Vacuum switch

Prior to effective engine computers, engine vacuum was used for many functions in an automobile. Vacuum switches were employed to regulate this flow, and were commonly controlled by temperature, solenoids, mechanically, or directly. They operated vacuum motors, other vacuum switches and other devices.

The engine in a common automobile produces almost 20 inches (51 cm) of vacuum, and this pressure differential may be harnessed for many uses. Engine vacuum is also the best direct source of information on the engine's load. Most delay valves have a one-way function, where there is either no restriction or no movement in one direction.

Types

There are several common types of vacuum switches.

Check valve

A valve that only allows the vacuum signal to move in one direction. Often used with vacuum reservoirs.

Delay valve

A vacuum delay valve is a valve with a small orifice, which delays a vacuum signal. These are commonly used in automobiles to alter the behavior of a vacuum signal. Delay valves are usually color-coded to their function.

Coolant temperature override

Also referred to as a Temperature Vacuum Switch (TVS) or Thermal Vacuum Valve (TVV). The CTO switch measures coolant temperature, usually from a passage in the intake manifold. It was commonly used starting in the 1960s for switching the vacuum advance from ported vacuum to manifold vacuum at high engine temperatures to promote cooler idling. As emissions controls expanded, it gained many other uses.

They commonly have between two and five vacuum ports.

Thermostatically-controlled air cleaner system

The factory air cleaner on carburetored vehicles has a switch controlled by a bi-metallic strip that ultimately selects cool or preheated air. This valve is usually open on one side to the air space within the air filter, and is both temperature controlled, and bleed style. Its function is to keep the air going in to the carburetor above a certain temperature to prevent icing.

Non-Linear vacuum regulator

A NLVR regulates vacuum signal so it is between two vacuum source levels. As one signal increases the other regulator valve switches to another vacuum source.

Bleed valve

A bleed valve controls a metered orifice that adjusts to allow air into the line to weaken a vacuum signal. They are commonly controlled by coolant temperature or under hood air temperature, but may be part of the HVAC system.

Vacuum booster

A vacuum booster uses one vacuum signal, usually ported, to control another signal, usually manifold, that is stronger. It may also use a venturi effect.

Positive crankcase ventilation valve

The Positive Crankcase Ventilation (PCV) is a one-way valve that ensures continual refreshment of the air inside the engine's crankcase.

Vacuum electrical switch

A vacuum switch that turns an electrical connection on or off. Used for early electronic control modules to determine engine load or function.

Vacuum solenoid

An electrical solenoid that switches a vacuum signal on or off.

Manual vacuum switch

Operator controlled switches were often used to control vacuum powered devices before the advent of robust automotive electrical systems or reliable mechanical linkages. They consisted of a variety of shapes, sizes, and configurations much like electrical switches.

They are commonly found as window and HVAC controls.

Electrical Switches

The term "vacuum switch" can also refer to a specialized type of electrical switch in which the contacts are enclosed in a vacuum envelope. This allows the switching of very high voltages with a compact switch, while preventing arcing across the contacts.

ee also

*Manifold vacuum
*List of automotive vacuum devices
*Automobile accessory power

References


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • vacuum switch — vakuuminis jungiklis statusas T sritis automatika atitikmenys: angl. vacuum switch vok. Vakuumschalter, m rus. вакуумный выключатель, m pranc. interrupteur à vide, m …   Automatikos terminų žodynas

  • vacuum switch — See thermal vacuum switch …   Dictionary of automotive terms

  • ported vacuum switch — (PVS) a temperature actuated switch that changes vacuum connections when the coolant temperature changes (originally used to switch spark port vacuum; now used for any vacuum switching function that requires coolant temperature sensing) …   Dictionary of automotive terms

  • choke thermal vacuum switch — (CTVS) a switch used on some GM vehicle to deny vacuum to either the front or the auxiliary choke vacuum breaks. Its purpose is to slow the opening of the choke and to provide better driveability when the engine is cold …   Dictionary of automotive terms

  • oil thermal vacuum switch — (OTVS) a switch used by some GM vehicle to shut off vacuum to the early evaporation (EFE) valve when oil temperature reaches 150° F …   Dictionary of automotive terms

  • thermal vacuum switch — (TVS) [1] measures either air/fuel temperature, underhood temperature, or coolant temperature, or a combination of any two to regulate the EGR valve accordingly. [2] A temperature sensitive switch that shifts the source of the advance from ported …   Dictionary of automotive terms

  • temperature vacuum switch — (TVS) controls vacuum to the EGR valve and/or canister purge valve based on coolant or intake air temperature. Canister purge and EGR do not typically operate when the engine is cold …   Dictionary of automotive terms

  • thermostatic vacuum switch — A temperature sensitive switch which allows spark advance when engine idles for long periods …   Dictionary of automotive terms

  • switch — A device that opens and closes an electric circuit. See actuating switch ambient temperature switch authority Limit Switch battery master switch dimmer switch dipper switch door pillar switch fuel cut off switch fuel pump shut off switch …   Dictionary of automotive terms

  • Vacuum arc — A vacuum arc can arise when the surfaces of metal electrodes in contact with a good vacuum begin to emit electrons either through heating (thermionic emission) or via an electric field that is sufficient to cause field emission. Once initiated, a …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.