JPS6256525B

PURPOSE:To keep the secondary pressure constant, by providing a check control valve and a secondary pressure operation control valve respectively in flow paths sectioned. CONSTITUTION:A check control valve 4 consisting of a main valve 2 and a pilot valve 3 is inserted in a flow path 1, and a secondary pressure actuated control valve 5 is inserted in a flow path 27. Further, the secondary pressure chamber 6 of the valve 3 is connected to the secondary side of the main valve 2 through a pipe path 7. Further, at operation, the main valve 2 is driven with a driving pressure from the pilot valve 3, and the opening between a valve body 25 and a valve hole 26 is made greater with the secondary pressure decreased and the driving pressure increased. On the other hand, when the secondary pressure is increased in the control valve 5, a diaphragm 28 is displaced, a valve body 32 approaches a valve hole 33, the opening is made smaller, and if the secondary pressure is decreased, the opposite operation is made, resulting that the secondary pressure is kept constant.