Common Faults Of Screw Compressors

Common Faults Of Screw Compressors

1. Abnormal Compression Ratio: Compression ratio is a familiar concept to those knowledgeable about compressor performance. The difference between screw compressors and piston compressors is that piston compressors only under-compress, while screw compressors experience over-compression.

**Screw Compressor Ratio Too High:** The system may deviate from its design value. The main symptoms include excessively high discharge temperature and pressure, and excessively low suction pressure and temperature.

**Screw Compressor Ratio Too Low:** This primarily affects the wet stroke. In fact, screw compressors are more susceptible to wet strokes. If a large amount of liquid returns to the compressor, it will dilute the lubricating oil, resulting in the same effect as excessively high discharge temperature.

2. Low Condenser Efficiency: Low condenser efficiency mainly affects the supply liquid temperature and whether liquid can form. Excessive condensation is also problematic. For example, if the ambient temperature is low and the condensation effect is too good, the liquid will enter the evaporator more efficiently, resulting in very low suction superheat and low expansion valve sensitivity, which can cause liquid slugging at startup.

3. Low or High Evaporator Efficiency: Low evaporator efficiency mainly affects the cooling of the object being cooled, while its effect on the compressor is related to the wet stroke. High efficiency can lead to excessive suction superheat, which in turn affects the compressor's discharge temperature. Wet stroke conditions can be determined using a pressure-enthalpy diagram or by subtracting the condensation temperature from the discharge temperature.

4. Oil circuit issues: These mainly concern oil quality, cleanliness, and return oil temperature. The primary functions of lubricating oil in a screw compressor refrigeration system are lubrication, cooling, and sealing. The return oil temperature significantly impacts the screw compressor's lifespan; a recommended operating temperature is generally 40-60℃, although some manufacturers specify 70℃ or 80℃. Excessively high oil temperatures can cause oil coking, disrupting the oil film formation. Oil temperature also affects the discharge temperature, thus influencing the compression ratio.

5. Oil boiling during startup or operation: This fault indicates liquid ingress into the compressor, or excessive refrigerant in the lubricating oil. Please adjust the throttling mechanism and check for overcharging of refrigerant.

6. Insufficient or Excessive Oil Level: Insufficient oil level: Consider whether the oil separator is faulty, the amount of oil added is insufficient, or there is difficulty in oil return from the evaporator. During maintenance, check if there is no liquid level in the receiver; consider a faulty throttling mechanism or improper installation. Excessive oil level: Consider a clogged oil filter, or refrigerant mixed into the oil.

7. Excessively High Discharge Temperature: High discharge temperature has many causes, mainly considering excessive refrigerant, excessively high suction temperature, poor heat dissipation, unstable operating conditions, etc.

8. Low or Fluctuating Suction Pressure: Low suction pressure: Main causes include refrigerant deficiency, throttling mechanism malfunction, excessively high condensing temperature, liquid slugging, etc.