How to judge the failure of thermal expansion valve? How to adjust the thermal expansion valve?

The thermal expansion valve is one of the four components of the refrigeration system, which is an important device to regulate and control the refrigerant flow and pressure into the evaporator, and also the "dividing line" between the high and low pressure sides Its regulation is not only related to the normal operation of the whole refrigeration system, but also an important indicator of operator technology I hazards of improper adjustment of thermal expansion valve: first of all, we need to know that the opening degree of thermal expansion valve is too small or too large If the opening degree of the thermal expansion valve is too small, the liquid supply will be insufficient, so that there is not enough freon to evaporate in the evaporator, and the refrigerant has evaporated in the way of flowing in the evaporation pipe After that, there is no liquid refrigerant to evaporate in the evaporator pipe, only the steam is overheated At the same time, the outlet pressure of expansion valve is too low, and the corresponding evaporation pressure and temperature are too low As a result, the evaporation rate slows down, the refrigerating capacity per unit volume (time) decreases, and the refrigerating efficiency decreases Therefore, a large number of evaporators fail to give full play to their efficiency, resulting in insufficient cooling capacity and reducing the cooling effect If the thermal expansion valve is opened too much, the flow of refrigerant will be more, that is to say, the liquid supply from the thermal expansion valve to the evaporator is greater than the load of the evaporator, so that the liquid refrigerant evaporates too much, which will cause part of the liquid refrigerant to evaporate in the evaporator too late When the same gaseous refrigerant is inhaled into the compressor, it will cause the wet stroke (liquid strike) of the compressor, which will make the compressor abnormal Work, resulting in a series of bad working conditions, even cylinder damage compressor accident At the same time, the opening of the thermal expansion valve is too large, so that the corresponding evaporation pressure and temperature of the refrigerant entering the evaporator are too high, the cooling capacity is reduced, the power consumption of the compressor is increased, and the power consumption is increased It can be seen that too large or too small thermal expansion valve is not conducive to the operation of the refrigeration system Normally, there is 45 ℃ frost at the outlet and lower part of the thermal expansion valve when it is normal, as shown in the figure below Normally, there is frost at the outlet and the lower part at 45 ℃ 2 To judge the thermal expansion fault, we can judge whether the adjustment size is appropriate through the frost shape change of the thermal expansion valve: 1 If the frost shape does not change when the size is increased, it may be blocked Expansion valve cleaning 2 If only the outlet side of the expansion valve is frosted, the flow is too large 3 If all the expansion valve bodies are frosted, the flow is too small 4 If only the inlet side of the expansion valve body is frosted, it indicates that the filter screen at the inlet of the valve body is blocked and should be cleaned 5 if the expansion valve body is completely frost free, there is no flow No flow to see if the refrigerant leakage is complete or the stop valve in the pipeline is not open If there is no flow at all, you can see if the capillary of the expansion valve temperature probe leaks, or the filter screen is completely blocked! The sound of "silk" from capillary leakage of temperature probe indicates that the refrigerant is insufficient 3 Adjustment method of thermal expansion valve Before adjusting the thermal expansion valve, it must be confirmed that the abnormal refrigeration is caused by the deviation of the thermal expansion valve from the Zui's good working point, not by other reasons such as improper refrigerant filling volume of the system, blockage of the filter screen of the drying filter and expansion valve, failure of the solenoid valve, poor cooling of the condensing fan, cooling power of the new compressor and system not equipped At the same time, it must be ensured that the sampling signal of the temperature sensing package is correct, and the installation position of the Gan temperature sensing package must be correct, and it can not be installed directly under the pipeline, so as to prevent factors such as oil accumulation at the bottom of the pipe from affecting the temperature sensing package In addition, if the thermal expansion valve without regulating function is replaced with a new expansion valve, generally the new product has been debugged and calibrated before delivery, so it is unnecessary to adjust the expansion valve and open it for direct installation and use 1 Shut down Insert the probe of the digital thermometer into the insulation layer at the air return port of the evaporator (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 Allow the compressor to run for more than 15 minutes and enter the stable operation state, so that the pressure indication and temperature display reach the stable value 3 Read the value Read out the temperature T2 corresponding to the pressure measured by the digital thermometer T1 and the pressure gauge The superheat is the difference T1-T2 between the two readings The superheat standard is 5-8 ℃ 4 Adjustment When adjusting, first screw off the valve cap under the thermal expansion valve, turn the valve rod clockwise to make the pinhole opening of the valve body turn down, that is, the flow of liquid supply is reduced (briefly speaking, the flow of liquid supply is reduced by unscrewing clockwise); otherwise, the pinhole opening is large, that is, the flow of liquid supply is increased (briefly speaking, the flow of liquid supply is increased by unscrewing reversely) It is the same as regulating water valve to control water flow After Zui, the flow regulation needs to be carried out in the normal operation of the refrigeration system, and it needs to be operated slowly and adjusted gradually.