Brake Tests

42 (a) The predetermined rate of reduction of equalizing reservoir pressure, as determined by the preliminary exhaust port in the engi- neer’s brake valve, which is 20 pounds reduction in from 5% to 62 seconds.. (b) The length of train. With a train length such that the out- flow from the brake pipe exhaust at the engineer’s brake valve can reduce the brake pipe at the same rate that the equalizing reservoir is being reduced through the preliminary exhaust, the rate of pre- liminary exhaust governs the rate of application of the brakes on the train. When the train is longer, however, this is not possible and t e rate of brake pipe reduction and consequently of brake application on any car is determined by the length of train and by the amount of brake pipe leakage as mentioned in the following paragraph. (c) The leakage of air from the brake pipe can affect the rate ° brake application only when the train is longer than will permit the rate of brake pipe reduction to be controlled in accordance with the rate of preliminary exhaust. 82. The maximum brake cylinder pressure obtainable in service is limited by a high-speed reducing valve attached directly to the brake cylinder. This is designed to operate as a safety valve during service operations and prevents the brake cylinder pressure from rising above the predetermined amount, viz.: 62 pounds. The brake can be graduated on in steps or a full service application can be made at once as desired. RELEASING AND RECHARGING. 83. When the brake pipe pressure is increased above that of the auxiliary reservoir the triple valve operates so as to:- (a) Connect the brake cylinder to the atmosphere through the release cavity in the triple valve slide valve, thus releasing the brakes. (b) Connect the brake pipe to the auxiliary reservoir through the feed groove around the triple valve piston and so permit the auxiliary reservoir to be recharged..,, After having moved to release position the triple valve piston remains there until a subsequent reduction of brake pipe pressure below the auxiliary reservoir pressure. Consequently, no graduation of the release is possible. 84 The certainty of releasing all brakes in the train depends on the possibility of establishing the differential pressure required to move the triple valve parts to release position. No difficulty is experienced in this direction so far as the cars at the head end of the tram are con- cerned, but the increase in brake pipe pressure is necessarily slower at the rear than at the head end. Large auxiliary reservoir volumes, • . « large amount of air for recharging (all of which must be requiring a large amount