Controllable pitch propeller hydraulic locking device

Claim 1

A PROPELLER COMPRISING A HUB AND ANGULARLY ADJUSTABLE PROPELLER BLADES JOURNALLED THEREIN, A PISTON AND CYLINDER IN SAID HUB, A PAIR OF HYDRAULIC LINES OPENING INTO THE TWO ENDS OF THE CYLINDER FOR USE IN ESTABLISHING A PRESSURE DIFFERENTIAL ACROSS THE PISTON FOR FORCING THE PISTON TO SELECTED POSITIONS BETWEEN THE ENDS OF THE CYLINDER, MEANS LINKING SAID PISTON AND CYLINDER WITH THE PROPELLER BLADES TO ANGULARLY ORIENT THE PROPELLER BLADES IN THE HUB AS A FUNCTION OF THE POSITION OF THE PISTON IN THE CYLINDER, A PAIR OF VALVE MEANS MOVABLE ALONG PATHS INTERSECTING SAID HYDRAULIC LINES RESPECTIVELY, AND SPRING-BIASED TO NORMALLY BLOCK THE HYDRAULIC LINES, A HYDRAULIC PRESSURE CONDUIT, A HYDRAULIC RETURN CONDUIT, ANOTHER HYDRAULIC LINE PROVIDING CONTINUOUS FLUID COMMUNICATION BETWEEN THE HYDRAULIC PRESSURE CONDUIT AND BOTH VALVE MEANS TO TRANSMIT CONTINUOUSLY HYDRAULIC PRESSURE IN THE HYDRAULIC PRESSURE CONDUIT TO THE VALVE MEANS IN OPPOSITION TO THE SPRIMNG BIAS, AND CONTROL MEANS SELECTIVELY OPERABLE EITHER FOR BLOCKING THE HYDRAULIC LINES OPENING INTO THE ENDS OF CYLINDER OR FOR PROVIDING FLUID COMMUNICATION BETWEEN THE HYDRAULIC PRESSURE CONDUIT AND EITHER SIDE OF SAID PISTON AND CONCURRENTLY PROVIDING FLUID COMMUNICATION BETWEEN THE FLUID RETURN CONDUIT AND THE OTHER SIDE OF SAID PISTON, WHEREBY SAID BLADES ARE LOCKED RELATIVE TO SAID HUB WHENEVER THERE IS INSUFFICIENT HYDRAULIC PRESSURE TO FORCE AND HOLD SAID VALVE MEANS IN UNBLOCKING POSITION.