Matters needing attention in installation and debugging of expansion valve in small cold storage

The capacity of small cold storage is generally less than 100 tons. R22 is used as the refrigerant for compressors, semi-enclosed compressors are used for low-temperature storage, and fully enclosed compressors are used for high-temperature storage. Evaporator of cold storage can adopt exhaust pipe or air cooler.

First, the small cold storage thermal expansion valve installation experience summary

1. Check whether the temperature sensing bulb is in good condition before installation;

2. The installation position of the expansion valve must be close to the evaporator, and the valve body should be installed vertically;

3. During installation, attention should be paid to keep the liquid in the bulb always in the bulb, so the bulb should be installed lower than the valve body;

4. The temperature sensing bulb should be installed on the horizontal return pipe at the outlet of the evaporator as far as possible, and should generally be more than 1.5M away from the compressor suction port;

5. The temperature sensing bulb cannot be installed on the return pipe with accumulated liquid;

6. If there is a gas-liquid exchanger at the outlet of the evaporator, the temperature sensor is generally packaged at the outlet of the evaporator, that is, before the heat exchanger;

7. The temperature sensing bulb is usually placed on the evaporator air return pipe, and tightly bound against the pipe wall, and the contact points should be cleaned;

8. When the diameter of the air return pipe is less than 25MM, the temperature sensor can be tied at the top of the air return pipe. When the diameter is greater than 25MM, it can be tied at the lower side of the air return pipe 45 to prevent the oil accumulation at the bottom of the pipe from affecting the temperature sensing effect of the temperature sensing package;

Second, debugging technology of thermal expansion valve in small cold storage

1, evaporator outlet should use thermometer to measure temperature or see the suction pressure to check the superheat;

2. If the superheat of the expansion valve is too small and the liquid supply is too large, the adjusting lever should be rotated clockwise for half a turn or one turn to increase the spring force, reduce the valve opening and reduce the refrigerant flow. The number of turns of the adjusting rod thread at one time should not be too many. When the adjusting rod thread rotates once, the superheat will change by about 1-2.

4. Correct debugging of expansion valve directly affects the cooling effect and energy saving of cold storage. The slow cooling of cold storage is mostly due to improper adjustment of expansion valve. According to the thermodynamic properties of refrigerant, the lower the pressure, the lower the corresponding temperature. The higher the pressure, the higher the corresponding temperature. Among them, the adjustment of expansion valve is the most critical. When the opening of the expansion valve is small, the flow rate of refrigerant passing through is less and the pressure is low. The larger the opening degree of the expansion valve, the more the refrigerant passes through and the higher the pressure.

Third, the expansion valve debugging matters needing attention

The adjustment of expansion valve must be done carefully and patiently. It takes a long time to adjust the pressure, which must be boiled by heat exchange between the evaporator and the reservoir temperature, and then enter the suction cavity of the compressor through the pipeline and be reflected on the pressure gauge. Every time the expansion valve is adjusted, it usually takes 10~15 minutes to stabilize the adjustment pressure of the expansion valve on the suction pressure gauge, and the adjustment should not be rushed. The suction pressure of compressor is the main parameter for adjusting the pressure of expansion valve.

Usually, the filter screen is blocked and the temperature sensitive agent leaks easily. The adjustment response is insensitive, and the adjustment is out of control or unable to be adjusted. When frost appears at the inlet of the expansion valve, or the valve cover is frosted, the temperature of the liquid inlet pipe is lower than normal temperature, or even condensation. The suction pressure of the compressor is lower than the corresponding pressure at the storage temperature, the operating temperature and exhaust temperature of the machine are high, and the cooling temperature drops slowly or cannot drop, which is mostly caused by the blockage of the filter screen of the expansion valve or the blockage of dirty ice.