The compressor is a driven fluid machine that delivers gas and increases gas pressure. It is the heart of the refrigeration system and provides power for the refrigeration cycle, thereby realizing the refrigeration cycle of compression → condensation → expansion → evaporation (heat absorption). Common faults are as follows.
1. Abnormal suction temperature
The suction temperature of the compressor refers to the refrigerant temperature read from the thermometer in front of the compressor suction stop valve. In order to ensure the safe operation of the compressor and prevent liquid hammer, the suction temperature is required to be slightly higher than the evaporation temperature, that is, it should have a certain degree of superheat. The magnitude of the superheat can be achieved by adjusting the opening degree of the expansion valve.
Avoid suction temperatures that are too high or too low. If the suction temperature is too high, that is, the superheat is too large, it will cause the compressor exhaust temperature to rise. If the suction temperature is too low, it means that the refrigerant is not completely evaporated in the evaporator, which not only reduces the heat exchange efficiency of the evaporator, but also causes compressor liquid hammer due to the inhalation of wet steam. Under normal circumstances, the suction temperature should be 5~10℃ higher than the evaporation temperature
2. The suction temperature is too high
Under normal circumstances, the compressor cylinder head should be half cool and half hot. If the suction temperature is too high, the cylinder head will heat up. If the suction temperature is higher than normal, the exhaust temperature will also rise accordingly. The main reasons for the suction temperature being too high are: (1) The refrigerant charge in the system is insufficient. Even if the expansion valve is opened to the maximum, the liquid supply will not change. In this way, the refrigerant vapor will overheat in the evaporator and the suction temperature will rise. (2) The expansion valve is opened too small, resulting in insufficient circulation of the system refrigerant, less refrigerant entering the evaporator, high superheat, and high suction temperature. (3) The expansion valve port filter is blocked, the liquid supply in the evaporator is insufficient, the refrigerant liquid volume is reduced, and part of the evaporator is occupied by superheated steam, so the suction temperature rises. (4) Other reasons cause the suction temperature to be too high, such as poor insulation of the return air pipe or too long pipe, which can cause the suction temperature to be too high. 3. The suction temperature is too low. In theory, the compressor operates best when the steam in the compressor is saturated. In order to ensure the safe operation of the compressor and prevent wet stroke, a certain degree of superheat must be achieved. If the suction temperature of the compressor is too low, it is easy to produce a wet stroke and deteriorate the lubrication conditions, so this phenomenon should be avoided as much as possible. The reasons for the compressor suction temperature being too low are:
(1) The refrigerant is filled too much, occupying part of the volume in the condenser and increasing the condensing pressure, and the amount of liquid entering the evaporator increases accordingly. The liquid in the evaporator cannot be completely vaporized, so that the gas sucked into the compressor contains liquid droplets. In this way, the temperature of the return air pipe drops, but the evaporation temperature does not change because the pressure does not drop, and the superheat decreases. Even if the expansion valve is closed, there is no significant improvement.
(2) The expansion valve is opened too much. Because the temperature sensor is tied too loosely, the contact area with the return air pipe is small, or the temperature sensor is not wrapped with insulation material and the wrapping position is wrong, the temperature measured by the temperature sensor is inaccurate and close to the ambient temperature, which increases the opening degree of the expansion valve action and causes excessive liquid supply.
4. Abnormal exhaust temperature
The compressor exhaust temperature can be read from the thermometer on the exhaust pipe. It is related to the adiabatic index of the refrigerant, the compression ratio (condensing pressure/evaporating pressure) and the suction temperature. The higher the suction temperature, the greater the compression ratio, the higher the exhaust temperature, and vice versa. When the suction pressure remains unchanged and the exhaust pressure increases, the exhaust temperature rises; if the exhaust pressure remains unchanged and the suction pressure decreases, the exhaust temperature also rises. Both situations are caused by the increase in the compression ratio. Excessive condensation and exhaust temperatures are detrimental to the operation of the compressor and should be prevented. Excessive exhaust temperature will make the lubricating oil thinner or even carbonize and coke, thereby deteriorating the lubrication conditions of the compressor.
