Brake Tests

56 emergency reservoir to recharge the service reservoir in addition to the auxiliary reservoir. Not until the pressures in all these reservoirs are nearly equalized does the equalizing piston move to its full release position and permit air to flow from the brake pipe, but when this does occur air from the brake pipe then completes the recharging of all the reservoirs up to normal brake pipe pressure. In this way all the air supplied to the brake pipe through the engineer’s brake valve during the early stages of the release is effective in raising the brake pipe pres- sure and uniformly releasing all of the brakes. Graduated Release Cap in Direct Release Position. 119. In recharging after a service brake application, the auxiliary reservoir pressure is increased by air flowing to it from the brake pipe only, no air being supplied to the auxiliary reservoir from the emergency reservoir when the graduated release cap is in direct release position. However, when the auxiliary reservoir pressure has been increased to within about five pounds of the normal running brake pipe pressure the service reservoir charging valve operates and permits air from the emergency reservoir to flow to the service reservoir. This assists in recharging this reservoir and in doing so relieves the brake pipe of the necessity for supplying air to recharge the larger reservoir volume during the time the brakes should be releasing. Thus, even with the graduated release cap in direct release position the air supplied to the brake pipe is made effective in producing a prompt and certain release of all the brakes in the train. Pneumatic Service Brake APPLICATION. 120. In response to a given reduction in brake pipe pressure the equalizing portion of the universal valve automatically reduces the pressure in the service and auxiliary reservoirs (which are connected when the equalizing parts are in service position, but separated when they are in release position), an equal amount. The total amount of compressed air thus measured out from the auxiliary and service reservoirs is delivered to the brake cylinder, where it produces a pressure on the brake cylinder piston proportional to the volume it occupies as determined by the piston travel. 121. The amount of brake cylinder pressure and braking power corresponding to various brake pipe reductions are shown by the full line *n Fig. 25. It will be noted that this curve does not coincide with the dotted curve as explained in Par. 80, in connection witli the PM equipment with large size auxiliary reservoirs. This is because the UC equipment is designed to give an equalization pressure of 50 pounds per square inch with 8-inch piston travel; and, furthermore, the braking power basis is .90 per cent, with 60-pound brake cylinder pressure instead of 80 per cent, with the PM equipment.