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A controlled piston (20, 62, 102) having a first end (24, 64, 104) mounted in a controlled piston sleeve (22) and a spool (16) movably mounted in a spool sleeve (18), a first fluid passage (40, 66, 108) from the spool (16) to the controlled piston first end (24, 64, 104), the position of the spool (

A controlled piston (20, 62, 102) having a first end (24, 64, 104) mounted in a controlled piston sleeve (22) and a spool (16) movably mounted in a spool sleeve (18), a first fluid passage (40, 66, 108) from the spool (16) to the controlled piston first end (24, 64, 104), the position of the spool (16) affecting a position of the controlled piston (20, 62, 102), an FFV (42, 68, 110) in an FFV sleeve (44, 70, 112) in the first fluid passage (40, 66, 108) having a first end section (46, 74, 116), a second end section (48, 78, 120) and a central section (50, 82, 126) having a third diameter less than the diameters of the first and second sections, the FFV (42, 68, 110) being shiftable between a first position blocking the first fluid passage (40, 66, 108) and a second position allowing fluid flow past the central section (50, 82, 126) to the controlled piston (20, 62, 102), and a second fluid passage (56, 88, 134) from the spool (16) to the FFV first end section (46, 74, 116). Shifting the spool (16) to a failsafe position shifts the FFV (42, 68, 110) to the first position to fix the controlled piston (20, 62, 102) in place.

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What is claimed is: 1. A system comprising: a controlled piston slidably mounted in a controlled piston sleeve and having a first end; a spool movably mounted in a spool sleeve; a first fluid passage from said spool to said controlled piston first end, the position of said spool affecting the fluid

What is claimed is: 1. A system comprising: a controlled piston slidably mounted in a controlled piston sleeve and having a first end; a spool movably mounted in a spool sleeve; a first fluid passage from said spool to said controlled piston first end, the position of said spool affecting the fluid pressure applied to said controlled piston first end and a position of said controlled piston; an FFV in an FFV sleeve in said first fluid passage having a first end section having a first diameter, a second end section having a second diameter and a central section having a third diameter less than said first and second diameters, said FFV being shiftable between a first position blocking said first fluid passage and a second position allowing fluid flow past said central section to said controlled piston; and a second fluid passage from said spool to said FFV first end section; whereby shifting said spool to a failsafe position shifts said FFV to said FFV first position to seal a fixed volume of fluid between said FFV and said controlled piston first end. 2. The system of claim 1 wherein said second diameter is greater than said first diameter. 3. The system of claim 2 wherein said FFV sleeve has an FFV volume between said FFV first end section and said FFV second end section, said FFV volume when said FFV is in said first position being greater than said FFV volume when said FFV is in said second position. 4. The system of claim 1 wherein said spool comprises a second stage spool of an electrohydraulic servovalve. 5. The system of claim 1 including a spring biasing said FFV toward said second position. 6. The system of claim 1 wherein said controlled piston includes a second end and including a third fluid passage from said spool to said second end. 7. The system of claim 6 wherein said controlled piston includes an annular control surface spaced from said second end and including a fourth fluid passage from said second fluid passage to said annular control surface. 8. The system of claim 1 wherein said FFV includes a longitudinal bore connecting said FFV first end to an opening in a sidewall of said FFV second end section. 9. The system of claim 8 wherein said opening is blocked by said FFV sleeve when said FFV is in said first position. 10. The system of claim 1 including a fifth fluid passage from said spool to said FFV second end. 11. A system comprising: a controlled piston slidably mounted in a controlled piston sleeve and having a first end and a second end; an electrohydraulic servovalve having a second stage spool movably mounted in a spool sleeve; a first fluid passage from said spool to said controlled piston first end, the fluid pressure in said first fluid passage affecting a position of said controlled piston; an FFV in an FFV sleeve in said first fluid passage, said FFV having a first end section having a first diameter, a second end section having a second diameter greater than said first diameter and a central section having a third diameter less than said first and second diameters, said FFV being shiftable between a first position blocking said first fluid passage and a second position allowing fluid flow past said central portion to said controlled piston; a second fluid passage from said spool to said FFV first end section; a third fluid passage from said spool to said controlled piston second end; and a fourth fluid passage from said spool to said FFV second end. 12. The system of claim 11 including a spring biasing said FFV toward said second position. 13. The system of claim 11 wherein said controlled piston includes an annular control surface spaced from said second end and including a fifth fluid passage from said second fluid passage to said annular control surface. 14. The system of claim 11 wherein said FFV includes a longitudinal bore connecting said FFV first end to an opening in a sidewall of said FFV second end section. 15. The system of claim 11 wherein said opening is blocked by said FFV sleeve when said FFV is in said first position. 16. In a system comprising: a controlled piston slidably mounted in a controlled piston sleeve and having a first end; a spool movably mounted in a spool sleeve; a first fluid passage from said spool to said controlled piston first end, an FFV in an FFV sleeve in said first fluid passage, said FFV having a first end section having a first diameter, a second end section having a second diameter and a central section having a third diameter less than said first and second diameters, a method comprising the steps of: shifting said spool to control fluid flow in said first fluid passage to control the position of said controlled piston; and in the event of a power loss when said controlled piston is in a position, shifting said spool to a failsafe position, increasing a fluid flow in said first fluid passage to move said controlled piston from said position, and increasing a volume in said FFV sleeve to compensate for said increased fluid flow and return said controlled piston to said position; and blocking said first fluid passage to maintain said controlled piston in the position.