Variable tensioning system for shear seal valves

An instrumentation valve comprising:

• (a) a first housing comprising a valve body having a first fluid flow passage therethrough cooperatively arranged relative to a valve seat;
• (b) a valve element adapted to be seated against said valve seat and having first and second operative positions, one position opening said first fluid flow passage through said valve body for fluid flow and the other position closing said first fluid flow passage against fluid flow, said first housing enclosing said valve element therein against said valve seat;
• (c) a second housing joined to said first housing, said second housing having a second fluid flow passage therethrough operatively connected with said first fluid flow passage;
• (d) valve element bias means providing a relatively fixed force, said bias means bearing against said valve element to relatively urge said valve element into sealing engagement with said valve seat to enable fluid flow up to a minimum pressure to flow through said first fluid flow passage and past said valve seat without leakage;
• (e) fluid pressure responsive means in said second housing cooperatively arranged relative to said second fluid flow passage including a fluid pressure receiving chamber means adapted to be connected to the source of fluid to be switched by the valve, said chamber means further including coupling means extending from said chamber means to said valve element to provide a variable force to said valve element responsive to fluid pressure in said second fluid flow passage to variably load said valve element as a function of the pressure of the fluid to be switched;
• and
• (f) said first and second fluid flow passages being cooperatively connected to permit fluid to flow from the source of fluid to be switched through the second fluid flow passage in said second housing and then through said first fluid flow passage in said first housing.