Abstract: A double-acting actuating device (1) has a cylinder (2) with a piston (3) connected to a rod (4). The cylinder is provided with ports (8, 9) at opposite ends for flow/return lines (10, 11) to provide flow of hydraulic liquid to whichever side of the piston is to be pressurised for its movement and to provide return of hydraulic liquid from the other side. The lines (10, 11) pass to opposite ends of a shuttle valve (20) having a body (21) with a bore (22) accommodating a double acting piston (23) having short rods (24, 25) extending on either side. Each rod carries a centring spring (26, 27) acting against its face of the shuttle piston and an end fitting (28, 29) of the body. The springs are relatively stiff and centralise the shuttle. The fittings seal the bore, except that each has a central drilling (30) which can freely accommodate the rod on its side of the piston and allow hydraulic liquid flow at the same time.