Hydraulically operated variable pitch propellers

Claim 1

IN A HYDRAULICALLY OPERATED VARIABLE PITCH PROPELLER COMPRISING A PLURALITY OF PROPELLER BLADES, A HYDRAULIC PITCH CHANGE MOTOR OPERATIVELY CONNECTED TO ADJUST THE PITCH OF THE BLADES, AND A COARSE PITCH FLUID CONDUIT CONNECTED TO SAID MOTOR TO CONVEY HYDRAULIC FLUID THERETO TO ACTUATE THE MOTOR IN THE SENSE TO INCREASE THE PITCH OF THE BLADES, A NORMALLY OPEN LOCK VALVE IN SAID COARSE PITCH CONDUIT, PROPELLER SPEED RESPONSIVE MEANS OPERATIVELY CONNECTED WITH SAID LOCK VALVE FOR CLOSING THE LOCK VALVE SOLELY IN RESPONSE TO THE ATTAINMENT OF A PROPELLER SPEED IN EXCESS OF A PREDETERMINED MAXIMUM OPERATING VALUE, SAID LOCK VALVE BEING ADAPTED SO THAT AFTER IT HAS BEEN CLOSED IT REMAINS CLOSED WHEN THERE IS AN EXCESS OF PRESSURE ON THE PITCH CHANGE MOTOR SIDE OF THE LOCK VALVE ABOVE THAT ON THE OTHER SIDE, A BY-PASS FLUID CONDUIT BYPASSING SAID LOCK VALVE, AND A NON-RETURN VALVE IN SAID BY-PASS CONDUIT FOR CLOSING SAID BY-PASS CONDUIT WHEN THE PRESSURE ON THE PITCH CHANGE MOTOR SIDE OF THE NON-RETURN VALVE EXCEEDS THAT ON THE OTHER SIDE OF THE NON-RETURN VALVE.