1. IN A FLUID PRESSURE SERVOMOTOR HAVING A HOUSING DIVIDED INTO TWO COMPARTMENTS BY A POWER PISTON, A CONTROL VALVE FOR CONTROLLING THE OPERATION OF THE SERVOMOTOR, SAID CONTROL VALVE COMPRISING A CASING, A FIRST CHAMBER IN SAID CASING CONNECTED TO ONE OF THE COMPARTMENTS AND TO A FIRST SOURCE OF FLUID PRESSURE, A SECOND CHAMBER CONNECTED TO THE OTHER OF THE COMPARTMENTS, SAID FIRST AND SECOND CHAMBERS BEING SEPARATED BY A FLUID PRESSURE RESPONSIVE MEMBER OPERATIVELY CONNECTED TO A VALVE ACTUATING MEMBER, A THIRD CHAMBER CONNECTED TO A SECOND SOURCE OF FLUID PRESSURE DELIVERING FLUID AT A PRESSURE DIFFERING FROM THAT OF THE FIRST SOURCE AND A MOVABLE VALVE ASSEMBLY FORMED O A FIRST VALVE MEMBER CONTROLLING THE