Pressure metering unit - especially for two stage load dependent railway vehicle brake, has load dependent piston to change from first to second brake stage

摘要

The unit consists of a large piston (25) supported by the vehicle's suspension spring, partially surrounding a housing (10) fixed to the vehicle's chassis. The housing contains two chambers (11, 12) connected by a boring (15) which is regulated by a valve (17) actuated by a spring loaded small piston (23) via a hollow push rod (20) which carries a flange (21) to support the piston return spring (22) and hold the valve (17) on its seat (16). This valve controls the air intake (13) from an auxiliary air tank, the second chamber (12) is connected via a boring (14) with the brake cylinder. A viscous flexible transfer medium (26) is provided between the small piston (23) and the large surrounding piston (25) which becomes compressed as the vehicle load increases until at a predetermined value, the small piston overcomes its spring pressure to lift the valve off its seat to permit the second brake stage to operate.