Fig. 54. Westinghouse Air Compressor.
Fig. 55 shows the arrangement of the apparatus under the cars of the St. Louis Transit Company. The two storage tanks are each 6 feet long by 18 inches in diameter and are mounted one on each side of the car. Their combined capacity is equivalent to about 100 cubic feet at 45 lbs. pressure. The tanks are charged through an outlet near one side of the car. This outlet contains a check valve and cock to prevent leakage.
The service or low pressure reservoir has a capacity of about 2½ cubic feet. The position of the reducing valve between the high and low pressure valves may be noted in the illustration.
Momentum Brakes. Momentum or friction brakes have been used to some extent both on single-truck and on double-truck cars, but particularly on single-truck cars. They derive the power to operate the brakes from the momentum of the car by means of a friction clutch on the car axle. The difference in various kinds of momentum brakes lies chiefly in the design of the clutch mechanism. The clutch must evidently be arranged to act very smoothly, and must be under very accurate control, as the force with which the brakes are applied depends directly upon the pull exerted by the clutch.
Fig. 55. Arrangement of Storage Air Brake Apparatus.
In the Price momentum brake a flat disc is cast on the car wheel, which is turned off to a smooth surface. Against this disc a friction clutch acts, which has a leather face. The clutch is operated by a motorman’s lever through a set of levers. A small movement in the motorman’s lever forces the clutch against the disc on the car axle. The clutch winds up the brake chain, and thus supplies power to apply the brakes.
Other momentum or friction clutch brakes have been devised, most of which also use an application of leather on iron for the clutch, as this has been found to be most reliable, and to be least affected by the grease and dirt that is liable to work in between the clutch surfaces.
G. E. Electric Brake. The General Electric Company’s electric brake makes use of current generated by the motors acting as dynamos, to stop the car. In order to accomplish this, a brake controller is provided which reverses the armature connections of the motors, and so connects them to operate as dynamos sending current through a resistance in the circuit; the amount of current flowing and the braking effect depending on the car speed and the resistance. In some forms of brake controller, the two controllers are combined in one cylinder, so that the motorman, to apply the electric brake, simply continues the movement of the handle past the “off” position. In others, the brake-controller drum is separate, but is interlocked with the main controller so that it can be used only when the main controller is off.