Because of the pressure and temperature loss of the pipeline (depending on the length of the pipeline and the insulation effect), the suction temperature is 5-10 ℃ higher than the evaporation temperature, the corresponding suction pressure should be 0.66 ~ 0.23MPa gauge pressure. Adjustment of the expansion valve must be carefully and patiently, adjusting the pressure must be through the evaporator and the warehouse temperature to produce heat exchange boiling (evaporation) and then through the pipeline into the compressor suction chamber is reflected in the pressure gauge, need a time process. Every mobilization of the expansion valve once, it generally takes 15-30 minutes to stabilize the expansion valve pressure adjustment in the suction pressure gauge. The suction pressure of the compressor is an important reference parameter for the adjustment pressure of the expansion valve. Expansion valve opening degree is small, the refrigerant through the flow is less, the pressure is also low; expansion valve opening degree is large, the refrigerant through the flow is more, the pressure is also high. According to the thermal properties of 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 is also too low. However, due to the reduction of flow into the evaporator, the pressure is reduced, resulting in slower evaporation, unit volume (time) cooling capacity down, refrigeration efficiency is reduced. On the contrary, if the expansion valve outlet pressure is too high, the corresponding evaporation pressure and temperature is also too high. Into the evaporator flow and pressure are increased, due to excess liquid evaporation, excess moisture gas (or even liquid) is inhaled by the compressor, causing the compressor wet stroke (liquid strike), so that the compressor can not work properly, resulting in a series of poor working conditions, and even damage to the compressor. From this point of view, the correct adjustment of the expansion valve is particularly important to the operation of the system.
In order to reduce the pressure and temperature loss after adjustment of the expansion valve, the expansion valve as far as possible installed in the cold storage maintenance from the entrance to the horizontal pipeline, temperature-sensitive package should be wrapped in the return pipe (low-pressure pipe) side of the central position. Expansion valve in normal operation, the valve body frost is oblique, the inlet side should not be frost, otherwise it should be regarded as the inlet screen there is an ice blockage or dirty blockage. Under normal circumstances, the expansion valve work is very quiet, if the more obvious "silk" sound, indicating that the system is not enough refrigerant. When the expansion valve temperature sensing system leakage, regulation failure and other faults should be replaced.