Structure and working principle of expansion valve
1 The role of thermal expansion valve:
The thermal expansion valve is installed at the inlet of the evaporator, often called the expansion valve, and has two main functions:
1) Throttling function: After the high-temperature and high-pressure liquid refrigerant is throttled through the orifice of the expansion valve, it becomes a low-temperature and low-pressure mist-like hydraulic refrigerant, which creates conditions for the evaporation of the refrigerant;
2) Control the flow rate of the refrigerant: the liquid refrigerant entering the evaporator, after passing through the evaporator, the refrigerant evaporates from the liquid state to the gaseous state, absorbs heat, and reduces the temperature in the vehicle. The expansion valve controls the flow of refrigerant to ensure that the outlet of the evaporator is completely gaseous refrigerant. If the flow is too large, the outlet contains liquid refrigerant, which may enter the compressor to produce liquid shock; if the refrigerant flow is too small, the evaporation is completed in advance, resulting Insufficient cooling;
2 Types of thermal expansion valve:
The thermal expansion valve is divided into an internal balance type and an external balance type according to the balance mode; the external balance type thermal expansion valve is divided into two structural types: F type and H type.
1) Structure and working principle of internal balance expansion valve:
Internal balance type F thermal expansion valve structure diagram
Structure diagram of internal balance type F thermal expansion valve. The temperature-sensing package is filled with refrigerant and placed on the outlet pipe of the evaporator. The temperature-sensing package is connected to the upper part of the diaphragm through a capillary tube to sense the refrigerant temperature at the outlet of the evaporator. The pressure at the bottom of the diaphragm is the inlet pressure of the evaporator. If the air conditioning load increases and the hydraulic refrigerant evaporates in advance in the evaporator, the refrigerant temperature at the outlet of the evaporator will rise, the pressure on the diaphragm will increase, and the valve stem will be pushed to increase the opening of the expansion valve and enter the evaporator. The refrigerant flow rate increases and the cooling capacity increases; if the air-conditioning load decreases, the refrigerant temperature at the outlet of the evaporator decreases, and the valve opening degree is reduced by the same action principle, thereby controlling the refrigerant flow rate.
2) Structure and working principle of external balance expansion valve:
The pressure under the diaphragm is the outlet pressure of the evaporator.
The principle of the external balanced expansion valve is basically the same as that of the balanced expansion valve, the difference is:
Under the diaphragm of the inner balance expansion valve, the inlet pressure of the evaporator is felt; while under the diaphragm of the outer balance expansion valve, the outlet pressure of the evaporator is felt.
3) H-type expansion valve
The H-type thermal expansion valve has four ports connected to the refrigeration system, two of which are the same as ordinary thermal expansion valves, one is connected to the storage dryer and the other is connected to the evaporator inlet; the other two are connected to the outlet of the evaporator and one Connect the compressor inlet. The temperature sensing bag is directly in the refrigerant gas flow at the outlet of the evaporator. The expansion valve eliminates the temperature-sensing package, capillary tube and external balance connection in the F-type thermal expansion valve, which improves the adjustment sensitivity, has a compact structure and reliable vibration resistance.
1 From filter dryer 2 To evaporator 3 From evaporator 4 To compressor 5 Measuring hole 6 Ball 7 Spring 8 Movable foot 9 Refrigerant 10 Pressure compensation under the membrane 11 Metal membrane 12 Temperature sensing element
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