1. The most common source is the intake manifold. As the piston moves down during the intake stroke, it creates a low-pressure area in the intake manifold. This low pressure draws air and fuel into the cylinder through the intake valve. The vacuum created in the intake manifold is also used to operate the brake booster.
2. Some gasoline engines use a vacuum pump mounted on the engine to create vacuum for the brake booster. This type of vacuum pump is typically used on engines with a high-pressure direct injection (HDI) fuel system. HDI systems require a higher vacuum level than can be provided by the intake manifold.
For diesel engines:
1. The primary source of vacuum for diesel engines is the vacuum pump. The vacuum pump is driven by the engine and creates a vacuum that is used to operate the brake booster.
2. Some diesel engines also use an exhaust gas recirculation (EGR) valve to create vacuum for the brake booster. The EGR valve opens during the exhaust stroke and allows a small amount of exhaust gas to flow back into the intake manifold. This exhaust gas helps to reduce the pressure in the intake manifold and creates a vacuum that is used to operate the brake booster.
