Expansion valve is one of the four components of the refrigeration system, is an important device to regulate and control refrigerant flow and pressure into the evaporator, is also the high and low pressure side of the "dividing line". Its regulation is not only related to the normal operation of the whole refrigeration system, but also an important indicator to measure the technical level of operators.
The adjustment of the expansion valve must be carefully and patiently carried out. The adjustment of the pressure must go through the evaporator and the warehouse temperature to generate heat exchange boiling (evaporation), and then through the pipeline into the compressor suction chamber to reflect on the pressure gauge, which requires a time process. Every time the expansion valve is adjusted, it usually takes 15-30 minutes to stabilize the adjusting pressure of the expansion valve on the suction pressure gauge.
The suction pressure of compressor is an important reference parameter of expansion valve. The opening degree of the expansion valve is small, the flow rate through the refrigerant is small, the pressure is low; The opening of the expansion valve, refrigerant through the flow rate, pressure is high. According to the thermal 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, as the flow into the evaporator decreases and the pressure decreases, the evaporation speed slows down, the refrigerating 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 are too high. The flow and pressure into the evaporator are increased. Due to the excess liquid evaporation, the damp gas (or even the liquid) is sucked into the compressor, causing the wet stroke (liquid shock) of the compressor, which makes the compressor cannot work normally, causing a series of bad working conditions and even damage to the compressor.
Therefore, 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 adjusting the expansion valve, the expansion valve should be installed as far as possible on the horizontal pipeline away from the entrance of the cold storage. If the export expansion valve body side and bottom is 45 ℃ oblique frost, entry side shouldn't be frosted, indicates that accurate appropriate adjustment.
Otherwise, it shall be deemed that there is ice blocking or dirty blocking in the inlet filter. Under normal circumstances, the expansion valve is very quiet when working, if the more obvious "silk" sound, that the system is insufficient refrigerant. The expansion valve should be replaced when air leakage occurs in the temperature sensing system and adjustment failure occurs.
When there is frost at the inlet of the expansion valve (also frost or cover), the temperature of the liquid into the tube is lower than at room temperature, condensation, even under the temperature of the compressor suction pressure is lower than the library corresponding to the pressure, temperature and exhaust machine high temperature, cooling temperature decrease slowly or not, to explain the expansion valve filter blockage, there are dirty or ice blocking phenomenon.
Dirty or ice blocking treatment: close the liquid supply Angle valve, open the compressor operation, when the suction pressure is stable at 0, stop the compressor operation, close the compressor exhaust valve, open the expansion valve inlet, take out the filter to clean dirty. Then install the expansion valve and apply the freezing oil. If the system is severely blocked by ice, it is recommended to replace the dry filter or filter.
Debugging process and method of expansion valve:
1. Stop: insert the probe of the digital thermometer into the insulation layer at the evaporator air return port (corresponding to the position of the temperature sensing package). Connect the pressure gauge to the tee of the compressor low pressure valve.
2. Power on: let the compressor run for more than 15 minutes and enter a stable operation state, so that the pressure indicator and temperature display reach a stable value.
3. Calculation of superheat: read out the temperature T1 of the digital thermometer and the temperature T2 of the pressure measured by the pressure gauge, and the superheat is the difference between the two readings t1-t2.
4. Adjustment: screw down the bonnet below the thermal expansion valve and turn the stem clockwise to reduce the opening degree of the pinhole of the valve body, that is, to reduce the liquid flow. Counterclockwise rotation of the valve stem pinhole open, that is, increase the flow of liquid.