Operation: Analysis of 20 Major Faults of Screw Compressors!

Screw refrigeration compressor is a positive displacement compressor, which compresses gas by means of volume change. The compressor utilizes two screws with helical grooves in the body that mesh and rotate, and cooperate with the inner wall of the body and the inner wall of the suction and discharge end seats to cause changes in the inter-tooth volume, thus completing the processes of gas suction, compression and discharge. Screw compressors are now widely used in large air conditioning systems. Although the failure rate is relatively low, once a failure occurs, it must be taken seriously. Now let's take a look at the fault analysis of screw compressors.

1. Operation of Screw Refrigeration Compressor
1.1 First Start-up and Shutdown
Before starting up, the coupling must be realigned. For the first start-up, the working conditions of all parts of the compressor and electrical components must be checked first. The inspection items are as follows:
1.1.1 Close the power switch and select the manual position for the selector switch.
1.1.2 Press the alarm button and the alarm bell will ring; press the mute button to cancel the alarm.
1.1.3 Press the electric heating button and the indicator light will turn on. After confirming that the electric heater is working, press the heating stop button and the heating indicator light will turn off.
1.1.4 Press the water pump start button, the water pump will start and the indicator light will turn on. Press the water pump stop button, the water pump will stop and the indicator light will turn off.
1.1.5 Press the oil pump start button, the oil pump indicator light will turn on, the oil pump will run and the rotation direction is correct. Adjust the oil pressure difference to 0.4 - 0.6MPa. Operate the four-way valve or press the load increase and decrease button to check whether the slide valve and energy indication device are working properly. Finally, the energy level is indicated at "0".
1.1.6 Check the set values of each automatic safety protection relay or program:
1.1.6.1 High discharge pressure protection: Discharge pressure ≤ 1.57MPa
1.1.6.2 High oil injection temperature protection: Oil injection temperature ≤ 65℃
1.1.6.3 Low oil pressure difference protection: Oil pressure difference ≥ 0.1MPa
1.1.6.4 High pressure difference protection before and after the fine filter: Pressure difference ≤ 0.1MPa
1.1.6.5 Low suction pressure protection: Set according to the actual working conditions
After checking the above items, the unit can be started up. The start-up steps are as follows:
1.1.6.6 The selector switch is in manual start-up mode.
1.1.6.7 Open the compressor discharge stop valve.
1.1.6.8 Unload the compressor to the "0" position, that is, the 10% load position.
1.1.6.9 Start the cooling water pump and the coolant pump to supply water to the condenser, oil cooler and evaporator.
1.1.6.10 Start the oil pump.
1.1.6.11 30 seconds after the oil pump is started, when the pressure difference between the oil pressure and the discharge pressure reaches 0.4 - 0.6MPa, press the compressor start button, the compressor will start and the bypass solenoid valve A will also open automatically. After the motor is running normally, valve A will close automatically.
1.1.6.12 Observe the suction pressure gauge, gradually open the suction stop valve and manually increase the load. Pay attention that the suction pressure should not be too low. After the compressor is in normal operation, adjust the oil pressure regulating valve to make the oil pressure difference 0.15 - 0.3MPa.
1.1.6.13 Check whether the pressure and temperature of all parts of the equipment, especially the temperature of the moving parts, are normal. If there is any abnormal situation, stop the machine for inspection.
1.1.6.14 The initial running time should not be too long. It can be stopped after about half an hour. The shutdown sequence is to unload, stop the main unit, close the suction stop valve, stop the oil pump and stop the water pump to complete the first start-up process. When pressing the main unit stop button, the bypass solenoid valve B will open automatically and close automatically after shutdown.
1.2 Normal Start-up and Shutdown
1.2.1 Normal start-up process:
1.2.1.1 Select manual start-up, which is the same as the first start-up process.
1.2.1.2 Select automatic start-up:
1.2.1.2.1 Open the compressor discharge stop valve and start the cooling water pump and the coolant pump.
1.2.1.2.2 Press the compressor start button. At this time, the oil pump will automatically start to run and the slide valve will automatically return to the "0" position. After the oil pressure difference is established, the main motor will automatically start after a delay of about 15 seconds and the bypass solenoid valve A will open automatically. After the motor is running normally, valve A will close automatically.
