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May Automotive Parts Manufacturing & Supplying Co,.Ltd
May Automotive Parts Manufacturing & Supplying Co,.Ltd

Composition Analysis of Car Expansion Valve


Car expansion valve is composed of three parts: valve body, temperature sensing package and balance pipe.


Valve body of car expansion valve


It is a device used to control the direction, pressure and flow rate of the fluid. The valve is a device that makes the medium (liquid, gas, powder) flow or stop in the piping and equipment, and can control its flow rate.


Temperature sensing package of car expansion valve


The refrigerant filled in the temperature sensing package is in a saturated state of gas-liquid equilibrium, which is not connected with the refrigerant in the system. It is generally bound to the outlet pipe of the evaporator and in close contact with the pipe to sense the superheated steam temperature at the outlet of the evaporator. As the refrigerant inside it is saturated, it transfers the pressure in the saturated state according to the temperature to the valve body.


Common causes of temperature sensing package failure:


When the supply of car expansion valve is more or less in the system, or the valve cannot be closed properly, and the overheating and undercooling temperatures are incorrect, the reason may be that the temperature sensing package is faulty.


  • The capillary tube of the temperature sensing package is broken, causing the filling material in the temperature sensing package to leak, and the correct signal cannot be transmitted to the actuator of the thermal expansion valve.

  • The position of the temperature sensing package is incorrect.


Treatment methods of temperature sensing package failure


In general, the temperature sensing package should be installed on the return air pipe in the horizontal section of the evaporator outlet, away from the suction port of the compressor and close to the evaporator, and it should not be installed vertically. Because installing the temperature sensing package on the upper part of the suction pipe will reduce the sensitivity of the reaction, it may cause too much refrigerant in the evaporator. Installing the temperature sensing package on the bottom of the suction pipe will cause disorder in the supply of liquid, because a small amount of liquid refrigerant always flows to the position where the temperature sensing package is installed, leading to rapid changes in the temperature of the temperature sensing package.


During installation, the temperature sensing package of car expansion valve should be wrapped with copper sheets, and the surface of the return air pipe should be derusted. If it is a steel pipe, after derusting the surface, it should be coated with silver paint to ensure good contact between the temperature sensing package and the return air pipe.


The temperature sensing package must be lower than the upper chamber of the valve top diaphragm, and the head of the temperature sensing package should be placed horizontally or downwards. When the relative position is higher than the upper chamber of the diaphragm, the capillary tube should be bent upward into a U shape to prevent liquid from entering the upper chamber of the diaphragm.


In order to avoid the refrigerant liquid or oil accumulated in the horizontal pipe segment where the temperature sensing package is located when the system suddenly stops, which affects the performance of the temperature sensing package, the pipe segment after the temperature sensing package should be made into.


Balance pipe of car expansion valve


One end of the balance pipe is connected to the outlet of the evaporator slightly away from the position of the temperature sensing package, and is directly connected to the valve body through the capillary. Its function is to transmit the actual pressure at the outlet of the evaporator to the valve body. The valve body has two diaphragms, which move upward under pressure to reduce the flow of refrigerant passing through the expansion valve and seek balance dynamically.

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