- General vacuum pump
- vane pump
- diaphragm pump
This page is about the brake booster vacuum pump. More information about the brake booster can be found on the page brake booster. There is also the same story about the vacuum pump.
The required negative pressure (vacuum) for a vacuum brake booster is often obtained by the engine vacuum in a petrol engine. A hose runs from the brake booster to the intake manifold. Because an underpressure prevails in the intake manifold, an underpressure is also extracted from the exciter. When the engine is turned off and the brake pedal is pumped several times, the pedal will feel hard. This is because all the vacuum has disappeared from the brake booster. When the engine is started again, the pedal will drop again and it will be possible to press further. It must therefore always be taken into account when a vehicle is towed; in the car with the engine not running, 3 to 4 times as much force will have to be exerted on the pedal. Also, the power steering will not work. It is therefore wise to drive slowly.
It is possible that the pedal feels hard immediately after switching off the engine; it seems as if the vacuum immediately falls away. This could be due to a ruptured vacuum hose between the brake booster and the engine, or a faulty return valve in the hose. This is usually a round piece of plastic between 2 parts of the hose.
If the relevant hose is torn, it must be replaced as soon as possible. If it further tears or breaks, the complete power brakes will fail.
With the newer petrol engine techniques (with high pressure injection / lean mixture), turbo engines and with none with a diesel engine, it is not possible to obtain sufficient underpressure from the intake manifold, because these work with an air surplus (a maximum amount of air is then always supplied). ), which means that a separate vacuum pump is required. There are 2 different vacuum pumps, namely the vane pump and the diaphragm pump. The vane pump is also called the tandem pump or the vacuum pump.
The vane pump is the most commonly used pump for obtaining underpressure in the brake booster. Often this pump is mounted directly on the back of the camshaft on the cylinder head, but it can also be driven by the Multi / V-belt or alternator.
The operation is as follows; when a stiffener (in the picture red) rotates past the entrance of the pump, the space behind the stiffener expands. The yellow spring presses the partition against the wall, making this space larger and larger. A negative pressure is now generated in the space with the blue arrows. As the pump continues to run, the air (indicated by the red arrow) is vented to the engine crankcase or valve cover.
The diaphragm pump is placed between the vacuum brake booster and the intake manifold, engine crankcase or valve cover. The movement of this pump is similar to the movement of the piston, connecting rod and crankshaft on the car engine. On the down stroke (left) the space above the diaphragm expands and the valve is sucked down. Air will now flow from the brake booster (blue) into the pump. When the piston moves back up, the right valve opens (right image). The air is now discharged to the engine crankcase or valve cover previously.