The expansion valve is one of the four components of the refrigeration system. It is an important device for regulating and controlling the refrigerant flow and pressure into the evaporator, and is also the “demarcation line” on the high and low pressure side. Its regulation is not only related to the normal operation of the entire refrigeration system, but also an important indicator to measure the level of operator technology.
The adjustment of the expansion valve must be carried out with patience. The adjustment pressure must be exchanged between the evaporator and the storeroom to generate heat (boiling) and then enter the compressor through the piping. The suction chamber is reflected on the pressure gauge and takes a time course. Every time the expansion valve is mobilized, it usually takes 15-30 minutes to stabilize the adjustment pressure of the expansion valve on the suction pressure gauge.
The suction pressure of the compressor is an important reference parameter for adjusting the pressure of the expansion valve. The opening degree of the expansion valve is small, the flow rate of the refrigerant passing through is small, and the pressure is also low; the opening degree of the expansion valve is large, the flow rate of the refrigerant passes through, and the pressure is also high. According to the thermodynamic properties of the refrigerant, the lower the pressure, the lower the corresponding temperature; the higher the pressure, the higher the corresponding temperature. According to this law, if the outlet pressure of the expansion valve is too low, the corresponding evaporation pressure and temperature are too low. However, due to the decrease in the flow rate into the evaporator, the decrease in pressure causes the evaporation rate to slow down, the unit volume (time) cooling capacity to decrease, and the cooling efficiency to decrease. On the contrary, if the outlet pressure of the expansion valve is too high, the corresponding evaporation pressure and temperature are also too high. The flow and pressure into the evaporator are increased. Due to excess liquid evaporation, the excessive moisture (or even liquid) is inhaled by the compressor, causing the compressor's wet stroke (liquid blow), making the compressor unable to work properly, resulting in a series of work Bad condition and even damage the compressor.
Correct adjustment of the expansion valve to the operation of the system is particularly important. In order to reduce the pressure and temperature loss after adjustment of the expansion valve, the expansion valve should be installed as far as possible on the horizontal pipe at the entrance to the cold storage. The temperature sensing bag should be wrapped in the central side of the return pipe (low pressure pipe). In the normal operation of the expansion valve, the frosting of the valve body is oblique, and the inlet side should not be frosted, otherwise it should be regarded as an ice block or dirty plugging of the inlet filter. Under normal circumstances, the expansion valve is very quiet when working, if the more pronounced "silk" sound, indicating that the refrigerant system is insufficient. The expansion valve should be replaced when there is a malfunction of the temperature sensing system, such as air leakage and regulation failure.
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