| 摘要 |
<p>A variable load valve device for modulating brake cylinder pressure on railway freight cars according to the actual vehicle load weight. A load sensing arm detects variations between the sprung and unsprung members of the vehicle to vary the tension of a pair of springs, one of which bias a proportioning valve to a normally closed position and the other of which biases a cut-off valve to a normally open position. The proportioning valve controls fluid pressure communication between the brake cylinder and a volume reservoir, such that when the proportioning valve spring tension is overcome by the brake cylinder pressure, the brake cylinder pressure will be modulated by flowing to the volume reservoir. By reason of the variable spring tension with load, the level of brake pressure at which modulation occurs increases with increased load so that the degree of brake pressure modulation reduces as the load increases. Light brake applications at low load weights may be unmodulated or only slightly modulated, while heavier brake applications are fully modulated. The cut-off valve operates to cut-off supply of pressure (auxiliary reservoir) to the brake cylinder when this pressure reaches a value corresponding to "full equalization" to prevent an overreduction of brake pipe pressure from affecting the modulated brake pressure. Changes in the modulated brake pressure with load variations are compensated by the load adjusted bias spring to assure cut-off at full equalization value regardless of the modulation pressure.</p> |
