A metering valve is a device found in the braking systems of vehicles with rear drum brakes and front disc brakes. The valve controls the distribution of pressure to the brakes to stabilize the car during braking, increase braking efficiency, and make braking safer. Metering valves are located at various points in the braking system, depending on the make and model, and may be part of a larger combination valve used to regulate pressure inside the hydraulic braking system.
When people apply the brakes in a car, they activate a hydraulic system that multiplies the pressure of their feet. A light tap on the brake pedal can translate into substantial pressure inside the braking system, allowing people to slow or stop the car. In a car with front disc brakes and rear drum brakes, if the pressure from the brake pedal went straight to the brakes, the front brakes would activate first, and this could make the car unstable.
If the front brakes kick into operation first, there is a risk that the rear of the car could fishtail or that other stability problems could develop. In a car with a metering valve, the valve diverts the initial pressure to the rear brakes, and once they kick in, pressure can be released to the front brakes and allowed to equalize. This happens within a very short period of time, and it can feel like the brakes are activating simultaneously.
Metering valves in cars compensate for the fact that disc brakes tend to activate more quickly and be more sensitive. In cars with other types of brake systems, a metering valve may not be necessary, or a different type of system will be used to control braking pressure so that the driver can apply the brakes safely. The metering valve works with a series of interconnected systems to keep the brakes working smoothly and properly when they are needed.
When brakes are checked, the mechanic may inspect the metering valve to confirm it is in good working order. If necessary, the valve can be cleaned or replaced. It is also important to remember to fully drain and clean the valve when the brake system is being flushed, and to properly reconnect all of the components of the braking system after work is finished. There may be special considerations with systems in individual cars as a result of unusual design features, including features intended to increase safety and efficiency.