Automatic hydraulic lift circuit

In a two-post hydraulic lift having a master cylinder hydraulically connected to a slave cylinder, at least one load bearing member connected to the cylinders and a conventional hydraulic circuit to actuate the cylinders, the improvement in the hydraulic circuit comprising:

• an automatic leveling means for releveling the load bearing member each time the load bearing member is in a fully lowered position;
• an automatic equalization valve disposed to allow fluid to flow from said slave cylinder through said hydraulic circuit to a reservoir thereby equalizing the hydraulic fluid displaced within each said cylinder;
• an actuator mounted on a low surface of said load bearing member disposed to open said automatic equalization valve when said load bearing member is in a fully lowered position;
• and
• a check valve disposed to stop fluid flow from flowing backward through said automatic equalization valve when the lift is actuated.

In a two-post hydraulic lift having a master cylinder hydraulically connected to a slave cylinder, a load bearing member connected to each said cylinder, and a hydraulic circuit to actuate the cylinders, an improvement in the hydraulic circuit comprising:

• a hydraulic displacement ratio between said master cylinder and said slave cylinder such that fluid displaced at a rod end of said master cylinder is equal to fluid displaced at a piston end of said slave cylinder providing synchronization between said cylinders;
• an automatic leveling means for releveling the load bearing member each time the load bearing member is in a fully lowered position, said automatic leveling means having an automatic equalization valve disposed to open to allow fluid to flow from said slave cylinder through said hydraulic circuit to a reservoir thereby equalizing fluid displacement within said cylinders when said automatic equalization valve is actuated and a check valve to stop said fluid from flowing backward through said automatic equalization valve when said lift is raised;
• an actuator mounted on a lower surface of said load bearing member disposed to open said automatic equalization valve when said load bearing member is in a fully lowered position;
• and
• a sequence valve means for pre-pressurizing said slave cylinder prior to raising thereby compensating for air and fluid compressibility in said circuit.

A fluid driven two-post lift assembly comprising:

• a master cylinder having a rod end and a piston end;
• a slave cylinder having a rod end and a piston end hydraulically connected to said master cylinder, each said cylinder sized so fluid displaced at said rod end of said master cylinder is equal to the fluid displaced at said piston end of said slave cylinder, thereby synchronizing movement of said cylinders;
• at least one load bearing member operatively connected to said cylinders;
• a hydraulic circuit to actuate said cylinders;
• a pilot operated check valve means disposed within said circuit to close and stop said cylinders in an aligned position when an obstruction is encountered under a side of said load bearing member when said load bearing member is being lowered;
• a plurality of velocity sensor fuse means within said circuit disposed to close and lock said cylinders in place when said velocity sensor means detects an excessive flow rate or velocity of cylinder movement;
• and
• an automatic hydraulic leveling means for leveling said load bearing member each time said load bearing member is in a fully lowered position.