Williams 106841 WM674A Dual Function Parking Break Control

The WM674 is a dual function valve used to control spring brakes under normal and emergency conditions. Each WM674 unit consists of two manually operated three-way valves housed in a common body. When pressure at its inlet exceeds 45 PSI (310 kPa), the first valve (square button) which is spring-loaded so supply pressure can flow through it to release the spring breaks and charge the emergency supply tank. If supply pressure falls between 20-35 PSI, the first valve automatically closes and exhausts downstream pressure to cause emergency application of the spring brakes. An integral check valve in the second valve protects pressure in the emergency supply tank. The second valve can be applied to allow air to flow from the tank so the springs so the vehicle can be moved. Since the second valve's function is for temporary emergency use, the round button must be manually held down. As soon as the button is released, pressure at the outlet is exhausted to atmosphere and spring brakes are reapplied.

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