1.2.1.2.3 When the main motor starts to start, the suction stop valve should be opened slowly at the same time, otherwise the excessive vacuum will increase the vibration and noise of the machine.
1.2.1.2.4 The compressor will automatically load up to 100% and enter the normal working state. And the load position will be automatically adjusted according to the pressure set value or the coolant temperature set value.
1.2.2 Normal shutdown process:
1.2.2.1 Manual shutdown is the same as the shutdown process of the first start-up.
1.2.2.2 The selector switch is in the automatic position:
1.2.2.2.1 Press the compressor stop button, the slide valve will automatically return to the "0" position, the main motor will automatically stop, and the bypass solenoid valve B will open automatically. The oil pump will stop automatically after a delay and valve B will close automatically after shutdown.
1.2.2.2.2 Close the suction stop valve. If the unit is shut down for a long time, the discharge stop valve should also be closed.
1.2.2.2.3 Turn off the water pump power supply and the compressor power switch.
1.3 Precautions during Operation
1.3.1 During the operation of the compressor, pay attention to observe the suction and discharge pressure, suction and discharge temperature, oil temperature and oil pressure, and record them regularly. The instruments are required to be accurate.
1.3.2 If the compressor stops automatically due to the action of a certain safety protection during operation, the cause of the failure must be found out before the machine can be started. It is absolutely not allowed to start the machine again by changing their set values or masking the fault.
1.3.3 When the main unit stops due to a sudden power failure, since the bypass solenoid valve B cannot be opened, the compressor may reverse. At this time, the suction stop valve should be closed quickly to reduce the reverse rotation.
1.3.4 If the unit is shut down for a long time in the low temperature season, all the water in the system should be drained to avoid freezing and damaging the equipment.
1.3.5 If starting the unit in the low temperature season, first start the oil pump and turn the coupling according to the motor rotation direction to make the oil circulate in the compressor and be fully lubricated. This process must be carried out in the manual start-up mode; if it is a Freon refrigerant, turn on the oil heater to heat the lubricating oil before starting up, and the oil temperature should be guaranteed to be above 25℃.
1.3.6 If the unit is shut down for a long time, the oil pump should be turned on once every about 10 days to ensure that all parts of the compressor are lubricated. Each time, the oil pump can be turned on for 10 minutes. Start the compressor once every 2 to 3 months for 1 hour each time to ensure that the moving parts will not stick together.
1.3.7 Before each start-up, it is best to turn the compressor a few circles to check whether there is any jamming in the compressor and make the lubricating oil evenly distributed in all parts.
2. Analysis of 20 Major Faults of Screw Refrigeration Compressor
2.1 Excessive Starting Load or Inability to Start at All
2.1.1 Reasons
2.1.1.1 The discharge end pressure of the compressor is too high.
2.1.1.2 The slide valve is not stopped at the "0" position.
2.1.1.3 The body of the machine is filled with lubricating oil or liquid refrigerant1.1.4 The moving parts are severely.
2. worn or burned.
