Fail safe apparatus for fluid actuated systems

Claim 2

A fluid pressure cutoff apparatus comprising a housing, a bore extending from one end of said housing to the other end, a spool slidably mounted in said bore for movement axially of said bore between a central position and side positions, said bore having annular shoulders spaced from the eNds of said bore forming end chambers and supporting said spool, centering means for resiliently holding said spool in a centered position, fluid supply passages connected to said end chambers for communicating with separate valve means, said spool having ends extending into said end chambers and having the same effective end areas subjected to fluid pressure whereby said spool is biased from a central position to one of said side positions when the fluid pressure in one of said end chambers exceeds the fluid pressure in the other of said end chambers by a force exceeding the resilient force of said centering means, said spool having annular lands in sealing engagement with said bore at positions between said annular shoulders dividing the space between said spool and said bore into a central chamber and side chambers, a central inlet passage in communication with said bore for admitting fluid into said central chamber and a central outlet passage for communicating fluid out of said central chamber with said spool in said central position and for cutting off communication of said fluid out of said central chamber when said spool is displaced into one of said side positions, side inlet passages located in communication with said bore between said annular shoulders and said central inlet passage for communicating fluid under pressure into one of said side chambers when said spool is in a side position whereby fluid pressure acts against the effective area of one of said annular lands of said spool to supplement the force on said spool ends biasing said spool and locking said spool in the side position.

Claim 3

A fluid pressure cutoff apparatus according to claim 1 wherein said centering means includes annular rings disposed in said end chambers having flanges engageable with said annular shoulders and overlapping the ends of said spool and compression springs disposed in said end chambers with one end of each of said springs engaging the end of said housing and the other end of said springs engaging one of said annular rings to resist movement of the spool from a centered position and limit the movement of said springs.

Claim 4

A fluid pressure cutoff apparatus according to claim 1 wherein each of said end chambers has an axially extending post and said ends of said spool have recesses for receiving said posts when said spool is moved into one of said side positions whereby the effective end area subjected to fluid pressure in said end chambers is reduced to further lock said spool in the side position.

Claim 5

A fluid pressure cutoff apparatus according to claim 3 wherein said centering means includes annular rings having flanges engageable with said annular shoulders and overlapping the ends of said spool and compression springs disposed in said end chambers with one end of each of said springs engaging the end of said casing and the other ends of said springs engaging one of said slidable annular rings to resist movement of the spool from a centered position and limit the movement of said springs.

Claim 6

A fluid pressure cutoff apparatus according to claim 1 wherein said separate valve means includes a pair of position sensor valves in communication with a common fluid pressure source, each of said position sensor valves having a fluid passage for communicating fluid pressure to one of said end chambers, each of said position sensor valves having an exhaust passage and slidable valve means for communicating fluid pressure to one of said end chambers in response to the positioning of said valve means.

Claim 7

A fluid pressure cutoff apparatus comprising a housing, a bore extending from one end of said housing to the other end, a spool slidably mounted in said bore for movement axially of said bore between a central position and side positions, said bore having end chambers, centering means for resiliently holding said spool in a centered position, fluid supply passages in communication with said end chambers for communicating fluid pressure from separate position sensor valves, said spool hAving ends extending into said end chambers and having the same effective end areas subjected to fluid pressure, said spool having annular lands in sealing engagement with said bore at positions between said end chambers dividing the space between said spool and said bore into a central chamber and side chambers, a central inlet passage in communication with said housing for communicating fluid under pressure into said central chamber and a central outlet passage in communication with said central chamber for communicating fluid under pressure out of said central chamber with said spool in a central position and for cutting off communication of said fluid under pressure out of said central chamber when said spool is displaced into one of said side positions, each of said position sensor valves having an inlet passage in communication with a common fluid pressure source and an outlet passage in communication with one of said end chambers, said pressure sensor valves having exhaust passages and valve means for communicating fluid under pressure to said end chambers in one position of said valve means and exhausting fluid from said end chambers in another position of said valve means whereby the pressure in said end chambers is maintained equally when said valve members of said pressure sensor valves are in the same relative positions and the pressure in one of said end chambers is greater than the pressure in the other of said end chambers when the valve member of one of said pressure sensor valves is in a different position from the valve member of the other of said pressure sensor valves.

Claim 8

A fluid pressure cutoff apparatus comprising a housing, a bore extending from one end of said housing to the other end, a spool slidably mounted in said bore for movement axially of said bore between a central position and side positions, said bore having end chambers, centering means for resiliently holding said spool in a centered position, fluid supply passages in communication with said end chambers for communicating fluid pressure from separate position sensor valves, said spool hAving ends extending into said end chambers and having the same effective end areas subjected to fluid pressure, said spool having annular lands in sealing engagement with said bore at positions between said end chambers dividing the space between said spool and said bore into a central chamber and side chambers, a central inlet passage in communication with said housing for communicating fluid under pressure into said central chamber and a central outlet passage in communication with said central chamber for communicating fluid under pressure out of said central chamber with said spool in a central position and for cutting off communication of said fluid under pressure out of said central chamber when said spool is displaced into one of said side positions, each of said position sensor valves having an inlet passage in communication with a common fluid pressure source and an outlet passage in communication with one of said end chambers, said pressure sensor valves having exhaust passages and valve means for communicating fluid under pressure to said end chambers in one position of said valve means and exhausting fluid from said end chambers in another position of said valve means whereby the pressure in said end chambers is maintained equally when said valve members of said pressure sensor valves are in the same relative positions and the pressure in one of said end chambers is greater than the pressure in the other of said end chambers when the valve member of one of said pressure sensor valves is in a different position from the valve member of the other of said pressure sensor valves.

Claim 9

A fluid pressure cutoff apparatus according to claim 6 wherein said valve members of said position sensor valves have lands located in positions for closing said exhaust passages and with said inlet passages and outlet passages being in communication to communicate fluid pressure to said end chambers in the normal condition of said cutoff apparatus.

Claim 10

A fluid pressure cutoff apparatus according to claim 6 wherein said valve members of said position sensor valves have lands located in positions for closing said inlet passages and with said outlet passages and said exhaust passages being in communication to communicate fluid pressure to said end chambers in the normal condition of said cutoff apparatus.

Claim 11

A fluid pressure cutoff apparatus according to claim 6 wherein said valve members of said position sensor valves have lands for opening and closing said inlet passages, outlet passages and exhaust passages, said lands of one of said valve members being offset from the lands of the other of said valve members for controlling the communication of fluid pressure to said end chambers to maintain said spool in a centered position where one of said valve members normally moves before the other of said valve members and it is necessary to compensate for this advance movement.

Claim 12

A fluid pressure cutoff apparatus according to claim 6 wherein said valve members of said position sensor valves have lands for controlling the communication of fluid pressure between said inlet passages, outlet passages and exhaust passages, the positioning of said lands relative to the positions of said passages in communication with one of said position sensor valves being different from the positioning of said lands relative to the positions of said passages in communication with the other of said position sensor valves to provide for controlling the communication of fluid pressure to said end chambers to maintain said spool in a centered position where one of said valve members normally moves before the other of said valve members and it is necessary to compensate for this advance movement.

Claim 13

A fluid pressure cutoff apparatus according to claim 6 wherein said valve members of said position sensor valves have lands for controlling the communication of fluid pressure between said inlet passages, outlet passages and exhaust passages, said passages of one of said position sensor valves being offset fRom said passages of the other of said position sensor valves for controlling the communication of fluid pressure to said end chambers to maintain said spool in a centered position where one of said valve members normally moves before the other of said valve members and it is necessary to compensate for this advance movement.