 In such dishwashers the electromechanical rotary switch often used to control the washing cycle is replaced by a microprocessor, but most sensors and valves are still required.However, pressure switches (some dishwashers use a pressure switch and flow meter) are not required in most microprocessor controlled dishwashers as they use the motor and sometimes a rotational position sensor to sense the resistance of water; when it senses there is no cavitation it knows it has the optimal amount of water.A bimetal switch or wax motor opens the detergent door during the wash cycle.