Answer: (1) Cause analysis. Oil spraying of a screw air compressor refers to the oil spraying out of the air compressor air inlet. It usually occurs when the compressor stops suddenly, such as when the air compressor motor loses power or is shut down manually. At this time, the air compressor stops suddenly and the discharge valve is not opened in time to discharge the remaining gas in the air compressor oil tank. If the air intake check valve is not closed in time, the air compressor air inlet will spray lubricating oil out.
(2) Preventive measures. The treatment method for oil spraying of a screw air compressor should first check whether the oil shut-off solenoid valve is faulty. If it is normal, further check whether the check valve on the main exhaust pipe can be closed in time or whether it is closed completely. If there is a fault, it should be eliminated. At present, twin-screw air compressors are generally no longer equipped with oil shut-off solenoid valves, so the main cause of oil spraying is the check valve. It is recommended to use stainless steel valves for the selection of check valves, because the compressed air contains moisture and the oxidation and rusting speed of ordinary cast iron valves is very fast, causing the check valve to rust and become stuck and not closed tightly.
Once the power is off, the solenoid valve acts, the air intake butterfly valve is closed, and the initial isolation is achieved. However, there are usually vents or gaps on the air intake butterfly valve, which cannot be completely isolated from the outside. The heavy hammer check valve senses the change in air pressure and closes urgently. This is the most effective and final measure to prevent oil spitting. At present, twin-screw air compressors are generally not equipped with oil cut-off valves. After shutdown, they are isolated by check valves. When the oil pressed to the main engine is depressurized to zero inside the machine, it flows back to the oil tank under the action of gravity. The heavy hammer check valve is the most effective way at present. However, some domestic manufacturers generally use piston-type intake valves (or lifting valves) to save costs. The spring-controlled piston plays the dual role of intake regulation and check. After a long time, piston wear is inevitable, and oil spitting will occur during shutdown. Even normal shutdown will also cause oil spitting during shutdown. Therefore, manufacturers of this type of intake valve generally require the piston to be replaced every 3000~5000 hours.
