ELECTRONIC EXPANSION VALVE||EXPANSION VALVE WORKING #WORKING#PRINCIPLE #MEOEXAM#MEP#MOTOR#CLASSW

ELECTRONIC EXPANSION VALVE
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
The electronic signals sent by the controller to the EEV are usually done by a thermistor connected to discharge airflow in the refrigerated case. A thermistor is nothing but a resistor that changes its resistance as its temperature changes. Other sensors are often located at the evaporator inlet and outlet to sense evaporator superheat. This protects the compressor from any liquid floodback under low superheat conditions.
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