66 is closed when pressure in the line 52 is increased relative to pressure in the line 50 by downwardly displacing the piston 38 as described above the sleeve will displace downward this downward displacement of the sleeve 70 will cause the closure 66 to open for example by pivoting the member 80 so that it no longer blocks access and flow through the passage 68 when pressure in the line 50 is increased relative to pressure in the line 52 by upwardly displacing the piston 38 as described above the sleeve will displace upward this upward displacement of the sleeve 70 will cause the closure 66 to close for example by allowing the member 80 to pivot across the passage 68 and again block flow and access through the passage a mechanism not shown may be provided for releasably maintaining the sleeve 70 in its upper and or lower position for example a spring or other biasing device could be used to prevent the sleeve 70 from displacing downward due to its own weight when it is desired to keep the valve 28 closed alternatively or in addition a detent mechanism such as a snap ring collet spring loaded detent etc could be used to releasably secure the sleeve 70 in its upper.