GB737745A - Improvements in or relating to hydraulically operated variable pitch propellers - Google Patents

Abstract

737,745. Variable-pitch propellers. ROTOL, Ltd. June 5, 1953 [May 8, 1952], No. 11670/52. Class 114. In a hydraulically operated variable pitch propeller in which liquid is supplied through a coarse pitch conduit 47, 95 to a pitch change motor to increase the pitch of the blades, a normally open lock valve 52 in the conduit is closed in response to the attainment of a propeller speed in excess of a predetermined value, the 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 (95) of the valve above that on the other side (47), and a non-return valve 53 is provided in a conduit bypassing the lock valve and arranged to be closed when the pressure on the pitch change motor side (95) exceeds that on the other side (47). The valve 52 is tubular and closes an orifice 51 under the control of fly-weights 62, the opposite end is of large diameter and slides in a cylinder 59 so that when the valve closes it is held closed by the pressure acting on that end. The non- return valve is mounted in the end of the cylinder 59. The propeller is reversible and is provided with a fine pitch stop and a super-fine pitch stop or in a modification is non-reversible and is provided with a fine pitch stop. Liquid to feather the blades is supplied by a conduit 48 and passes to the motor via a duct 87. Increased pressure to release the fine pitch stop and put the blades into super-fine pitch opens a valve 45 and allows liquid to pass to the stop release device. Still higher pressure passes through the valve 45 to release the super-fine pitch stop when the propeller is to be reversed. To prevent the valve 52 closing during momentary over speeding while the blades are passing to super-fine or reverse pitch, an overriding device is provided to hold the valve 52 open. This device comprises a cylinder supplied with liquid through a valve 69, arranged to open at a predetermined pressure, containing a piston 49 which moves out to contact a rod 66 secured to the valve 52. In a modification the piston carries a rod which contacts the valve 52 and the under side of the piston is vented to the other side (47) of the valve 52. Specification 672,953, [Group XXXII], is referred to. Reference has been directed by the Comptroller to Specification 691,755.