Locking cylinder with improved locking structure

Claim 1

In a locking cylinder having a main piston slidable in a cylinder and locking means for mechanically locking said piston with respect to said cylinder, the improvement comprising, means defining a keeper on said main piston, said keeper projecting axially from the surface of said main piston and being mounted thereto by means permitting the keeper to shift radially, a latch engageable with said keeper at a predetermined locking position of said keeper and main piston to lock said keeper and main piston in said predetermined position, by restraining movement of said keeper therefrom, means mounting said latch for slidable movement angularly toward and away from said keeper for engagement of said latch therewith at said predetermined position, a latch piston connected to said latch to move the latch away from said keeper in response to an unlatching pressure thereon, means biasing said latch piston radially toward said predetermined position, a passage for applying pressure fluid from a source to said latch piston to move the latch away from said predetermined position, a port through which pressure fluid from said source must flow to act on the full area of said main piston, a blocking piston mounted to said main piston, said blocking piston having a crosswise area which is substantially less than the full area of the main piston; said crosswise area exposed to pressure fluid from said source which tends to move said main piston away from said predetermined position, said blocking piston cooperating with said port when said latch is engaged with said keeper to close said port to flow therethrough, the application of pressure to the full area of the main piston being blocked until said latch has been disengaged from said keeper and said main piston has moved away from said predetermined position sufficiently that said blocking piston no longer closes said port, said latch having an inclined cam surface which bears on a cooperating inclined cam surface provided on said keeper in said locking position, the cam surfaces being such that the unlocking camming force applied by said keeper to said latch when engaged therewith is insufficient to overcome the opposed frictional and biasing forces that restrain cammed movement of said latch, but sufficient in combination with the force of said pressure fluid on said latch piston to move said latch piston and latch radially away from said keeper.