Hydraulic control means for check valves

Claim 1

In a check valve of the clapper type installed in a high pressure gas pipeline including a hinged clapper, the improvement comprising means to control the slamming of said clapper against its seats on reversal of flow, comprising: a. a chambered cylindrical hydraulic apparatus having in a central chamber a cylinder having hydraulic liquid therein, a piston slidably and sealably received in said cylinder; b. a first piston rod attached to said piston on a first side and sealed through a first header on a first end of said cylinder, said first piston rod extending into a first gas chamber; c. said first gas chamber attached at its first end to said first header and at its second end to the housing of said valve, said first gas chamber exposed to the gas pressure in said valve, slider means in said first gas chamber attached to said first piston rod; d. connecting rod means rotatably connected to said clapper and to said slider; e. second piston rod means attached to the second side of said piston and sealed through a second header on the second end of said cylinder, said second piston rod extending into a second gas chamber; f. said first and second piston rods having substantially equal cross sectional areas opened to the pressure in the respective gas chambers; g. said second gas chamber comprising a sealed chamber attached to said second header; h. bypass means extending between the first and second gas chambers for equalizing the pressures therein with the gas pressure in the valve; and i. valved passageway means providing communication between the opposite sides of the piston for controlling the flow of hydraulic liquid from one side of said piston to the other and allowing substantially unrestricted liquid flow in an opposite direction.