GB1461135A - Apparatus having an actuator cylinder and piston and control valve therefor - Google Patents

Abstract

1461135 Fluid-pressure servomotor systems TEXTRON Inc 11 Oct 1974 [16 Nov 1973] 44175/74 Heading G3P Tandem pistons 30, 32 operating a swash-plate control 16 for a helicopter are controlled by spool valves 220, 222 mounted in sleeves 192 which are displaced against springs 201, 212, if the spools jam. If either one of the spools jams in either a neutral or an off-centre position the corresponding sleeve is displaced to provide a by-pass connection between the two sides of the affected piston, while if both spools jam, direct mechanical actuation takes place from a lever 14. Each spool is supplied through a check-valve 72 from an inlet 66 fitted with a filter 68 and is connected to a return line 124 through a valve 96 opened by the pressure in the supply line 70. A pressure relief valve 128 is also provided. If the spool jams in its neutral position, the sleeve movement opens a by-pass through a check-valve 110 when the sleeve is moved to the right and through a check-valve 112 when the sleeve is moved to the left. If the spool becomes stuck in an off-centre position a by-pass for the affected piston is provided through the passages of the spool and sleeve. The pistons cause the valve body to move and restore the spools to their neutral position, thus providing follow-up control. In a second embodiment, the inlet and return passages terminate at the right hand side of the valve body, the supply check-valves (334), Fig. 13 (not shown) are of simpler construction and the pressure relief valves (360) include a loose-ball closure.