The exhaust temperature is proportional to the compression ratio (condensing pressure/evaporating pressure) and the suction temperature. If the suction superheat temperature is high and the compression ratio is large, the exhaust temperature will also be high. If the suction pressure and temperature remain unchanged, when the exhaust pressure increases, the exhaust temperature will also increase.
The main reasons for the increase in exhaust temperature are:
(1) The suction temperature is high, and the exhaust temperature of the refrigerant vapor after compression is also high.
(2) The condensation temperature increases, and the condensation pressure also increases, causing the exhaust temperature to increase.
(3) The exhaust valve plate is broken, the high-pressure steam is repeatedly compressed and the temperature rises, the cylinder and the cylinder head are hot, and the thermometer indication on the exhaust pipe also increases.
(4) In addition, for water-cooled machines, water shortage or insufficient water will increase the exhaust temperature. Abnormal condensation pressure and reduced exhaust pressure.
5. High exhaust pressure
The exhaust pressure is generally corresponding to the condensation temperature. Under normal circumstances, the exhaust pressure of the compressor is very close to the condensation pressure. When the condensation pressure increases, the compressor exhaust temperature also increases. The compression ratio of the compressor increases, the gas transmission coefficient decreases, and the refrigeration capacity of the compressor decreases. The power consumption increases. If the exhaust temperature is too high, the consumption of the compressor lubricating oil increases, the oil becomes thinner, and the lubrication is affected; when the exhaust temperature is close to the flash point of the compressor oil, part of the lubricating oil will be carbonized and accumulated at the suction and exhaust valve ports, affecting the sealing of the valve.
Reducing the temperature of the cooling medium can reduce the condensation temperature and the condensation pressure, but this is subject to environmental conditions and is difficult to select artificially. Increasing the flow rate of cooling medium can reduce the condensation temperature a little (this method is often used). However, the flow rate of cooling water or air cannot be increased unilaterally, because this will increase the power of the cooling water pump or fan and motor, and should be considered comprehensively. A high exhaust pressure will increase the compression work and reduce the air transmission coefficient, thereby reducing the refrigeration efficiency.
The main reasons for this failure are:
(1) The cooling water (or air) flow rate is small and the temperature is high;
(2) There is air in the system, which increases the condensation pressure;
(3) The refrigerant is filled too much, and the liquid occupies the effective condensation area;
(4) The condenser is in disrepair for a long time, and the heat transfer surface is seriously fouled, which can also cause the condensation pressure to increase. The presence of scale also has a great impact on the condensation pressure.
6. Exhaust pressure is too low
Common reasons for low exhaust pressure:
(1) The expansion valve is blocked by ice or dirt, and the filter is blocked, etc.;
(2) The refrigerant charge is insufficient;
(3) The expansion valve hole is blocked, and the liquid supply is reduced or even stopped.
7. Insufficient exhaust volume
Insufficient exhaust volume is mainly compared with the designed air volume of the compressor. Insufficient exhaust volume is one of the most common faults of the compressor. Its occurrence is mainly caused by the following reasons:
(1) The air intake filter is blocked by dirt or the compressor suction pipe is too long and the pipe diameter is too small, which increases the suction resistance, affects the suction volume and reduces the exhaust volume.
(2) The compressor speed is reduced, which reduces the exhaust volume.
(3) The cylinder, piston and piston ring are seriously worn, which affects the exhaust volume.
(4) The packing is not tightly sealed and leaks, which reduces the exhaust volume.
(5) The influence of the compressor suction and exhaust valve failure on the exhaust volume.
(6) The valve spring force and gas force are not well matched.
(7) The clamping force of the clamping valve is improper.
8. Abnormal sound
When some parts of the compressor fail, they will make abnormal sounds. For example, the crankshaft bolts, nuts, connecting rod bolts, and cross head bolts in the crankcase are loose, disengaged, or broken. The shaft diameter is severely worn, the gap increases, and the clearance between the cross head pin and the bushing is too large or severely worn. These can all cause knocking sounds in the crankcase. The exhaust valve plate is broken, the valve spring is soft or damaged, and the load regulator is improperly adjusted. These can all cause knocking sounds in the valve cavity. This should be followed to find the fault and analyze its cause so as to take measures.