2.1.1.5 Insufficient voltage.
2.1.2 Solutions
2.1.2.1 Let the high-pressure gas flow to the low-pressure system through the bypass valve.
2.1.2.2 Adjust the slide valve to the "0" position.
2.1.2.3 Turn the machine by hand to discharge the accumulated liquid and oil.
2.1.2.4 Disassemble, inspect and repair or replace the parts.
2.1.2.5 Inspect the power grid.
2.2 Abnormal Vibration of the Unit
2.2.1 Reasons
2.2.1.1 The foundation bolts of the unit are not tightened.
2.2.1.2 The vibration of the pipeline causes the vibration of the unit to intensify.
2.2.1.3 The concentricity of the coupling is not good.
2.2.1.4 Excessive oil or liquid refrigerant is sucked in.
2.2.1.5 The slide valve cannot be positioned and vibrates there.
2.2.1.6 The vacuum degree in the suction chamber is too high.
2.2.2 Solutions
2.2.2.1 Tighten the foundation bolts.
2.2.2.2 Add support points or change the support points.
2.2.2.3 Realign.
2.2.2.4 Stop the machine and turn it by hand to discharge the liquid from the compressor.
2.2.2.5 Check the unloading mechanism.
2.2.2.6 Open the suction valve and check the suction filter.
2.3 The Compressor Stops Automatically after Running
2.3.1 Reasons
2.3.1.1 The automatic protection set value is not appropriate.
2.3.1.2 There is a fault in the control circuit.
2.3.1.3 The motor is overloaded.
2.3.2 Solutions
2.3.2.1 Check and adjust the set value appropriately.
2.3.2.2 Check the circuit and eliminate the fault.
2.3.2.3 Check the cause and eliminate it.
2.4 Insufficient Refrigeration Capacity of the Compressor
2.4.1 Reasons
2.4.1.1 The position of the slide valve is not appropriate or there are other faults.
2.4.1.2 The suction filter is blocked.
2.4.1.3 The machine is severely worn, resulting in an excessive gap.
2.4.1.4 The resistance loss of the suction pipeline is too large.
2.4.1.5 Leakage between the high-pressure and low-pressure systems.
2.4.1.6 Insufficient oil injection quantity, weakening the sealing ability.
2.4.1.7 The discharge pressure is much higher than the condensing pressure.
2.4.2 Solutions
2.4.2.1 Check the position of the indicator or angular displacement sensor and repair the slide valve.
2.4.2.2 Remove the suction filter screen and clean it.
2.4.2.3 Adjust or replace the parts.
2.4.2.4 Check the suction stop valve or check valve.
2.4.2.5 Check the bypass valve and the oil return valve.
2.4.2.6 Check the oil circuit system.
2.4.2.7 Check the exhaust pipeline and valves and remove the resistance in the exhaust system.
2.5 Abnormal Noise during Operation
2.5.1 Reasons
2.5.1.1 There are sundries in the rotor tooth grooves.
2.5.1.2 The thrust bearing is damaged.

2.5.1.3 The main bearing is worn, and the rotor rubs against the body.
2.5.1.4 The slide valve is skewed.
2.5.1.5 The joints of the moving parts are loose.
2.5.2 Solutions
2.5.2.1 Inspect the rotor and the suction filter.
2.5.2.2 Replace the thrust bearing.
2.5.2.3 Replace the main bearing.
2.5.2.4 Inspect the guide block and guide column of the slide valve.
2.5.2.5 Disassemble the machine for inspection and strengthen the anti-loosening measures.
2.6 Excessive Discharge Temperature
2.6.1 Reasons
2.6.1.1 The compression ratio is relatively large.
2.6.1.2 The oil temperature is too high.
2.6.1.3 Severe superheating of the suction gas, or leakage of the bypass valve.
2.6.1.4 Insufficient oil injection quantity.
2.6.1.5 There is abnormal friction inside the machine.
2.6.2 Solutions
2.6.2.1 Reduce the discharge pressure and decrease the load.
2.6.2.2 Clean the oil cooler, lower the water temperature or increase the water volume.
2.6.2.3 Increase the liquid supply quantity, strengthen the heat insulation of the suction gas, and check the bypass pipeline.
