Unit 5
Direct-expansion(DX)system|A system in which the required cooling effect is achieved by the expansion of a refrigerant from a liquid to a vapor state.
Externally equalized|Describes an expansion valve that has a connection to the suction line downstream of the evaporator coil to serve as a closing force. External equalizers are used when there is a significant pressure drop through the evaporator.
Flash gas|The refrigerant vapor that forms as the results of a rapid change from its liquid state due to a reduced pressure condition.
Hunting|Describes the operation of an expansion valve opening and closing excessively and repeatedly, unable to stabilize at a consistent flow rate.
Internally equalized|Describes an expansion valve that uses pressure value at its own outlet to the evaporator coil to serve as a closing force.
Piston|A component of a fixed-orifice metering device that contains the orifice. The piston is free to move back and forth inside its housing. At one end of its travel, it meters refrigerant flow through the orifice; at the other end, it allows refrigerant to flow both through the orifice and around its outside perimeter.
Stepper motor|A type of motor used to open and close an electronically controlled expansion valve. The motor rotates in very small increments called steps, based on signals received from an external controller.
Thermostatic element|An assembly filled with refirgerant in saturation with an attached sensing bulb that converts the heat from the suction into a pressure value. This pressure acts as the opening force in a thermostatic expansion valve. It is also referred to as a power element.