Relay valves are used to reduce the lag time, both when the brakes are applied and when they’re released. Relay valves are remote-controlled air valves that respond to a control signal from the foot valve. These valves are located near the brake chambers that they operate, and they receive a large volume of air from the service reservoirs. When the brake pedal is pressed, the control signal directs the relay valve to send air to the brake chambers. When the brake pedal is released, the air from the brake chambers is exhausted from a port in the nearby relay valve instead of having to flow back to the foot valve to be exhausted there. Only the air in the control line must flow back to the foot valve.