Hydraulic circuit with selectively actuatable float control

Claim 1

In a hydraulic system for selectively positioning a work member in selected fixed positions the combination comprising: a linear double-acting hydraulic motor connected to a work member, a source of fluid pressure including a sump and a pump for supplying fluid for operating said motor, a three position directional control valve in a valve housing and having a neutral position, and raise and lower positions for selectively directing fluid from said source to either end of said motor for operation of said motor for positioning said work member, a single control lever for operating said control valve, lock valve means including first and second passage means communicating said fluid respectively with alternate ends of said motor, check valve means disposed in each said passage means to normally block flow of said fluid from said motor and including pressure-responsive piston and plunger means in each said passage means for unseating said check valve means to provide communication between both ends of said motor and sump by way of said directional control valve, said check valve means disposed between said control valve means and said hydraulic motor for normally locking said motor in a selected position; solenoid operated auxiliary valve means separate spaced from and independent of said directional control valve and valve housing disposed between said source of fluid pressure and said lock valve means for bypassing said directional control valve for directing fluid solely to each said piston and plunger means solely for unseating each said check valve means for communicating both ends of said motor with said sump by way of said directional control valve for enabling free floating movement of said hydraulic motor when said main control valve is in a neutral position between said raise and said lower positions.