Variable Braking for Trailers hiE011. 1 A1 PRESSURE 57 P.5
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A MANUAL control giving high-, mediumand low-pressure braking for trailers has been produced by the Clayton Dewandre Co., Ltd., Lincoln. It can be employed in any type of airpressure braking system. It is known as the light-laden valve and may be fitted in single-line, two-pipe-line and inverted-line systems.
The control unit acts as a pressurereducing valve and is used to restrict the maximum pressure in the brake line to 28 p.s.i. when the trailer is travelling without a load and to 57 p.s.i. for partial-load operations. In the third position, full pressure is applied to the brake line.
The valve lever actuates a three-faced cam which pre-loads a coil spring acting on a reaction piston. This is in contact with an extension of a spring-loaded inlet valve, and when the lever is in the high-pressure position-the load on the spring is sufficient .to .keep the valve open. Maximum pressure is then relayed to the trailer brakes.
Movement of the lever to the central position relieves the spring pressure on the reaction piston and the inlet pressure tends to close the valve, thus
reducing the pressure acting on the trailer brakes.
In the third position of the lever the cam lift is at a minimum and the lower reaction force of the piston further reduces the trailer line pressure.
When used in a single-line system the valve is fitted behind the coupling. If the system is of the two-pipeline type it is located in the service line between the coupling and the relay emergency salve. in an inverted system it is installed between the control valve and the brake cylinders or chambers.