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How to debug the thermal expansion valve? How to deal with ice blockage/dirty blockage?

2018-12-17 01:11

The expansion valve is one of the four major components of the refrigeration system. It regulates and controls the flow and pressure of the refrigerant.EvaporatorThe important device is also the "dividing line" of the high and low pressure side ". Its adjustment is not only related to the normal operation of the entire refrigeration system, but also an important symbol to measure the level of operator technology!

The adjustment of the expansion valve must be carried out carefully and patiently. The adjustment pressure must pass through the evaporator and the warehouse temperature to generate heat exchange boiling (evaporation) and then enter the compressor suction cavity through the pipeline to reflect on the pressure gauge. It takes a time process. Each time the expansion valve is mobilized, it generally 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 the expansion valve to adjust the pressure. If the opening degree of the expansion valve is small, the flow rate of the refrigerant is small, and the pressure is also low; if the opening degree of the expansion valve is large, the flow rate of the refrigerant is large, 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 also too low. However, due to the decrease of the flow rate into the evaporator and the decrease of the pressure, the evaporation speed is slowed down, the cooling capacity per unit volume (time) is decreased, and the cooling efficiency is reduced.

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 rate and pressure entering the evaporator are increased. Due to the excess evaporation of liquid, excessive moisture gas (or even liquid) is sucked in by the compressor, causing the wet stroke (liquid hammer) of the compressor, causing the compressor to fail to work normally, resulting in a series of Bad working conditions and even damage the compressor.




From this point of view, the correct adjustment of the expansion valve is particularly important for the operation of the system. In order to reduce the pressure and temperature loss after the expansion valve is adjusted, the expansion valve is installed as far as possible on the horizontal pipe at the entrance of the cold storage, and the temperature sensing bag should be wrapped in the central position of the side of the return pipe (low pressure pipe). If the outlet side and lower part of the expansion valve body are 45 ℃ oblique frost, the inlet side should not be frosted, indicating that the adjustment is accurate and appropriate.




Otherwise, it is considered that the inlet screen is blocked by ice or dirt. Under normal circumstances, the expansion valve is very quiet when it works. If it makes a more obvious "silk" sound, it means that the refrigerant in the system is insufficient. When the expansion valve has faults such as air leakage and adjustment failure of the temperature sensing system, it should be replaced.

When frosting occurs at the inlet of the expansion valve (or the valve cover is also frosted), the temperature of the liquid inlet pipe is lower than normal temperature, or even dew, the suction pressure of the compressor is lower than the corresponding pressure under the reservoir temperature, the machine operating temperature and The exhaust temperature is high, and the refrigeration temperature drops slowly or does not drop, which is sufficient to indicate that the filter screen of the expansion valve is blocked, and there is dirty blockage or ice blockage.




Dirty blockage or ice blockage treatment method: close the liquid supply angle valve, open the compressor operation, when the suction pressure is stable at 0, stop the compressor operation, close the exhaust valve of the compressor, disassemble the liquid inlet of the expansion valve, Take out the filter screen to clean the dirt. Then install the expansion valve, and it is recommended that the sodium mouth be coated with frozen oil. If the system is severely icy, it is recommended to replace the dry filter or filter.

Debugging process and method of expansion valve:

1. Shutdown: Insert the probe of the digital thermometer into the thermal insulation layer at the air return port of the evaporator (corresponding to the position of the temperature sensing bulb). Connect the pressure gauge to the tee of the compressor low pressure valve.

2. Turn on: Let the compressor run for more than 15 minutes and enter a stable operating state, so that the pressure indicator and temperature display reach a stable value.




3. Calculate the superheat: read out the temperature T2 corresponding to the temperature T1 of the digital thermometer and the pressure measured by the pressure gauge, and the superheat is T1-T2

4. Adjustment: When adjusting, first unscrew the bonnet under the thermal expansion valve, and turn the valve stem clockwise to reduce the opening degree of the pinhole of the valve body, which means that the liquid supply flow is reduced. Counterclockwise rotation of the valve stem will open the needle hole, that is, the liquid flow increased.