The occurrence and prevention of compressor wet stroke

1introduction

　　Small refrigeration compressors are mostly used to compress and transport Freon refrigerant vapor. Because the refrigeration system composed of it is simple and the operation process is unattended, when the system design is not perfect and the debugging is not careful, it is easy to cause wet stroke. When the compressor has a wet stroke, the sound is often abnormal, the body or cylinder is frosted, the cylinder is pulled to hold the shaft, the suction and exhaust are short-circuited, and the cooling capacity is reduced.

　　The wet stroke is caused by many factors, not only related to the structure of the compressor and the design of the refrigeration system, but also related to the debugging and control methods of the system. This article focuses on analyzing the causes of several typical wet strokes, and proposes effective improvements.

2Causes of wet stroke

　　When the compressor sucks in wet steam, a wet stroke occurs. The reason for the wet stroke in a large refrigeration system is the excessive liquid supply of the evaporator or the too small diameter of the vapor-liquid separation equipment. Small systems are mostly caused by improper design, adjustment and control.

　　There are three types of small refrigeration compressors: open, semi-closed and fully closed. For the open type, the only type of air intake is the direct type; the semi-closed type has the same method as the open type, and there is also a form of suction from the motor side; and the fully enclosed type only has the type where the air directly enters the body Types of. Due to the difference in air intake methods, their moisture resistance stroke capabilities are also different. The semi-closed type and the fully closed type are often stronger in the form of air intake from the motor side. The ability to withstand wet stroke only means that this type of model is not easy to be damaged when wet stroke occurs, and does not mean that it is still within the normal working range, that is to say, the compressor is working abnormally at this time.

　　The problem of refrigeration system design is reflected in the selection of thermal expansion valve and the connection form of the return pipe; adjustment refers to the adjustment of the opening degree when the expansion valve is selected reasonably; the control problem related to the wet stroke is mainly the compressor Start-stop method.

3Prevention of improperly designed wet compression

　　The thermal expansion valve is an automatic adjustment component of the refrigerant flow in the refrigeration system. The selection should be determined according to the refrigeration capacity of the compressor. Like the compressor, the cooling capacity of the expansion valve is also related to the condensing temperature, but the law is different. The relationship between the evaporation temperature of the HC (E) 1/2HW (R22) thermal expansion valve and the cooling capacity is shown in Figure 1. It can be seen that the cooling capacity is related to the evaporation temperature and the pressure difference before and after the expansion valve. If the condensing temperature is fixed, the cooling capacity will decrease when the evaporation temperature drops. Obviously, the effect on the cooling capacity of the expansion valve is that the evaporation temperature is greater than the pressure difference before and after the valve. When the evaporation temperature is fixed, the cooling capacity of the expansion valve increases with the increase of the pressure difference before and after the expansion valve, that is to say, it increases with the increase of the condensation temperature. When both the evaporating temperature and the condensing temperature change, the cooling capacity may increase or decrease.

　　The expansion valve product catalog only gives the cooling capacity of the valve under standard or air-conditioning conditions. When selecting, you must convert the cooling capacity according to the actual operating conditions before selecting, otherwise the selected expansion valve is either too large or too biased. If it is small, if it is too large, the throttling adjustment will no longer be effective, and it will easily cause wet stroke.