A relay valve is a type of pneumatic valve

A relay valve is a type of pneumatic valve used in air brake systems for heavy-duty vehicles such as trucks and buses. It works by controlling the flow of compressed air to the brake chambers located on the vehicle's wheels.
The relay valve is typically mounted on the vehicle's frame rail and receives compressed air from the vehicle's air compressor. The valve has two main ports, one for the supply of compressed air and one for the delivery of air to the brake chambers. The valve also has a control port that receives air pressure signals from the brake pedal or other control devices.
When the driver applies the brake pedal, air pressure from the control port is used to activate the valve, which then opens the supply port and allows compressed air to flow to the brake chambers. This causes the brake shoes or pads to be pressed against the wheels, creating friction and slowing down the vehicle.
Relay valves are important components of air brake systems because they allow for precise and consistent control of braking forces across all wheels of the vehicle. They also help to ensure that the brakes are applied evenly, reducing the risk of skidding or loss of control.
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