It can be roughly divided into direct acting vacuum assist and hydraulic vacuum assist. Because the direct-acting vacuum boost directly assists the pedaling force, and the brake operation feeling is good, it is widely used in cars and small-sized cargo vehicles. However, because the toe-down force is directly used as a booster, it is restricted by the installation space. The hydraulic vacuum assist is to use the master cylinder to generate hydraulic pressure to assist, so it can be installed anywhere between the master cylinder and the wheel cylinder, but the brake operation feeling is generally worse than the direct action vacuum boost.
The power source of the booster device uses the negative pressure of the engine intake manifold (gasoline engine vehicle) or the negative pressure of the vacuum pump (mainly diesel engine vehicle).
The check valve between the booster and the negative pressure source must be fitted with a check valve. The check valve can maintain a high vacuum while reducing negative pressure variation in the booster. In addition, in gasoline engine vehicles, in order to prevent gasoline from flowing into the booster, a check valve is generally installed between the engine intake manifold and the booster. To prevent the gasoline in the hose from flowing into the booster device, the check valve is installed at the highest point of the hose, or it is installed near the highest point by a section of the engine.