The expansion valve is one of the four major components of the refrigeration system. It is an important device for regulating and controlling the flow and pressure of the refrigerant entering the evaporator, and it is also the "boundary line" on the high and low pressure sides. Its adjustment is not only related to the normal operation of the entire refrigeration system, but also an important indicator to measure the level of operator skills.
The harm of improper adjustment of thermal expansion valve:
First of all, we must know that the opening degree of the thermal expansion valve is too small or too large to be inappropriate.
If the opening degree of the thermal expansion valve is too small, it will cause insufficient liquid supply, so that there is not enough Freon to evaporate in the evaporator. The refrigerant has evaporated in the way of flowing in the evaporator tube. Liquid refrigerant is available for evaporation, only steam is superheated.
At the same time, the outlet pressure of the expansion valve is too low, and the corresponding evaporation pressure and temperature are also too low. As a result, the evaporation rate slows down, the cooling capacity per unit volume (time) decreases, and the cooling efficiency decreases. Therefore, a considerable part of the evaporator fails to give full play to its performance, resulting in insufficient cooling capacity and reducing the cooling effect.
If the thermal expansion valve is opened too large, the flow rate of the refrigerant will be large, that is, the amount of liquid supplied by the thermal expansion valve to the evaporator is greater than the evaporator load, so that the liquid refrigerant will evaporate too much, which will cause part of the liquid refrigerant to be too late in the evaporator Evaporation, together with the gaseous refrigerant, is sucked into the compressor, causing the wet stroke (liquid hammer) of the compressor, making the compressor unable to work normally, causing a series of accidents such as severe working conditions and even damage to the compressor by the cylinder.
At the same time, the thermal expansion valve is opened too large, so that the corresponding evaporation pressure and temperature of the refrigerant entering the evaporator are also too high, the cooling capacity decreases, the compressor power consumption increases, and the power consumption increases.
It can be seen that if the thermal expansion valve is too large or too small, it is harmful to the operation of the refrigeration system. Usually, when the thermal expansion valve is normal, there is frost at the outlet and lower part of 45℃.
Second, judge the thermal expansion failure
We can judge whether the adjustment size is appropriate through the change of the frosting shape of the thermal expansion valve:
1. If the frosting shape does not change when it is enlarged, it may be blocked.
2. If the expansion valve body only has frost on the outlet side, it indicates that the flow rate is too large.
3. If the expansion valve body is completely frosted, it indicates that 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 free of frost, it indicates that there is no flow. If there is no flow, see if the refrigerant has leaked out or the shut-off valve in the pipeline has not been opened.
If there is no flow at all, you can see if the capillary of the expansion valve temperature probe is leaking, or the filter is completely blocked!
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 optimal operating point, not because of the improper refrigerant charge of the system, the blockage of the filter dryer and the expansion valve, the failure of the solenoid valve, It is caused by other reasons such as poor heat dissipation of the condensing fan, refrigeration power of the newly replaced compressor, and unequipped system. At the same time, the correctness of the sampling signal of the temperature sensor must be ensured. The installation position of the temperature sensor must be correct. It must not be installed directly under the pipe to prevent factors such as oil accumulation at the bottom of the pipe from affecting the correct temperature of the temperature sensor. In addition, if it is lost When the thermal expansion valve with adjustment function is replaced with a new expansion valve, the new product has generally been debugged and checked before leaving the factory, so it is not necessary to adjust the expansion valve and install it directly.
1, stop. Insert the probe of the digital thermometer into the insulation layer at the 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, power on. Let the compressor run for more than 15 minutes to enter a stable operation state, so that the pressure indicator and temperature display reach stable values.
3. Read the value. Read the temperature T1 of the digital thermometer and the temperature T2 corresponding to the pressure measured by the pressure gauge. The superheat is the difference between the two readings T1-T2. , The standard of overheating is 5~8℃.
4. Adjust. When adjusting, first unscrew the bonnet under the thermal expansion valve, and turn the valve stem clockwise to close the needle hole of the valve body, that is, the liquid supply flow is reduced (in short, the needle is turned down); otherwise, the needle The opening of the hole increases, that is, the flow of the liquid supply increases (in short, the reverse rotation is large). The method is the same as that of adjusting the water valve to control the size of the water flow. Finally, Lauf Refrigeration reminds you that the flow adjustment should be carried out during the normal operation of the refrigeration system, and it should be operated slowly and adjusted gradually.