1. A FLUID PRESSURE SERVOMOTOR COMPRISING: A BODY MEMBER HAVING AN AXIALLY EXTENDING POWER CHAMBER THEREIN, A MOVABLE WALL IN SAID POWER CHAMBER CONSTRUCTED AND ARRANGED TO BE DRIVEN TOWARD ONE END OF SAID BODY MEMBER, SAID BODY MEMBER ALSO HAVING A GENERALLY AXIALLY EXTENDING VALVE CHAMBER ADJACENT THE OTHER END THEREOF WHICH VALVE CHAMBER OPENS INTO AND IS GENERALLY CONCENTRIC WITH SAID POWER CHAMBER, A VALVE SLEEVE IN SLIDING ENGAGEMENT WITH THE SIDEWALLS OF SAID VALVE CHAMBER AND CAPABLE OF MOVING INTO ABUTMENT WITH SAID MOVABLE WALL, ABUTMENT MEANS LIMITING MOVEMENT OF SAID VALVE SLEEVE AWAY FROM SAID MOVABLE WALL, A VALVE SPOOL IN THE CENTRAL CHAMBER OF SAID VALVE SLEEVE, INLET MEANS FOR SAID BODY MEMBER PROVIDING FLUID PRESSURE COMMUNICATION WITHIN SAID BODY MEMBER, OUTLET MEANS FOR FLUID PRESSURE FROM SAID BODY MEMBER, SAID VALVE SLEEVE AND VALVE SPOOL CONSTITUTING A COACTING VALVE STRUCTURE WHICH COMMUNICATES SAID OUTLET MEANS TO THE PORTION OF SAID BODY MEMBER LOCATED BETWEEN SAID SLEEVE AND SAID MOVABLE WALL WHEN SAID VALVE SPOOL IS IN A NORMAL POSITION IN SAID SLEEVE AND TO COMMUNICATE SAID INLET MEANS TO SAID PORTION OF SAID BODY MEMBER LOCATED BETWEEN SAID SLEEVE AND SAID MOVABLE WALL WHEN SAID VALVE SPOOL IS MOVED TO AN ACTUATING POSITION IN SAID SLEEVE LOCATED IN THE DIRECTION OF SAID MOVABLE WALL FROM SAID NORMAL POSITION, MEANS FOR BIASING SAID VALVE SPOOL TOWARD ITS NORMAL POSITION, AND ACTUATING MEANS PROJECTING OUT OF SAID SLEEVE FOR MOVING SAID VALVE SPOOL, SAID ACTUATING MEANS INCLUDING A LOST MOTION CONNECTION FOR DRIVING SAID VALVE SLEEVE INTO ENGAGEMENT WITH SAID MOVABLE WALL, AND SAID LOST MOTION CONNECTION BEING GREATER IN LENGTH THAN THE MOVEMENT OF SAID SPOOL FROM ITS NORMAL TO ITS ACTUATING POSITON; SAID MEANS FOR BIASING SAID VALVE SPOOL BEING EFFECTIVE TO RETAIN SAID SLEEVE AGAINST ITS ABUTMENT DURING POWER ACTUATION OF THE MOVABLE WALL DURING ACTUATION OF SAID VALVE SPOOL THROUGH SAID LOST MOTION CONNECTION AND FURTHER MOVEMENT OF SAID ACTUATING MEANS EFFECTING ABUTMENT OF SAID SLEEVE WITH SAID MOVABLE WALL TO OBTAIN DISPLACEMENT OF SAID MOVABLE WALL UNDER POWER FAILURE.