9.6.7 EXV/EEV
The electronic expansion valve (EEV) operates with a much more sophisticated design.
EEVs control the flow of refrigerant entering a direct expansion evaporator. They do this in response
to signals sent to them by an electronic controller. A small motor is used to open and close the valve
port. The motor is called a step or stepper motor. Step motors do not rotate continuously. They are
controlled by an electronic controller and rotate a fraction of a revolution for each signal sent to them
by the electronic controller. The step motor is driven by a gear train, which positions a pin in a port in
which refrigerant flows. A cutaway of an EEV with step motor and drive assembly is shown in
reference Figure. Step motors can run at defined steps per second and can return to their exact
position very quickly. The controller remembers the number of step signals sent by the controller. This
makes it possible for the controller to return the valve to any previous position at any time. This gives
the valve very accurate control of refrigerant that flows through it.
To Next Page
Loading...
