 Although the bulb/diaphragm type is used in most systems that control the refrigerant superheat, electronic expansion valves are becoming more common in larger systems or systems with multiple evaporators to allow them to be adjusted independently.Although electronic valves can provide greater control range and flexibility that bulb/diaphragm types cannot provide, they add complexity and points of failure to a system as they require additional temperature & pressure sensors and an electronic control circuit.Most electronic valves use a stepper motor hermetically sealed inside the valve to actuate a needle valve with a screw mechanism, on some units only the stepper rotor is within the hermetic body and is driven through the valve body by stator coils on the outside of the device.