C.D. Pioneered
Page 53
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Vacuum Brakes
SO far as can be traced, the late J. G. Parry Thomas, one-time holder of the land-speed record, was the first man to have practical ideas on the use of the vacuum existing in the induction' system of a petrol engine to supplement the effort applied by the driver to operate the brakes.
This interesting information was given by Mr. S. H. Edge, M.I.Mech.E., chief engineer and assistant general manager of Clayton Dewandre Co., Ltd., when he read a paper dealing with vacuum and air-pressure braking before members of the Institute of Road Transport Engineers in London, yesterday.
The Thomas patent was taken out in November; 1919, and was regarded as a master patent. It had been stated that, because of its existence, the development of vacuum-servo systems in America were not on the lines of British and Continental systems. M. Dewandre and through him, Clayton Dewandre, owned this patent until it expired. Except for detail refinements, the original Dewandre rnonobloc servo, introduced in 1925, remained unchanged to•this day. Probably the greatest factor in the early development of vacuum brakes, said Mr. Edge, was the Dewandre lever motion, which enabled the power of the vacuum cylinder to be precisely controlled in relation to the effort exerted on the brake pedal.
Air-pressure braking equipment was first produced by the Clayton Pewandre concern in 1932, the first layout being similar in general form to the modern vacuum triple system.
• In the pm-war years there was no great demand for air-pressure braking • although several. prototype vehicles had it. In 1938, the company was approached by, London Transport to assist in the development of an airpressure system which was to be used for braking and gear changing.
. Since 1945, interest in air-pressure systems had increased and several specialized designs were now in production.