Vacuum
A commonly available source of power from an internal combustion engine is the partial vacuum available at the intake manifold. The piston engine is fundamentally an air pump, and it produces suction and partial manifold vacuum.
Manifold vacuum varies depending on engine load and throttle position, and automobiles use vacuum reservoirs or "vacuum canisters" to provide a usable source under varying conditions. Turbo charged and super charged engines do not always produce vacuum; the intake manifold is actually pressurized when the turbo is spinning above a certain speed.
Reservoirs and devices connected to the engine through check valves allow pressure to reduce when the engine is generating a lot of vacuum, but do not allow air back in. Vacuum canisters only allow vacuum accessories to be operated for a very short time, and air will leak in after the engine turns off.
The most ubiquitous vacuum-powered accessory is the booster for the power brake system. The vacuum is only an assist and the brakes can still function, requiring greater force, if the booster vacuum is used up.
Many older vehicles used vacuum-powered windshield wipers. Loss of manifold vacuum when the engine was working hard, or at wide open throttle, necessitated using a vacuum booster pump which was usually part of the fuel pump.
Automotive vacuum systems reached their height of use between the 1960s and 1980s. During this time a huge variety of vacuum switches, delay valves and accessory devices were created.
As an example, a 1967 Ford Thunderbird used vacuum for:
- Power brakes
- Transmission shift control
- Doors for the hidden headlamps
- Remote trunk latch release
- Rear cabin vent control
- Power door locks
- Ventilation air routing
- Control of the heater core valve
- Tilt-away steering wheel release
Such systems tend to be unreliable with age as the vacuum tubing becomes brittle and susceptible to leaks.
Read more about this topic: Automobile Accessory Power
Famous quotes containing the word vacuum:
“Teenagers who are never required to vacuum are living in one.”
—Fred G. Gosman (20th century)
“No, it wasn’t an accident, I didn’t say that. It was carefully planned, down to the tiniest mechanical and emotional detail. But it was a mistake. It was a beaut. In the end, somehow granted the time for examination, we shall find that our so-called civilization was gloriously destroyed by a handful of vacuum tubes and transistors. Probably faulty.”
—John Paxton (1911–1985)