High Pressures in a New Brake
Page 37
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Details of the Latest Westinghouse Brake for Road Vehicles, which has a Storage Pressure of 450 lb. per sq. in. and is of Light Weight
MO meet the present-day require/ ments of efficient power braking for heavy commercial vehicles without introducing apparatus that is excessively heavy, the Westinghouse Brake and Saxby Signal Co., Ltd., 82, York Road, King's Cross, London, N.1, has produced a new form of equipment in which the interesting principle is adopted of using high-pressure compressed air, with correspondingly small reservoir, application cylinders, pipes, etc. This allows the brake cylinders to be easily mounted on the axle, thus eliminating rods and mechanical brake gear, also providing perfect compensation. A rapid application is obtained due to the high velocity of air.
The new Westinghouse brake, with storage at 450 lb. per sq. in., permits the use of a small air bottle, also application cylinders of such moderate weight and dimensions that they can be more easily fitted to the vehicle, than was the case with those operating at the lower pressures.
A two-stage compressor is provided, this being designed so that it can be mounted on the engine block, or, in the case of a trolley-bus, direct coupled to a small motor. The cylinder for the first stage of compression delivers air to a special inter-cooler with an amply finned radiating pipe so that the air is cooled before being further compressed in the second-stage cylinder, which brings the pressure up to 450 lb.
For a maximum-load four-wheeler, the reservoir need have a capacity of only about one-tenth cubic ft., so that its dimensions are reduced to a length of, say, 20 ins, and a diameter of 31 ins. It is, of course, provided with a drain plug for condensed water.
The application cylinders are of small bore and comparatively long stroke, and are attached to the axle assemblies in the normal way, the piston rod acting directly on the brake cam lever. The volume of air used is so small that it seems hardly necessary to provide any adjustment for the wear of brake-shoe facings, but, in order to conserve the air used, a simple adjustment is employed. This takes the form of an extensible piston rod, simply designed, and the adjustment is effected by hand-turning a self-locking collar.
In a test of the exhibition set, we found that, with the compressor out of action and the reservoir registering 400 lb., five applications of the four brake cylinders, with a pressure of 100 lb., reduced the reservoir pressure to 300 lb.; 11 applications (i.e., six additional applications) reduced the storage pressure to 200 lb., and 18 applications in all reduced it to 100 lb. Should the compressor, for any reason (such as the stopping of the engine), fail, therefore, an ample safety margin is provided.
Another point, of course, is that the employment of such high pressure means that any small air leakage in a pipe or union would scarcely affect the efficiency of the brake, although it could not be overlooked by the driver, because the dial would show the reservoir not to be holding pressure.
The application valve, simple yet ingenious, works in such a way that the harder the driver presses the pedal, the stronger is the brake application.