【Mechanical Equipment Technology Edition】Daily Question 201709021: Screw Compressors

Reason one: Is it because the liquid refrigerant has entered the compressor? There are two things to do: first, check whether the opening degree of the expansion valve is too high; if necessary, it should be reduced ； Next, check whether there is an excess of refrigerant; if it exceeds the specified limit, the excess refrigerant should be removed. Reason two: Is it due to a lack of oil or overload? The compressor oil level should be checked; if there is a lack of oil, it should be replenished immediately (please use compressor oil of the same brand) ； And check the compressor load. Reason three: Are the intake and exhaust valves damaged? If the suction and exhaust valves are damaged, it will inevitably affect the operation of the chiller. If inspection reveals that the intake and exhaust valves are damaged, replace them with new ones promptly. Reason four: Could it be that the anchor screws used to fix the chiller during installation are loose? When installing a chiller, it must be fixed to the floor or foundation. If the unit operates for an extended period of time, loose foot screws can also cause excessive vibration; therefore, it is sufficient to tighten the foot screws or replace them. Reason 5: Are there damages to the two components inside the compressor or is the clearance incorrect? Is the shock absorber in the wrong position? After shutting down the chiller, check and adjust the valve plate clearance, replace damaged parts, and inspect and adjust the shock absorbers. If the damage is severe, please contact the chiller manufacturer promptly. Reason 6: Is it due to poor fixation of the connection pipes or auxiliary equipment? Chillers, auxiliary equipment, and equipment that requires cooling are all connected through pipes. If these pipes are not properly secured, vibrations will occur when the chiller is turned on. Therefore, it is necessary to fix the connection pipes and equipment properly; shock absorbers should be installed if needed.

This post was last edited by ya1ya on 2017-9-21 at 10:07. In screw-type chiller units, the compressor vibrates during cooling operation and generates considerable noise. The possible reasons for high noise levels in such units include the following: 1. Insufficient refrigerant in the cooling system. 2. This is because screw refrigeration systems do not have an oil pump; instead, the pressure difference between the suction and discharge sides is used to achieve this. 3. Therefore, a shortage of refrigerant in the cooling system can result in a decrease in the exhaust pressure of the screw compressor as well as a low liquid level of the refrigerant in the evaporator. When the pressure in the cooling system is too low and the liquid level of the refrigerant in the evaporator is too low, it becomes difficult for oil to return to the system. This results in dry friction between the rotors, causing abnormal vibrations in the screw compressor and generating unusual noises. 4. Abnormal low-pressure differential in the refrigeration system, excessively low exhaust pressure of the screw compressor, and low oil pressure in the screw compressor all lead to overheating of the shafts, increased friction, and the generation of abnormal noises. 5. Issues such as a dirty and clogged oil filter or a deterioration in the quality of the oil can lead to an increase in oil pressure. Faults in the solenoid valves in the main oil circuit can also cause abnormal noises and sounds. 6. The moving parts inside the compressor may suffer from poor lubrication or damage.

Sources of noise in screw refrigeration compressors: 1. Vibration and noise generated by the air conditioning machinery in the machine room – imbalance of the rotor and its components; impact noise caused by rotor engagement and fluctuations in rotor speed; vibration and noise resulting from misalignment between the motor and coupling in open-type screw refrigeration compressors; vibration and noise from the bearings. Vibrations and noise from the outside of the machine include those from the casing, support structure, and base. 　　2. Fluid-induced noise: includes airflow noise and oil flow noise. Airflow noise includes suction and exhaust noises, such as vortex noises generated when gas enters or exits the suction and exhaust chambers as well as the volume of the rotor tooth grooves, and jet noises resulting from backflow and expansion during exhaust; pulsation noises in the air flow ducts and vibration noises at elbows; as well as noises from the suction and exhaust check valves. Oil flow noise includes injection noise, oil flow pipeline noise, oil pump cavitation, etc. 　　3. Electrical noise: In open-type screw refrigeration compressors, the motor noise consists of ventilation noise, mechanical noise, and electromagnetic noise, among others. General ventilation noise is relatively high; among mechanical noises, the noise from rolling bearings is next in intensity, while the noise from sliding bearings is lower. Electromagnetic noise is a noise specific to electric motors; it belongs to mechanical noise and is caused by harmonic magnetic field force waves in the air gap between the stator and rotor. When the power supply voltage is unstable, electromagnetic vibrations and noise are most likely to occur. 　　4. Unit noise: includes the vibration and noise of the oil separator, evaporator, and cooling system. Vibration and noise reduction measures 　Based on domestic and international research on the noise and vibration characteristics of screw-type refrigeration compressors, there is very little research on identifying noise sources, as well as on the distribution and properties of noise and vibration. To date, no comprehensive research framework or development system has been established in China; generally, noise testing systems are used to identify the key sources of vibration and noise, followed by the implementation of measures to reduce vibration and noise. Some companies have adopted a series of simple and effective measures in response to the common mechanical failures caused by abnormal vibration and noise. 　　1. Reducing power-frequency vibration using on-site dynamic balancing method (1) Check shaft bending and gaps in various parts. (2) Replace the bearing. (3) Reinforce the foundation. (4) Adjust the compressor level. (5) Adjust the clearance at the compressor exhaust end. (6) The two screws are dynamically balanced, with a balance accuracy exceeding the design requirements. (7) Refine the screws: place the two screws on a rolling machine, apply red lead powder to them, check the meshing condition, and grind off the high points. (8) Remove slag and dirt from the population pipeline. (9) Reinforce the outlet pipeline. (l0) Ensure precise alignment every time it is disassembled and assembled. 　　2. Correct the coaxiality between the motor shaft and the compressor main shaft to reduce vibration. 3. Replace flexible couplings of different types to lower the overall noise level of the machine. 　　4. Tighten components, improve assembly clearance, reduce bearing vibration, and lower machine noise

It is caused by the liquid refrigerant entering the compressor. Lack of oil or overload. The intake and exhaust valves are damaged. The anchor screws that were used for fixing during installation have loosened. Two components inside the compressor are damaged or have improper clearance. Poor fixation of connection pipelines and auxiliary equipment

1. Equipment foundation issues 2. Deviation in the installation of anchor bolts 3. Lack of shock absorption measures on the equipment base

There is insufficient refrigerant in the cooling system, the high-pressure difference in the cooling system is abnormal, and the moving parts inside the compressor may suffer from poor lubrication or damage

A faulty oil filter and poor oil quality can lead to increased oil pressure; a malfunction in the solenoid valve of the main fuel circuit can cause abnormal noises and rattling sounds

The refrigeration compressor itself can generate significant noise due to reasons such as improper assembly or detached springs.

Answer: 1. Vibration and noise in mechanical aspects. 2. Fluid-induced noise ； Including airflow noise and oil flow noise. 3. Electrical noise. 4. Unit noise, including the vibration and noise of the oil separator, evaporator, and cooling system.