Fluid operated circuit for controlling a dual post hydraulic lift

Abstract

A fluid operated circuit for controlling the movement of pistons contained in the drive and idler cylinders of a conventional dual post vehicle lift assembly of the type wherein the cylinders are hydraulically connected in tandem so that movement of the idler cylinder piston is dependent upon movement of the drive cylinder piston and wherein the pistons, while operative to lift and lower movable article supporting structures, are not fixedly connected thereto. The circuit employs a pilot operated check valve responsively connected to the lower ends of the two cylinders for preventing the drive cylinder piston from descending when the article supporting structure associated with the idler cylinder is locked or jammed in an elevated postion, a first tow-position control valve for perventing the drive cylinder piston from descending when the article supporting structure associated with the drive cylinder is locked or jammed, a simple check valve connected in shunting relation across the first control valve for restoring the latter to an open state after it has closed, and a second two-position control valve which is manually operated as desired to drain hydraulic fluid from the drive cylinder to permit lowering of the pistons and their associated article supporting structures so long as both of the latter are free of restraint.