A reversing valve is a component of a heat pump that reverses the refrigerant's direction of flow, allowing the heat pump to switch from cooling to heating or heating to cooling. The reversing valve is a heat pump's sole way of switching between heating and cooling modes.

 

Although essential, reversing valves lower the efficiency of a heat pump for three main reasons:

 

Heat transfer between the hot and cold gases flowing through the valve

Pressure drops across the valve caused by bends and sharp entrances and exits

Refrigerant leakage from the high pressure side to the low pressure side of the valve (through clearance between the slider and seat)