the instrument panel displays an exhaust temperature reading above 100°C. The machine's built-in cooling mechanism involves injecting lubricating oil from the lower and both sides of the main body into the compression chamber, where it mixes with the intake air and is compressed before being discharged from the bottom of the main unit into the oil-gas tank. In addition to lubricating components such as screws, bearings, and gears, the oil also carries away significant amounts of heat. However, before the next oil injection cycle, the heat must be transferred and the oil must pass through the oil cooler for complete cooling. Therefore, overheating faults are often related to abnormalities in the lubrication and cooling systems.

Below is a detailed analysis:

1. Lubrication System and Oil Circuit Components  

Insufficient lubricating oil or malfunctioning oil circuit components can cause oil temperature to rise, leading to overheating faults.

① Oil Shortage  

Check the oil level in the oil-gas tank. After shutdown and pressure release, the static oil level should be slightly above the high oil level mark (H or MAX). During operation, the oil level must not fall below the low oil level mark (L or MIN). If the oil level is insufficient or unobservable, stop the machine immediately and refill.

② Insufficient Oil Supply  

First, inspect whether the oil filter or oil separator is clogged. The oil separator, made of multi-layer fiberglass with a filtration precision of 0.1μm, filters oil mist from compressed air to prevent oil loss. In dusty environments, the replacement cycle should be shortened. Both the oil filter and oil separator are equipped with differential pressure switches to detect blockages by measuring the pressure difference across the filter. If clogged, replace them promptly. Next, check if the oil flow regulator is functioning properly. If necessary, increase the oil injection volume slightly. Note that the oil injection volume is preset at the factory and should generally not be altered.

③ Malfunctioning Oil Stop Valve  

The oil stop valve is typically a two-position, two-way normally closed solenoid valve that opens during startup and closes during shutdown to prevent oil from continuing to flow into the compressor head and spraying out from the intake port. If this component fails, the main unit may overheat rapidly due to oil shortage, potentially causing severe damage to the screw assembly.

④ Faulty Thermal Control Valve  

The thermal control valve, installed in front of the oil cooler, maintains the exhaust temperature above the pressure dew point. Its working principle: during startup, when the oil temperature is low, the bypass opens while the main circuit closes, allowing oil to bypass the cooler and enter the compressor head directly. As the temperature rises above 67°C, the valve gradually closes, allowing oil to flow through both the cooler and the bypass. Above 70°C, the valve closes completely, forcing all oil to pass through the cooler before entering the head, maximizing cooling. If the thermal control valve malfunctions, oil may bypass the cooler, preventing temperature reduction and causing overheating. Common causes include:  

- Changes in the elasticity coefficient of the two thermal-sensitive springs on the valve core due to fatigue, preventing proper temperature-responsive action.  

- Wear or jamming of the valve body, preventing the valve core from closing properly.  

Repair or replace the valve as needed.

⑤ Incorrect Lubricant Specifications or Poor Quality  

Screw compressors have strict lubricant requirements. Substitutes should not be used arbitrarily; always follow the specifications in the equipment manual.

2. Cooling System  

Screw compressors use either water-cooling or air-cooling systems. Check the following:

① Oil Cooler Performance  

For water-cooled models, check the temperature difference between the inlet and outlet water pipes. The normal range is 5–8°C. A difference below 5°C may indicate scaling or blockage, reducing heat exchange efficiency and causing poor cooling. Remove and clean the heat exchanger if necessary.

② Cooling Water Temperature and Pressure

For water-cooled models, ensure the inlet water temperature does not exceed 35°C, water pressure is maintained between 0.15–0.3 MPa, and flow rate is at least 90% of the specified value. For air-cooled models, check that the ambient temperature does not exceed 28°C. If these conditions are not met, consider installing a cooling tower, improving ventilation, or expanding the equipment room space. Also, inspect the cooling fan for proper operation and repair or replace it if faulty.

3. Air Intake/Exhaust and Control Circuit Components  

Malfunctions in these components can disrupt compressor operation and cause overheating. Check the following:

① Air Filter Blockage

Inspect or replace the filter based on the differential pressure switch alarm signal.

② Excessive System Pressure

System pressure is typically preset at the factory. If adjustment is necessary, use the rated air production pressure marked on the equipment nameplate as the reference. Over-adjustment increases machine load, potentially leading to overheating.