GB1290516A - - Google Patents

Abstract

1290516 Fluid-pressure servomotor systems NORDISK VENTILATOR CO A S 19 Nov 1969 [22 Nov 1968 8 May 1969] 56723/69 Heading G3P [Also in Division F1] An hydraulic actuating system for angularly adjusting the impeller blades 5, Fig. 1 of a single or multi-stage fan, comprises relatively movable working cylinder 12, Figs. 1 and 6, and piston 26. In the Fig. 6 embodiment the piston 26 is fixed to the fan drive-shaft and the cylinder 12 is axially movable and is connected to blade adjusting member 7. The piston may instead be fixed to fanwheel cover 13. Alternatively the cylinder may be fixed thereto or to the fan driver shaft, the piston then being axially movable and connected to the member 7. Pressurized actuating liquid is supplied from a tank 18 by a pump through conduits 17, 33, 35 and 36 into one end of the cylinder 12, from where it passes through a restricted passage 38 in the piston 26 to a lower pressure end of the cylinder 12 and thereafter returns to the tank via conduit 39, metering opening formed by overlapping grooves 40, 41, and conduits 42, 21. In Fig.6 the cylinder is shown in its equilibrium position in which the axial forces produced by the different pressures and areas at the ends of the cylinder are balanced. Axial movement of the cylinder 12 is effected by axially moving a spool 30 within cylinder 29 by means of a rod 15, to increase or decrease the metering opening. The resulting change in the pressure differential across the piston 26 causes the cylinder 12 and attached cylinder 29 to move in the appropriate direction to a new equilibrium position. An optional passage 60 and associated groove 61 communicate the conduit 35 with the lower pressure end of the cylinder 12 when the spool 30 is moved leftwards of the equilibrium position, to thereby assist in transferring liquid from the high to the low-pressure end of the cylinder 12 and thus increase the speed at which the cylinder 12 moves leftwards to its new equilibrium position. The groove 61 may be so placed relative to groove 34 that the spool has to move a small distance from the equilibrium position before the conduit 35 is communicated via groove 61 with the lowpressure end of cylinder 12, or it may be arranged to slightly overlap the groove 34 in the equilibrium position thereby allowing increased throttling at passage 38 and consequent faster rightward movement of the cylinder 12. Leakage accumulating in chamber 70 and in groove 48 is collected via conduits 42, 49.