What must occur across a metering valve for it to be classified as an actual expansion valve?

For a metering valve to be classified as an actual expansion valve, there must be a specific set of changes occurring in the refrigerant as it passes through. The correct choice involves a pressure drop, a temperature drop, and an increase in velocity.

When refrigerant flows through an expansion valve, it is subjected to a reduction in pressure, which leads to a drop in its temperature as it transitions from a high-pressure area to a low-pressure area. This phenomenon is due to the thermodynamic principles governing phase changes and the associated enthalpy changes of the refrigerant. As the pressure drops, the refrigerant expands and cools, resulting in a lower temperature.

Additionally, the design of the expansion valve allows for an increase in velocity as the refrigerant exits the valve into the evaporator coil. This increase in velocity is essential for effective heat exchange in the evaporator, facilitating the refrigerant's absorption of heat from the surrounding environment.

In summary, the correct answer encapsulates the critical thermodynamic changes that define the operation of an actual expansion valve, which are essential for the proper functioning of a refrigeration cycle.