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What Is The Working Principle Of Expansion Valve?
Feb 26, 2018

Expansion valve structure and working principle 

Thermal expansion valve role:

Thermal expansion valve installed in the evaporator inlet, often referred to as expansion valve, the main role of two:

1) throttling effect: high temperature and high pressure liquid refrigerant throttles through the throttling valve of the expansion valve to become a low temperature and pressure misty hydraulic refrigerant, thereby creating conditions for the evaporation of the refrigerant;

2) control the flow of refrigerant: liquid refrigerant into the evaporator, after the evaporator, the refrigerant evaporated from the liquid state, absorbing heat, reducing the temperature inside the car. Expansion valve to control the flow of refrigerant to ensure that the evaporator outlet is completely gaseous refrigerant, if the flow is too large, the outlet contains liquid refrigerant may enter the compressor to produce liquid hit; if the refrigerant flow is too small, premature evaporation is completed, resulting in Lack of refrigeration

Types of thermal expansion valve:

Thermal expansion valve in accordance with different ways of balance, sub-balance type and external balance; external balance thermal expansion valve F-type and H-type structure of two types.

1) Balanced expansion valve structure and working principle:


Internal balanced F-type thermal expansion valve structure. The temperature of the package filled with refrigerant, placed in the evaporator outlet pipe, the temperature of the package and the upper part of the membrane connected by capillary to feel the evaporator outlet refrigerant temperature, the diaphragm below the pressure is the inlet of the evaporator. If the air-conditioning load increases, the hydraulic refrigerant evaporates in advance of the evaporator is completed, the evaporator outlet refrigerant temperature will rise, the diaphragm pressure increases, pushing the valve stem to expand the opening of the expansion valve, into the evaporator If the air conditioning load decreases, the refrigerant temperature at the outlet of the evaporator will decrease. With the same principle of operation, the valve opening will be reduced and the refrigerant flow will be controlled.

2) External balanced expansion valve structure and working principle:


External balanced expansion valve and internal balanced expansion valve principle is basically the same, the difference is: within the balance of the expansion valve diaphragm is the evaporator inlet pressure; and outside the balance of expansion valve diaphragm is felt below the evaporator Outlet pressure.

3) H-type expansion valve


H-type thermal expansion valve has four interfaces connected with the refrigeration system, two of which are the same as the ordinary thermal expansion valve, one connected to the receiver drier, one connected to the evaporator inlet; the other two interfaces, one connected to the evaporator outlet, one Connect the compressor inlet. The temperature sensing package is located directly in the refrigerant flow at the evaporator outlet. The expansion valve due to the cancellation of the F-type thermal expansion valve in the temperature package, capillary and external balance take over to improve the adjustment sensitivity, compact structure, anti-vibration and reliable.

Direct expansion evaporator.jpg