Westinghouse S-3 Straight Air Valve

The Westinghouse S-3 was used in the early D&RG(W) combined straight and automatic air systems. This system allows the engineer to apply the tender and train brakes using the automatic brake valve without applying the driving wheel brakes. It enables the independent operation of the locomotive and tender brakes, admitting air from the main reservoir through a reducing valve and then directly to the brake cylinders. The S-3 allows the engineer to apply, lap, and release air from the cylinders up to the pressure setting of the reducing valve (typically 45 PSI).