Prior to effective
engine control unit computers,
engine vacuum was used for many functions in an
automobile
A car or automobile is a motor vehicle with wheels. Most definitions of ''cars'' say that they run primarily on roads, seat one to eight people, have four wheels, and mainly transport people instead of goods.
The year 1886 is regarde ...
. Vacuum switches were employed to regulate this flow. For instance a dual port vacuum switch located in a port on the intake manifold monitored the coolant temperature in the coolant crossover. It received vacuum (port E on the switch) from the carburetor. The vacuum flowed through the switch to a vacuum solenoid (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 on the vacuum switch) turning off the vacuum to the heat riser. The result is to clear the exhaust restriction. The switch monitored the temperature and when conditions were right it performed its designed function.
See also
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Manifold vacuum
Manifold vacuum, or engine vacuum in an internal combustion 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 ...
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Automobile accessory power
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Switches