Hydraulic jack

A hydraulic jack comprising a cylinder, a piston slidable relative within the cylinder, an inlet in the cylinder, a pump for supply of fluid under pressure to said inlet to move the piston, a seal between the piston and the cylinder, means for limiting the stroke of the piston in the cylinder by permitting fluid pumped into the cylinder, once the piston reaches the end of its permitted stroke, to escape from the cylinder to a zone of relatively low pressure, said stroke limiting means comprising an element carried by one of the piston and the cylinder and urged towards a position in which it engages in a recess or groove in the other of the piston and the cylinder positively to prevent further movement of the piston at said end of said permitted stroke, said stroke limiting means, when so activated, also mechanically preventing removal of the piston from the cylinder, and means for selectively de-activating said stroke limiting means in order to allow said piston to be withdrawn from the cylinder, said de-activating means being a device operable to prevent said element moving into engagement with said recess or groove when the piston reaches said end of said permitted travel.