Some trucks, especially heavy trucks, have a relatively large clutch pressing force. In order to reduce the force of the driver to step on the clutch pedal, a clutch booster is usually used, also called a clutch booster cylinder and a booster pump. This device uses both a cylinder and an oil cylinder, so there are cards Youhui thinks this is similar to the principle of gas-top oil brakes, but in fact the principles of the two mechanisms are quite different.
The gas-top oil brake is also called the gas-push oil brake and the gas-top hydraulic brake system. It has both pneumatic and hydraulic devices at the same time.
The brake air chamber and the hydraulic master cylinder are connected in series. By converting the air pressure energy into hydraulic energy, the brake fluid is transmitted to each wheel cylinder, thereby producing a braking effect.
Compared with the pure air brake, the brake air chamber in the air-to-liquid system is smaller in volume and relatively compact in layout.
In addition, the air-top hydraulic brake system has these advantages:
1. The length of the air pressure system pipeline is short, which can reduce the lag time;
2. The hydraulic wheel cylinder as the actuator is light in weight;
3. When towing a trailer, the trailer can choose air brake or hydraulic brake.

Air top oil braking system
According to the experience of some old car owners, the air-top oil brake does have a good braking force, and the response is fast, and it will not be as violent as the braking force of the air brake, but it also has disadvantages.
The high temperature of the long downhill will reduce the performance of the brake fluid, and the sealing cup of the hydraulic wheel cylinder (wheel cylinder) will also melt or even fall off, resulting in the leakage of the brake fluid and flying, which makes people feel that the braking force is gone.
In addition, the long-term maintenance and braking of the brake drum are also particularly annoying. After all, the reliability is not comparable to the pure air brake with a relatively simple structure. Nowadays, it is difficult to find air-over-hydraulic brake systems except in vehicles such as loaders and dump trucks that require hydraulic systems.
In addition, a clutch booster on a truck is often referred to as gas cap oil, which is in fact inaccurate.

clutch booster
Some trucks, especially medium and heavy trucks, have a relatively large clutch pressing force. In order to reduce the force of the driver stepping on the clutch pedal, a clutch booster, also called a clutch booster cylinder and a booster pump, is usually used. Friends will think that this is similar to the principle of gas-top oil brakes, but in fact the principles of the two mechanisms are quite different.
The clutch mechanism uses the brake fluid as the medium, starts from the clutch pedal, and finally transmits the force to the clutch fork, which acts on the release bearing, presses down the pressure plate diaphragm to separate the pressure plate and the clutch plate, and interrupts the transmission.

General unassisted hydraulic clutch mechanism:
Pedal - Clutch Master Cylinder (Hydraulic) - Oil Pipe - Clutch Slave Cylinder (Hydraulic) - Clutch Fork

Clutch mechanism with clutch assistant cylinder:
Pedal - clutch master cylinder (hydraulic) - oil pipe - clutch booster cylinder (gas-liquid integrated) - clutch fork
When friends add a clutch booster pump to some light trucks, they need to pay attention to two issues, one is to have an air storage tank (required for air brake type), and the other is to have enough installation space, there are cylinder diameters ranging from 70mm to 120mm on the market. For different clutch booster pumps, light trucks generally use small bores.
Some people may say that it is better to use air pressure directly for the clutch? But from using the air brake, you can feel that the controllability of air pressure is not very good, and the clutch requires semi-linked control, so it is not realistic to use pure air pressure.
To sum up, the air-cap oil brake is a mechanism that uses the hydraulic pressure to perform the braking through the series connection of the air chamber and the hydraulic cylinder, while the clutch booster cylinder is a gas-liquid integrated component that uses air pressure to assist. For gas cap oil.