Thermally responsive expansion valve

NegotiableUpdate on 03/07

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Overview

When the exhaust temperature and lubricating oil temperature of the refrigeration unit are too high, the temperature responsive expansion valve opens, and the liquid refrigerant is throttled and cooled through the valve before being injected into the suction end and compression chamber of the compressor, respectively cooling the coil of the motor, the mixture of refrigerant and lubricating oil, so that the liquid refrigerant entering the evaporator has a lower temperature.

Product Details

　　Composition of thermal responsive expansion valve:

It is an important component in the refrigeration system, usually installed between the liquid storage tank and the evaporator. Simply put, an expansion valve consists of three main parts: a valve body, a temperature sensing bulb, and a balance pipe.

temperature sensing bulb

The temperature sensing bulb is filled with refrigerant that is in a state of gas-liquid equilibrium saturation, which is not connected to the refrigerant in the system. It is usually tied to the outlet pipe of the evaporator, in close contact with the pipe to feel the temperature of the superheated vapor at the outlet of the evaporator. Since the refrigerant inside is saturated, it transmits the pressure of the saturated state to the valve body based on the temperature.

balance pipe

One end of the balance tube is connected to the evaporator outlet slightly away from the temperature sensing bulb, and is directly connected to the valve body through a capillary tube. The function is to transmit the actual pressure at the outlet of the evaporator to the valve body. There are two diaphragms inside the valve body, which are oriented under pressure Moving upwards reduces the flow of refrigerant through the expansion valve, seeking balance dynamically.

　　Correct adjustment method for thermal responsive expansion valve:

1) Before adjusting the thermal expansion valve, it is necessary to confirm that the abnormal refrigeration of the cold storage is caused by the deviation of the thermal expansion valve from the optimal working point, rather than other reasons such as low Freon, clogged drying filter, filter screen, fan, belt, etc. At the same time, it is necessary to ensure the correctness of the sampling signal of the temperature sensor, and the installation position of the temperature sensor must be correct. It cannot be installed directly below the pipeline to prevent factors such as oil accumulation at the bottom of the pipe from affecting the correct temperature sensing of the temperature sensor.

(2) Precautions for adjustment

The adjustment of the thermal expansion valve must be carried out under normal operation of the refrigeration system. Due to the inability to place a thermometer on the surface of the evaporator, the suction pressure of the compressor can be used as the saturation pressure inside the evaporator to obtain an approximate evaporation temperature by looking up a table. Measure the temperature of the return pipe with a thermometer and compare it with the evaporation temperature to verify the degree of superheat. During adjustment, if you feel that the overheating is too low, you can rotate the adjustment screw clockwise (i.e. increase the spring force and decrease the opening degree of the thermal expansion valve) to reduce the flow rate; On the contrary, if you feel that the overheating is too high, that is, the liquid supply is insufficient, you can rotate the adjusting screw in the opposite direction (counterclockwise) to increase the flow rate. Due to the thermal inertia of the thermal expansion valve temperature sensing system in practical work, signal transmission lags behind, and the next adjustment can only be made after the operation is basically stable. Therefore, the entire adjustment process must be patient and meticulous, and the number of rotations of the adjusting screw should not be too many or too fast at once.