Fluid-actuated chuck-operating mechanism with a fluid lock

Claim 1

Fluid-operating mechanism for a chuck, comprising an operationally turning cylinder with opposite first and second ends and a piston therein; a swivel coupling having companion parts, of which one coupling part is operationally stationary, and the other coupling part is turnable with said cylinder and has first and second orifices leading to said first and second Cylinder ends, respectively, said one coupling part having first and second apertures in communication with said first and second orifices, respectively, first and second conduit connections, first and second fluid passages leading from said first and second conduit connections to said first and second apertures, respectively, a check valve interposed in said first passage and normally closed against fluid flow in said first passage from said first cylinder end, a movable plunger operatively aligned with said check valve and having an end adapted on subjection to fluid pressure to move said plunger for opening said check valve, a port branching from said second passage and leading to said plunger end; first valve means shiftable into first, second and third positions, with said valve means in said first position providing communication between a first fluid source of a given high-level pressure and said first conduit connection and simultaneously venting said second conduit connection, and in said second position providing communication between said first fluid source and said second conduit connection and simultaneously venting said first conduit connection; and a device for decreasing the pressure of operating fluid in said first cylinder end from said high-level pressure to a certain low-level pressure, including said first valve means, and further providing a vent, second valve means normally closed to intercept communication between said vent and first aperture, and having an end adapted on subjection to fluid pressure to open said second valve means for providing communication between said vent and first aperture, third, fourth and fifth passages, of which said fifth passage leads to said end of said second valve means, and said fourth passage leads to said first aperture, third valve means normally urged into a first position in which to provide communication between said third and fifth passages, and shiftable into a second position in which to provide communication between said third and fourth passages and vent said fifth passage, with said first valve means in said third position providing communication between a second fluid source of said certain low-level pressure and said third passage, intercepting communication between said first fluid source and said first conduit connection, and venting said second conduit connection, and control means operative in said third position of said first valve means to shift said third valve means into said second position on a pressure drop of fluid in said first aperture to a given minimum level below said low-level pressure, and retain it in said second position while said first valve means is in said third position.