- A brake which uses air as a working fluid is known as pneumatic brake. The system actuated to apply this phenomenon is know as pneumatic brake system.
- An pneumatic brake system or a compressed air brake system is a type of friction brake for vehicles in which compressed air pressing on a piston is used to apply the pressure to the brake pad needed to stop the vehicle.
Construction of pneumatic braking system
The simplest air brake system consists of
- An air compressor
- A brake valve
- series of brake chambers at the wheels
- unloader valve
- A pressure gauge and a safety valve
- and an air reservoir.
- These are all connected by tubes.
Some air braking systems may have additional components such as
- stop light switch
- low pressure indicator
- An air supply valve to supply air for tyre inflation
- A quick release air quickly from the front brake chambers when the brake pedal is released
- A limiting valve for limiting the maximum pressure in the front brake chambers and a relay valve to help in quick admission and release of air from the rear brake chambers.
Working of pneumatic braking system
- The air compressor operated by the engine forces air at a pressure of 9-10 kscm (kilo standard cubic meters) through the water and oil separator to the air reservoir.
- The air pressure in the reservoir is indicated by a pressure gauge.
- The reservoir contains enough compressed air for several braking operations. From the reservoir the air is supplied to the brake valve.
- As long as brake pedal is not depressed, brake valves stop the passage of air to brake chambers and there is no braking effect.
- When the brake pedal is depressed, the brake valves varies its position and compressed air is admitted into the wheel brake chambers.
- In the chambers the air acts upon flexible diaphragms, moves them the pushes out the rods connected with the levers of the brake gear cams.
- The cams turn and separate the shoes thus braking the wheels.
- When the brake pedal is released, the supply of compressed air is cut off from the brake chambers and they are connected to the atmosphere.
- The pressure in the chambers drops, the brake shoes are returned to their initial position and the wheels run free.
- The brake valve is equipped with a servo mechanism which ensures that the braking force on the shoes is proportional to the force applied to the pedal.
- Besides the valve imparts a relative reaction to the movement of the pedal so that the driver can sense the degree of brake application.
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