| 摘要 |
The present invention provides a pressure relief valve having a broad range of variable relief pressures. The valve has an inlet passage, an outlet passage, a valve seat interposed between said passages, a valving member mounted for movement into and out of sealing engagement with the valve seat, a valve stem assembly operably connected to said valving member, and two or more resilient compression springs of preferably variable length mounted relative to said valve stem to exert a progressively greater compressive force upon said valve stem upon compression of said valve springs, and an adjustable pressure plate assembly for pre-compressing of the compression springs so as to set the relief pressure at a desired pressure value. A preferred embodiment is directed to that comprising a valve stem assembly for preventing the valve spring from being compressed beyond a predetermined selected point of relief pressure. Another preferred embodiment provides a sear assembly which eliminates the possibility of an initial pop-off chattering of the valving member relative to the valve seat. The sear cooperates with the valve base plate to hold the valving member in the sealed position over a pressure span. Once the sear is overcome, valve opening is full. The hysterisis error is thus a desireable value when inspecting a cycle of valve opening and closure.
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