2.6.2.4 Check the oil pump and the oil supply pipeline.
2.6.2.5 Disassemble and inspect the machine.
2.7 Decrease in Discharge Temperature or Oil Temperature
2.7.1 Reasons
2.7.1.1 Wet vapor or liquid refrigerant is sucked in.
2.7.1.2 Continuous operation without load.
2.7.1.3 The discharge pressure is abnormally low.
2.7.2 Solutions
2.7.2.1 Decrease the liquid supply quantity and reduce the load.
2.7.2.2 Check the unloading mechanism.
2.7.2.3 Decrease the water supply quantity and the number of condensers in operation.
2.8 The Slide Valve Moves Too Fast
2.8.1 Reasons
2.8.1.1 The opening degree of the manual valve is too large.
2.8.1.2 The oil injection pressure is too high.
2.8.2 Solutions
2.8.2.1 Close the oil inlet stop valve slightly.
2.8.2.2 Adjust the oil injection pressure downwards.
2.9 The Slide Valve Does Not Move Flexibly or Does Not Move
2.9.1 Reasons
2.9.1.1 The solenoid valve does not move flexibly.
2.9.1.2 The oil pipeline is blocked.
2.9.1.3 The opening degree of the manual stop valve is too small or it is closed.
2.9.1.4 The oil piston is stuck or leaks oil.
2.9.1.5 The slide valve or the guide key is stuck.
2.9.2 Solutions
2.9.2.1 Inspect the solenoid valve.
2.9.2.2 Inspect and repair.
2.9.2.3 Open the stop valve wider.
2.9.2.4 Inspect the oil piston or replace the sealing ring.
2.9.2.5 Inspect and repair.
2.10 Excessive Temperature of the Compressor Body
2.10.1 Reasons
2.10.1.1 The compression ratio is too large.
2.10.1.2 Insufficient oil injection quantity.
2.10.1.3 Severe superheating of the suction gas, or leakage of the bypass valve.
2.

10.1.4 Abnormal friction of the moving parts.
2.10.2 Solutions: The same as those for excessive discharge temperature. The main reason is the abnormal friction of the moving parts. Inspect the compressor or replace the thrust bearing.
2.11 Leakage of the Compressor Shaft Seal
2.11.1 Reasons
2.11.1.1 Insufficient oil supply to the shaft seal causes damage to the sealing ring.
2.11.1.2 Impurities in the oil wear the sealing surface.
2.11.1.3 Poor assembly and insufficient spring elasticity.
2.11.1.4 Deformation or damage of the "O" ring.
2.11.1.5 Inadequate contact between the stationary and rotating rings.
2.11.1.6 Excessive liquid refrigerant in the oil.
2.11.2 Solutions
2.11.2.1 Adjust the oil pressure or check the oil circuit.
2.11.2.2 Check the fine oil filter.
2.11.2.3 Adjust.
2.11.2.4 Replace.
2.11.2.5 Remove and re-grind.
2.11.2.6 Stop the machine and heat the oil.
2.12 Too Low Oil Injection Pressure
2.12.1 Reasons
2.12.1.1 Insufficient oil quantity in the oil separator.
2.12.1.2 Excessive refrigerant content in the oil.
2.12.1.3 Too high oil temperature.
2.12.1.4 Wear of the oil pump or malfunction of the oil pressure regulating valve.
2.12.1.5 The coarse and fine oil filters are dirty and blocked.
2.12.1.6 Large amount of oil leakage inside the compressor.
2.12.2 Solutions
2.12.2.1 Add oil or return the oil.
2.12.2.2 Stop the machine and heat the oil.
2.12.2.3 Lower the oil temperature.
2.12.2.4 Inspect, repair or replace, or adjust the oil pressure regulation method.
2.12.2.5 Clean the filter element.
2.12.2.6 Inspect the rotor, slide valve and balance piston.
2.13 Poor Oil Return
2.13.1 Reasons
2.13.1.1 The filter screen of the secondary oil separator falls off.
2.13.1.2 The oil return valve or filter is blocked.
2.13.2 Solutions
2.13.2.1 Inspect and repair.
2.13.2.2 Clean.
2.14 Increased Oil Consumption of the Compressor
2.14.1 Reasons
2.14.1.1 Too high oil pressure or excessive oil injection quantity.
2.14.1.2 Liquid return in the compressor.
2.14.1.3 High discharge temperature, reducing the efficiency of the oil separator.
2.14.1.4 Reduced efficiency of the oil separation filter element.
2.14.1.5 The oil separation filter element falls off or loosens.
2.14.1.6 Too high oil level in the secondary oil separator.
2.14.1.7 The oil return pipeline is blocked.
2.14.2 Solutions
2.14.2.1 Adjust the oil pressure or inspect the compressor.
2.14.2.2 Close the throttle valves of the evaporator and economizer slightly.
2.14.2.3 Refer to the solutions for excessive discharge temperature.
2.14.2.4 Replace the filter element.
2.14.2.5 Tighten or replace the rubber ring.
2.

