GB783910A - Improvements in hydraulic variable pitch propellers - Google Patents

Abstract

783,910. Variable pitch propellers. ROTOL, Ltd. May 1, 1956 [May 5. 1955], No. 13106/55. Class 114. A variable pitch propeller of the kind actuated by a double acting hydraulic pitch change motor supplied through coarse and fine pitch conduits comprises a normally open pitch lock valve 5 in the coarse pitch conduit 4, closing means, such as flyweights 7 opposed by a spring 6, for closing the valve when the propeller speed exceeds a predetermined value, a non-return valve 10 in a conduit 9 by-passing the lock valve 5 and arranged to remain closed when the pressure on the motor side of it exceeds that on the other side, and adjusting means for the closing means for adjusting them to close the lock valve when the difference in pressure between that in the fire pressure conduit 3 and that in a drain 16 falls below a predetermined value. The adjusting means consists of a piston 11 in a cylinder 12, one end of which communicates with the fine pitch conduit 3 and the other with the drain 16, the piston having a rod 17 carrying a plate 18 engaging the spring 6 to add to the pressure thereof the above-mentioned differential pressure. If this latter pressure falls below a predetermined value the spring 6 displaces the plate 18 and piston 11 to the left and the flyweights 7 close the lock valve 5. The predetermined value is such that this occurs at a speed about 80 per cent of the normal speed. If the propeller is running at an overspeed, e.g. 8 per cent in excess of that called. for, the flyweights 7 close the lock valve and the motor is supplied through the conduit 9 until reduced speed permits the valve 5 to be opened and coarse pitch fluid to flow normally through it. A second piston 19 and cylinder 21 may be provided to co-operate with the piston 11. The cylinder 21 is connected at one end to the coarse pitch conduit and at the other to drain and the piston rod 20 enages the piston 11, the arrangement evening out transient pressure changes. Specification 737,745 is referred to.