What is Air Brake Relay Valve? (air brake system)

A relay valve is an air-operated valve commonly used in air brake systems for heavy trucks and semi-trailers in tractor-trailer combinations. Its primary purpose is to remotely control the brakes at the rear of these vehicles. Let me explain further:
Function:
In heavy trucks, air takes longer to travel to the rear of the vehicle than to the front. This delay can cause a condition known as brake lag.
To address this, relay valves are installed near the rear service brake chambers. They speed up the application and release of the rear brakes.
When a driver presses the brake pedal, the relay valve receives a signal. It then allows air to enter the brake chamber via an air inlet.
The diaphragm inside the relay valve gets pushed, activating a series of components that ultimately apply the rear brakes.
Tractor-Trailer System:
In tractor-trailer combinations, a remote air supply is provided for service brake application.
For tractors and straight trucks, a large-diameter pipe connects the primary reservoir to the relay valve.
In trailers, this remote air supply comes from a tank charged whenever the emergency brakes are released via the red trailer-supply valve.
The merged air from both the primary and secondary reservoirs of the tractor prevents air loss from one braking circuit, ensuring better control.
Safety and Control:
The relay valve ensures that the rear brakes work in conjunction with the front ones, allowing larger vehicles to stop effectively.
In newer vehicles, the relay valve is connected to the brake pedal and the rear brakes through various series of wires, controlled by a central unit 12.
Remember, relay valves play a crucial role in maintaining safe braking performance for heavy trucks and trailers

[@bimalnandana9679]

Thank you for clear explanation .👍❤

[@mixAUTOTECH]

Glad it was helpful!