With summer approaching, air compressors are prone to overheating. This article summarizes the possible causes of this problem.
1. Insufficient oil in the air compressor system. Check the oil level in the oil-gas separator. After shutdown and depressurization, the lubricating oil level should be slightly higher than the high oil level mark H (or MAX) when the lubricating oil is at rest. During operation, the oil level should not be lower than the low oil level mark L (or MIX). If insufficient oil is found or the oil level cannot be observed, stop the machine immediately and add oil.
2. Oil stop valve. The oil stop valve is generally a two-position, normally closed solenoid valve. It opens during startup and closes during shutdown to prevent oil from the oil-gas separator from continuing to spray into the compressor head and out of the air inlet when the machine stops. If this component does not open under load, the compressor will overheat rapidly due to lack of oil, which can seriously damage the screw assembly.
3.Oil filter problem.
A: A clogged oil filter and a blocked bypass valve will prevent compressor oil from reaching the compressor head, causing the compressor to overheat rapidly due to lack of oil.
B: A clogged oil filter reduces flow. One possibility is that the compressor doesn't completely remove heat, causing the temperature to rise slowly and eventually become high. Another possibility is that the compressor overheats after unloading. When the compressor is loaded, the internal oil pressure is high, allowing oil to pass through. However, after unloading, the oil pressure is low, making it difficult for oil to pass through the oil filter, resulting in insufficient flow and overheating.
4.Malfunction of the thermostat valve. The thermostat valve is installed before the oil cooler, and its function is to maintain the compressor head exhaust temperature above the pressure dew point. Its working principle is as follows: When the machine is first started, due to the low oil temperature, the thermal control valvethermostat valve branch opens, the main circuit closes, and the lubricating oil is sprayed directly into the machine head without passing through the cooler. When the temperature rises above 40℃, the thermostat valve gradually closes, and the oil flows through both the cooler and the branch circuit. When the temperature rises above 80℃, the valve closes completely, and all the lubricating oil then enters the machine head through the cooler to maximize cooling. If the thermostat valve malfunctions, the lubricating oil may enter the machine head directly without passing through the cooler, preventing the oil temperature from dropping and causing overheating. The main reasons for its failure are: firstly, the elastic coefficient of the two thermally sensitive springs on the valve core changes due to fatigue, preventing them from operating normally with temperature changes; secondly, valve body wear, causing the valve core to jam or not operate properly, preventing normal closure. Repair or replacement can be performed as needed.
5.The engine oil has exceeded its service life and has deteriorated.
6.Reduced oil fluidity and decreased heat exchange performance lead to incomplete heat dissipation from the air compressor head, causing overheating.
7.Check the oil cooler's operation. For water-cooled models, check the temperature difference between the inlet and outlet water pipes. Normally, this should be 5-8°C. A temperature below 5°C may indicate scaling or blockage, affecting the cooler's heat exchange efficiency and causing poor heat dissipation. In this case, the heat exchanger should be removed and cleaned.
8.Check if the cooling water inlet temperature is too high, and whether the water pressure and flow rate are normal. For air-cooled models, check if the ambient temperature is too high. The cooling water inlet temperature should generally not exceed 35°C, the water pressure should be between 0.3-0.5 MPa, and the flow rate should not be less than 90% of the specified flow rate. The ambient temperature should not exceed 40°C. If these requirements are not met, solutions include installing a cooling tower, improving indoor ventilation, and increasing the machine room space. Also check the cooling fan's operation; repair or replace it if faulty.
9.For air-cooled units, primarily check if the temperature difference between the inlet and outlet oil is around 10 degrees Celsius. If it's less than this, check if the radiator fins are clogged. If clogged, use clean air to remove dust from the radiator surface and check for corrosion on the radiator fins. If corrosion is severe, it's necessary to consider replacing the entire radiator assembly. Check for clogged internal pipes; if so, use a circulating pump to circulate a certain amount of acidic cleaning solution. Pay close attention to the solution concentration and circulation time to avoid radiator perforation due to corrosion.
10. Issues with the exhaust ducts installed by customers of air-cooled models. These include: insufficient airflow area in the exhaust duct; excessively long exhaust ducts; too many bends in the exhaust duct; many long exhaust ducts with bends lacking an exhaust fan; and exhaust fan flow rates lower than the original cooling fan supplied with the air compressor.
11. Inaccurate temperature sensor readings. If the temperature sensor is completely disconnected, the equipment will alarm and stop, displaying a sensor malfunction message. If the malfunction is intermittent, it's much more difficult to detect and troubleshoot, so substitution is a better approach.
12. Compressor Head Issues. Generally, the compressor head bearings should be replaced every 20,000-24,000 hours. The compressor's clearance and balance are determined by the bearings. Increased bearing wear causes direct friction in the compressor head, increasing heat and leading to high compressor temperatures. In severe cases, the compressor may seize up and become unusable.
13. Incorrect Lubricating Oil Specifications or Poor Quality. Screw compressors generally have strict requirements for lubricating oil and cannot be arbitrarily substituted. The specifications in the equipment's instruction manual should be followed.
14. Clogged Air Filter. A clogged air filter can cause excessive load on the air compressor, leading to prolonged overload and high temperatures. Check or replace the filter based on the differential pressure switch alarm signal. Generally, the primary problem caused by a clogged air filter is reduced air output; high compressor temperature is a secondary symptom.
15. Excessive System Pressure. System pressure is generally set at the factory. If adjustment is necessary, the rated gas production pressure indicated on the equipment nameplate should be used as the upper limit. If adjusted too high, the increased machine load will inevitably lead to overheating and overcurrent overload. Similar to the previous reason, high compressor temperature is a secondary symptom; the main manifestation is increased compressor motor current, causing compressor protection shutdown. 16. Oil-gas separator blockage. Oil-gas separator blockage can cause excessive internal pressure, which can lead to many problems, including high temperature. Similar to the previous two reasons, oil-gas separator blockage primarily manifests as high internal pressure.
The above are some possible causes of high temperature in screw air compressors, for reference only.
