# How does a brake vacuum pump work?



## gemmuj (Feb 22, 2008)

Hi guys,

I would just like to know how a brake vacuum pump works? does it press the brakes with air pressure or can you link the existing braking lines and master cylinder into the vacuum pump.

thank you

Muj


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## elevatorguy (Jul 26, 2007)

For EV applications the vacuum from the engine is replaced with a vacuum pump and usually a added vacuum canister. 
this link explains it a bit. http://www.autoshop101.com/forms/brake05.pdf

Basically, a vacuum booster with a lot of surface area and vacuum assist the driver by adding 3-4 times the applied force, making stopping much easier on the leg muscles.
The hydraulic part of the brakes are separate from the vacuum system.
hope that helps a bit.


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## Coley (Jul 26, 2007)

A vacuum pump is just an air compressor with the inlet and outlet exchanged. You take vacuum from the inlet side of the compressor. The pressure side is just exhausted away.

Inside the power brake booster, is a large diaphragm that is linked to the pushrod from the brake pedal, that also goes into the master cylinder.

A variable valve setup controls the amount of "pull" that is put on this diaphragm. It senses the pressure you have applied to the brake pedal.

The "pull" turns into "push" on the brake rod going into the master cylinder.

The canister, around the diaphragm, is continually under vacuum. 

An extra cannister is usually needed, on an EV, to keep the vacuum level high enough for the electric pump to keep up in heavy (read that "often") stopping, such as in traffic.

On the road, the cannisters, together, keep vacuum at hand and the pump shuts off.

As soon as you apply the brakes, the vacuum level will drop, which signals a switch to once again turn on the vac pump.

Hope this helps.....


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