Control device for gradually increasing fluid pressure

Claim 1

In a control device for gradually increasing fluid pressure interposed between a pressure generating source And an hydraulic actuator including a valve casing including a fore-pressure chamber which is in fluid communication with said hydraulic actuator, a back-pressure chamber, a drain port and a cylindrical valve in which is fitted a pressure regulator valve for regulating fluid pressure and having radial passages for blowing off pressure fluid, said radial passages being movable in response to an increase of pressure in said back-pressure chamber to cause said pressure regulator to block said radial passages to gradually increase fluid pressure in said actuator, and a quick return valve which is movably mounted between said fore- and back-pressure chambers for movement from a first position in which said quick return valve blocks said fore- from said backpressure chamber and in which said back-pressure chamber is in communication with said drain port to a second position in which said quick return valve allows communication between said chambers and a spring for biassing said quick return valve to said first position, the improvement comprising that said quick return valve is constructed so that is back side is directly connected only with said back-pressure chamber so that when the pressure in said fore-pressure chamber is suddenly reduced the drain port of said back-pressure chamber is slightly opened by the pressure in said back-pressure chamber against the back side of the quick return valve itself thus quickly reducing the pressure in said back-pressure chamber and allowing an urging force due to the fluid pressure inside said fore-pressure chamber acting on one side of said quick return valve to balance with an urging force due to the biassing force of said spring combined with the fluid pressure inside of the back-pressure chamber acting on the back side of said quick return valve whereby the sensitivity of said quick return valve to pressure variations in said fore-pressure chamber is heightened so that when said pressure in said fore-pressure chamber is reduced to a predetermined level, the quick return valve is quickly forced to its first position in which communication between said fore- and back-pressure chambers is cut-off and said quick return valve fully communicates said drain port and said back-pressure chamber whereby said back-pressure chamber''s pressure, and thus the pressure acting upon said cylindrical valve, is quickly reduced.