Abstract: A pressure-operated linear actuator in which the working liquid is Electro-Rheological (ER) fluid in which there is a single flow path between an inlet and an outlet of an associated pump in which there are two or more pistons and fluid chambers delineated by these pistons, which fluid chambers are connected in series by stationary ER valves distinct from the pistons such that the pressure as determined by each of the ER valves is applied to one or more of the chamber(s), wherein one or both of the ER valves are divided into two or more sections in order to minimize the length, and maximize the cross-sectional area, of the inactive connecting passages.

Abstract: A variable discharge pump (3) comprises a piston (4) reciprocable within a cylinder (2), a displaceable inlet valve (5) adapted to control admission of lower pressure hydraulic fluid (9) to the swept volume areal (10) of the piston (4) and cylinder (2), a displaceable outlet valve (7) adapted to control delivery of higher pressure fluid (9) from the swept volume area (10), and means (13, 13A, 26-28, 29-44) to control the position of the inlet valve (5) so as to control the volume of fluid (9) delivered by the pump (3) in accordance with demand.

Abstract: A variable displacement pump (3) comprises a piston (4) reciprocable within a cylinder (2), a displaceable inlet valve (5) adapted to control admission of lower pressure hydraulic fluid (9) to the swept volume area (10) of the piston (4) and cylinder (2), a displaceable outlet valve (7) adapted to control delivery of higher pressure fluid (9) from the swept volume area (10), and means (13, 13A, 26-28, 29-44) to control the position of the inlet valve (5) so as to control the volume of fluid (9) delivered by the pump (3) in accordance with demand.

Abstract: An electro-rheological fluid comprising a hydrophilic solid and a hydrophobic liquid component wherein the hydrophobic liquid component comprises a fluorosilicone whose average molecular weight is in the range 200-700.

Abstract: An electrically controlled, progressive, frictional, torque transmitting device comprises a rotary element 1, 2, a proportion of the rotary power available from the rotary element 1, 2, being used, under the control of a direct electrical signal, to determine the degree of engagement of a frictional device 3, and hence the torque transmitted or absorbed by the torque transmitting device, thereby avoiding the requirement for an additional power source to activate the frictional device whole.