Vacuum Switch
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Prior to effective
engine control unit An engine control unit (ECU), also called an engine control module (ECM), is a device that controls various subsystems of an internal combustion engine. Systems commonly controlled by an ECU include the fuel injection and ignition systems. The ...
computers, vacuum switches were employed to regulate the flow of engine vacuums in
automobiles A car, or an automobile, is a motor vehicle with wheels. Most definitions of cars state that they run primarily on roads, Car seat, seat one to eight people, have four wheels, and mainly transport private transport#Personal transport, peopl ...
. For instance, a dual port vacuum switch located in a port on the
intake manifold An inlet manifold or intake manifold (in American English) is the part of an internal combustion engine that supplies the fuel/air mixture to the cylinder (engine), cylinders. The word ''manifold (engineering), manifold'' comes from the Old Eng ...
would monitor the
coolant A coolant is a substance, typically liquid, that is used to reduce or regulate the temperature of a system. An ideal coolant has high thermal capacity, low viscosity, is low-cost, non-toxic, chemically inert and neither causes nor promotes corr ...
temperature in the coolant crossover. It received vacuum (port E on the switch) from the
carburetor A carburetor (also spelled carburettor or carburetter) is a device used by a gasoline internal combustion engine to control and mix air and fuel entering the engine. The primary method of adding fuel to the intake air is through the Ventu ...
. The vacuum flowed through the switch to a vacuum
solenoid upright=1.20, An illustration of a solenoid upright=1.20, Magnetic field created by a seven-loop solenoid (cross-sectional view) described using field lines A solenoid () is a type of electromagnet formed by a helix, helical coil of wire whos ...
such as a heat riser used to restrict exhaust, allowing the engine to heat up faster. When the coolant heated to operating temperature, the vacuum switch closed off the port (port S), turning off the vacuum to the heat riser. The result clears the exhaust restriction. The switch monitored the temperature, and performed its designed function under optimal conditions.


See also

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Automobile accessory power ] Automobile accessory power can be transferred by several different means. However, it is always ultimately derived from the automobile's internal combustion engine, battery, or other "prime mover" source of energy. The advent of high-powered b ...
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Manifold vacuum Manifold vacuum, or engine vacuum in a petrol engine is the difference in air pressure between the engine's intake manifold and Earth's atmosphere. Manifold vacuum is an effect of a piston's movement on the induction stroke and the airflow thr ...
Switches {{automotive-part-stub