The hand brake of a bus applies pressure only on the rear axle wheels using a spring actuated cylinder. But how exactly a parking brake works? how can the working be related to a service brake system?
HELLO.....
As i know the control system is divided into two service brake circuits, the parking brake circuit, and the trailer brake circuit. The dual service brake circuits are further divided into front and rear wheel circuits which receive compressed air from their individual reservoirs for added safety in case of an air leak. The service brakes are applied by means of a brake pedal air valve which regulates both circuits. The parking brake is the air operated spring brake type where its applied by spring force in the spring brake cylinder and released by compressed air via hand control valve. The trailer brake consists of a direct two line system: the supply line (marked red) and the separate control or service line. The supply line receives air from the prime mover park brake air tank via a park brake relay valve and the control line is regulated via the trailer brake relay valve. The operating signals for the relay are provided by the prime mover brake pedal air valve, trailer service brake hand control (subject to local heavy vehicle) and the prime mover park brake hand control.
The pneumatic park brake works with the help of a large spring which allows the braking mechanism to work. The spring is countered by a cylinder which is operated by an engine powered air pump. As a result, all the pressure is released by the spring on the brake, so that the wheel can move freely. When the air escapes the system by making the psshh sound, the spring pressure applies to the brake again. This is normally done by the drivers.
when you applied hand brake compressed air from master cylinder moves in brake cylinder and piston moves forward direction brakes shoes are expanded
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