The purpose of the expansion valve in a refrigeration system is to regulate the flow of refrigerant from the high-pressure side (condenser) to the low-pressure side (evaporator), ensuring efficient operation based on the cooling demand. It adjusts refrigerant flow to maintain the desired temperature in the evaporator. It prevents liquid refrigerant from reaching the compressor, ensuring complete vaporisation in the evaporator.

Pressure Regulation: The valve contains a diaphragm that responds to pressure differences:

• P1 (Top Pressure): Exerted by a heat-sensitive fluid in a bulb, which senses the temperature of the gas leaving the evaporator.
• P2 (Bottom Pressure): Exerted by the refrigerant entering the evaporator.
• P3 (Spring Pressure): Ensures a degree of superheat, keeping the valve slightly closed to convert all liquid refrigerant into gas.
• At superheat conditions, P1 = P2 + P3.
• An Adjusting Screw is used to modify the superheat degree, optimizing the evaporator’s performance.

Equalizing Line: In systems with a significant pressure drop in the evaporator (more than 0.3 bar), an Equalizing Line feeds the outlet pressure back to the valve for accurate temperature and pressure control.

• Ensures efficient heat absorption in the evaporator.
• Protects the compressor by avoiding liquid refrigerant carryover.
• Adapts to varying cooling loads for optimal system performance.