| 摘要 |
PCT No. PCT/US79/00859 Sec. 371 Date Oct. 15, 1979 Sec. 102(e) Date Oct. 15, 1979 PCT Filed Oct. 15, 1979 PCT Pub. No. WO81/01034 PCT Pub. Date Apr. 16, 1981 In prior art hydraulic systems, and in particular in hydraulic systems having a cylinder means for elevating and lowering a load, there exists the possibility that the hydraulic line from a control valve to the cylinder means could rupture, allowing the load to drop before the operator could react. The present invention solves this problem by providing a blocker valve (100) in the vent line (69) of a check valve (33,34) which check valve is interposed in the main line 27 between a cylinder means (12) and a control valve (21). The blocker valve (100) is responsive to the back pressure in the main line (27) from the check valve (33,34) to the control valve (27). Thus, when the pressure in said main line (27) drops below a predetermined level due, for example, to a break in said line (27) the blocker valve (100) automatically closes the vent line (69), preventing the check valve (33,34) from releasing hydraulic fluid, and thus preventing the load (14) from dropping. In an aspect of the invention, a resolver valve (104) actuates the blocker valve (100). The resolver valve (104) communicates with the main line (27) at two positions and selects the lowest pressure between said positions.
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