Load-responsive Braking
Page 70
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A POWER-BRAKING scheme for 1-1 trailers in which the maximum operating force is controlled by the load carried is shown in patent No. 889,804. (Clayton Dewandre Co., Ltd., Titanic Works, Lincoln.)
The drawing shows an outline of the set-up as applied to a trailer. The vacuum or air pressure line (1) passes through a control valve (2) on its way to the cylinder (3) that applies the brakes.
The control valve is the unit that adjusts the brake effort to the load. It is operated by a lever (4) coupled to the axle. The action of the lever, under increasing load, is to increase the loading on the spring of the control valve. The spring is arranged to resist the closing of the valve which is of the diaphragm type and designed so that the vacuum or air pressure supply from the tractor also tends to shut off the supply to the trailer brakes.
Under light load, the spring is only slightly compressed, so that the control valve allows only a limited supply of vacuum or air pressure to reach the brakes. With additional load this is increased until maximum braking is available with full load.