Vacuum Pump: Description and Operation

Vacuum pump
In order to ensure that negative pressure is available to the brake servo unit, the car contains a vacuum pump. The pump provides the brake servo unit with negative pressure when the engine cannot properly accommodate the requirement.

The mechanical vacuum pump delivers maximum vacuum irrespective of engine rpm. This means that the pump, in certain situations, delivers more negative pressure than the system uses.

In a situation with an idling engine and a stationary car, the brake pedal may feel "soft" and sink somewhat lower than normal when applied. This is completely normal and will not affect braking force in a negative manner.

The ring type pump, which is lubricated by the engine lubrication system, is mounted on the master cylinder and is driven by the exhaust camshaft. Since it is connected to the camshaft, the speed of the pump is half that of the engine and a negative pressure of 0.8 kPa (0.8 bar) is produced continually for the brake system.