1. The outlet of the evaporator should be checked for superheat using a thermometer or by observing the suction pressure.
2. If the superheat degree of the expansion valve is too low (due to excessive liquid supply), the adjusting rod should be rotated clockwise half a turn or one turn (i.e. increasing the spring force and reducing the valve opening) to reduce the refrigerant flow rate; The number of turns of the adjusting rod thread should not be too many (rotating the adjusting rod thread once will change the degree of superheat by approximately 1-2 °).
3. Experience in adjusting expansion valves: Rotate the adjusting rod thread to change the valve opening, so that frost or condensation can form just outside the evaporator return pipe. For refrigeration devices with evaporation temperatures below 0 degrees, if frost is formed and touched by hand, there is a cold feeling that sticks to the hand, and the opening is appropriate at this time; For evaporation temperatures above 0 degrees, it can be judged based on the condensation situation.
4. The correct debugging of the expansion valve directly affects the cooling effect and energy saving of the cold storage. Slow cooling in cold storage is often due to improper adjustment of expansion valves. 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. The adjustment of the expansion valve is the most critical among them. The opening degree of the expansion valve is small, resulting in less refrigerant flow and lower pressure; The larger the opening degree of the expansion valve, the greater the flow rate of refrigerant passing through, and the higher the pressure.
Precautions for Debugging Expansion Valve
If the outlet pressure of the expansion valve is too low, the corresponding evaporation pressure and temperature will also be too low. However, due to the decrease in flow rate and pressure entering the evaporator, the evaporation rate slows down, the refrigeration capacity per unit volume (time) decreases, and the refrigeration efficiency decreases. On the contrary, if the outlet pressure of the expansion valve is too high, the corresponding evaporation pressure and temperature will also be too high. The flow and pressure entering the evaporator increase, and due to the excess evaporation of liquid, the excess moisture gas (or even liquid) is sucked into the compressor, causing the wet stroke (liquid hammer) of the compressor, which makes the compressor unable to work normally, resulting in a series of harsh working conditions and even damaging the compressor. Therefore, the opening degree of the expansion valve should be adjusted according to the current storage temperature, that is, adjusted under the pressure corresponding to the storage temperature.
The adjustment of the expansion valve must be carried out carefully and patiently. The pressure adjustment must go through the evaporator and the storage temperature to generate heat exchange boiling (evaporation), and then enter the compressor suction chamber through the pipeline to reflect on the pressure gauge, which requires a time process. It usually takes 10-15 minutes to stabilize the regulating pressure of the expansion valve on the suction pressure gauge after each adjustment of the expansion valve. The adjustment should not be done too quickly. The suction pressure of the compressor is the main parameter for adjusting the pressure of the expansion valve.
Usually, faults such as filter blockage and leakage of temperature sensing agents are prone to occur. Causing insensitive regulatory response, loss of control or inability to regulate. When frost appears at the inlet of the expansion valve (or the valve cover also frost), the temperature of the inlet pipe is lower than room temperature, and even condensation occurs; The suction pressure of the compressor is lower than the corresponding pressure at the storage temperature, and the operating and exhaust temperatures of the machine are high. If the cooling temperature drops slowly or cannot be lowered, it is often due to filter blockage of the expansion valve or blockage of dirt and ice.
Debugging techniques and precautions for expansion valves
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