An hydraulic actuator comprises a first piston and a second piston both working in a bore in a housing and the actuator incorporates a pressure proportioning valve. The valve comprises a valve head for engagement with a seating, first and second stems projecting from the head and through the first piston in each of two opposite directions, each stem being of an area smaller than that of the head, a seal between the first stem and the first piston, a first spring acting between an abutment adjacent to the seal and a shoulder on the first stem to urge the head in a first direction away from the seating and into engagement with a stop, and a second spring acting on an enlargement on the second stem also to urge the head in the first direction and to augment the force in the first spring. The second piston is provided with a longitudinally extending recess into which the second stem and the second spring both project.