When piston 1 is moved to the right by fluid entering the left end of cylinder 3, balls a, held in a special cage of the piston, are forced outward by bevelled member d of plunger 2 and enter an annular groove of cylinder 3, locking piston 1 in the cylinder (see Fig. a). To open the lock, fluid under pressure is delivered through passage 4 (see Fig. b) into the space between piston 1 and plunger 2. This moves plunger 2 to the right, compressing spring 5 and releasing balls a. Then piston 1 is moved by the fluid to the left.
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