Hunter Engineering Company

Joseph H Cox

Michael A Olsen

Paul W Roloff

Brian K Hierholzer

Richard A Killeen

An improved hydraulic circuit for a two-post lift having a master cylinder hydraulically connected to a slave cylinder. The master cylinder and slave cylinder are sized so fluid volume displaced at the rod end of the master cylinder is equal to the volume displaced at the piston side of the slave cylinder. The hydraulic circuit employs an automatic leveling valve assembly disposed to open when the lift reaches a fully lowered position to automatically equalize the displaced fluid volume of the master and slave cylinders so as to relevel the lift each time the lift is fully lowered. A sequence valve is positioned to pre-pressurize the slave cylinder before raising to compensate for any air in the circuit and fluid compressibility. A pilot operated check valve is designed to close and stop the descent of the lift in a level position if an obstruction is encountered under a side of the lift. Velocity sensor fuses connected to cylinder ports and actuated by a drop in pressure or rapid descent of the cylinders lock the cylinders in aligned positions in the event of a hydraulic leak.

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Chesterfield, MO, United States of America

Joseph H Cox