Depth control apparatus

Claim 1

A hydraulic system comprising: (a) a main cylinder having first and second ends, a main piston, a floating piston, a first region defined by the space between said floating piston and said first end, a second region defined by the space between said floating piston and said main piston, a third region defined by the space between said main piston and said second end; said main piston including a stem extending outside said cylinder for transmission of fluid into and out of said second region; said first and second ends including first and second apertures respectively for transmission of fluid into and out of said first and third regions, respectively; passage means in said cylinder proximate said second end for permitting fluid communication between said second aperture and said second region when said main piston is substantially in abutment with said second end; (b) one way check valve means for preventing the flow of fluid into and out of said first aperture; (c) a slave cylinder having first and second ends, third and fourth apertures respectively in said ends, a second main piston, second passage means in said slave cylinder proximate said second end for permitting fluid to flow between said third and fourth apertures and around said second main piston; (d) first conduit means for connecting said second and third apertures; (e) control means for controlling the flow of fluid into and out of said first, second, third and fourth apertures, said control means having: (1) a first position thereof which disables said check valve means and permits the flow of fluid into said first aperture, out of said second aperture, into said third aperture and out of said fourth aperture, thereby causing said floating piston to move toward the second end, (2) a second position thereof which disables said check valve means and permits the flow of fluid into said fourth aperture, out of said third aperture, into said second aperture and out of said first aperture, thereby causing said floating piston to be moved toward said first end, (3) a third position thereof which allows the flow of fluid into said stem, out of said second aperture and into said third aperture, and out of said fourth aperture, thereby causing said main piston to move toward the second end, (4) a fourth position thereof which allows the flow of fluid into said fourth aperture, out of said third aperture to said second aperture, and out of said stem, thereby causing said main piston to move toward the first end.