14.2.6 Drain or return the oil to lower the oil level.
2.14.2.7 Clean and dredge the oil circuit.
2.15 Rise of the Oil Level in the Oil Separator
2.15.1 Reasons
2.15.1.1 The oil in the system returns to the compressor.
2.15.1.2 Excessive refrigerant enters the oil.
2.15.1.3 There is condensed liquid in the vertical oil separator level gauge.
2.15.2 Solutions
2.15.2.1 Drain the oil.
2.15.2.2 Raise the oil temperature to accelerate evaporation.
2.15.2.3 Calculate the actual height.
2.16 Reverse Rotation during Shutdown
2.16.1 Reasons
2.16.1.1 The suction and discharge check valves do not close tightly.
2.16.1.2 The bypass pipeline for preventing reverse rotation fails.
2.16.2 Solutions
2.16.2.1 Inspect and remove the jamming.
2.16.2.2 Check the bypass pipeline and the solenoid valve.
2.17 Too High Suction Temperature
2.17.1 Reasons
2.17.1.1 Insufficient refrigerant in the system, increasing the degree of superheat.
2.17.1.2 Small opening degree of the liquid supply valve or blocked pipeline.
2.17.1.3 Leakage of the bypass valve.
2.17.1.4 Poor thermal insulation of the suction pipeline.
2.17.2 Solutions
2.17.2.1 Detect and repair the leakage, and charge the refrigerant.
2.17.2.2 Increase the liquid supply and check the pipeline.
2.17.2.3 Check solenoid valves A and B and the oil return valve.
2.17.2.4 Inspect, repair or replace the insulation layer.
2.18 Low Suction Temperature
2.18.1 Reasons
2.18.1.1 Excessive liquid supply quantity to the evaporator.
2.18.1.2 Reduced heat exchange effect of the evaporator.
2.18.2 Solutions
2.18.2.1 Adjust the throttle valve or thermal expansion valve.
2.18.2.2 Clean the evaporator or drain the oil.
2.19 Too Low Suction Pressure
2.19.1 Reasons
2.19.1.1 Too low evaporation temperature, large heat exchange temperature difference.
2.19.1.2 Insufficient refrigerant in the system.
2.19.1.3 Small opening degree of the liquid supply valve; excessive resistance in the return air pipeline.
2.19.1.4 Small opening degree or malfunction of the suction stop valve.
2.19.1.5 The suction filter is dirty and blocked or iced up.
2.19.2 Solutions
2.19.2.1 Inspect the evaporator, increase the coolant flow rate, and reduce the compressor load.
2.19.2.2 Detect and repair the leakage, and charge the refrigerant.
2.19.2.3 Increase the liquid supply and check the pipeline.
2.19.2.4 Open the suction valve wider or check the valve head.
2.19.2.5 Clean the filter screen and remove the moisture.
2.20 Too High Condensing Pressure
2.20.1 Reasons
2.20.1.1 High cooling water temperature or insufficient water (air) quantity.
2.20.1.2 For evaporative condensers, the air humidity is too high.
2.20.1.3 Scaling or oil contamination in the condenser.
2.20.1.4 Excessive condensed liquid in the condenser.
2.20.1.5 Excessive non-condensable gas.
2.20.2 Solutions
2.20.2.1 Lower the water temperature or increase the water (air) quantity.
2.

20.2.2 Increase the air volume.
2.20.2.3 Clean, remove the scale and drain the oil.
2.20.2.4 Discharge the excessive condensed liquid in time.
2.20.2.5 Discharge the air in time.