Apparatus for disabling an obstructed lift mechanism

• US 4,638,886 A
• Filed: 10/21/1985
• Issued: 01/27/1987
• Est. Priority Date: 10/21/1985
• Status: Expired due to Term

• Current Assignee: Danfoss Fluid Power A/S
• Original Assignee: Sta-Rite Industries LLC (Pentair Plc (Ireland))
• Inventors: Marietta, Walter E.
• Primary Examiner(s): Rolla, Joseph J.
• Assistant Examiner(s): Pedersen, Nils E.
• Application Number:
  US06/789,516
• Time in Patent Office: 463 Days
• Field of Search: 187/8.41, 187/8.47, 187/8.49, 187/8.5, 187/9 R, 187/9 E, 187/17, 254/89 H, 91/517, 91/520, 91/445
• US Class Current: 187/215
• CPC Class Codes: B66F 7/04 hydraulically or pneumatically operated

Abstract

An apparatus for disabling an obstructed lift mechanism having at least two hydraulic cylinders for controllably lifting and lowering a load includes a pair of valves, each arranged for sensing the differential pressure between a first sensing line and a second sensing line. The first valve is movable to a position for preventing the flow of hydraulic fluid from a first cylinder when the pressure in the second sensing line exceeds that in the first sensing line by a first predetermined value. The second value is movable to a position for preventing the flow of hydraulic fluid from the first cylinder when the pressure in the first sensing line exceeds that in the second sensing line by a second predetermined value. If the flow of hydraulic fluid from the first cylinder is prevented by the movement of either the first valve or the second valve, the operator is required to lift the load slightly to remove the obstruction.

Claims

1. An apparatus for disabling an obstructed lift mechanism having at least two hydraulic cylinders employed for controllably lifting and lowering a load, said apparatus including:

a first valve for sensing the differential pressure between a first sensing line and a second sensing line;

a second valve for sensing said differential pressure between said first sensing line and said second sensing line;

said first valve being movable to a position for preventing the flow of hydraulic fluid from a first cylinder when the pressure in said second sensing line exceeds the pressure in said first sensing line by a first predetermined value;

said second valve being movable to a position for preventing the flow of hydraulic fluid from said first cylinder when the pressure in said first sensing line exceeds the pressure in said second sensing line by a second predetermined value.

2. The invention set forth in claim 1 wherein said first sensing line is connected in a pressure-sensing relationship to said first cylinder and said second sensing line is connected in a pressure-sensing relationship to said second cylinder.

3. The invention set forth in claim 2 wherein said first cylinder and said second cylinder are connected in series.

4. The invention set forth in claim 3 wherein said first predetermined value and said second predetermined value are substantially equal one to the other.

5. A hydraulic system for preventing the lowering of a mechanically obstructed lift mechanism and including:

a first cylinder having its head end connected by a first conductor to a source of pressurized fluid;

a second cylinder having its head end connected by a second conductor to the rod end of said first cylinder for permitting fluid flow therebetween;

a first valve movable between a first position for permitting fluid to flow from said first cylinder and a second position for preventing fluid from flowing from said first cylinder, said first valve including a first pilot port for sensing the hydraulic pressure in said first conductor and a second pilot port for sensing the hydraulic pressure in said second conductor;

a second valve movable between a first position for permitting fluid to flow from said first cylinder and a second position for preventing fluid from flowing from said first cylinder, said second valve including a first pilot port for sensing the hydraulic pressure in said first conductor and a second pilot port for sensing the hydraulic pressure in said second conductor;

said first valve being normally biased to said first position and piloted to said second position when said hydraulic pressure in said second conductor exceeds the pressure in said first conductor by a first predetermined value;

said second valve being normally biased to said first position and piloted to said second position when said hydraulic pressure in said first conductor exceeds the pressure in said second conductor by a second predetermined value.

6. The invention set forth in claim 5 wherein said first valve and said second valve each include a passage for permitting fluid to flow from said first cylinder and said passages are connected in a series flow relationship one with the other.

7. The invention set forth in claim 6 wherein said first predetermined value and said second predetermined value are substantially equal one to the other.

8. A hydraulic system for preventing the lowering of a mechanically obstructed lift mechanism and including:

a first cylinder having its head end connected by a first conductor to a source of pressurized fluid;

a second cylinder having its head end connected by a second conductor to the rod end of said first cylinder for permitting fluid flow therebetween;

a valve movable between a first position for permitting fluid to flow from said first cylinder and a second position for preventing fluid from flowing from said first cylinder, said valve including a first pilot port for sensing the hydraulic pressure in said first conductor and a second pilot port for sensing the hydraulic pressure in said second conductor;

said valve being further movable between said first position for permitting fluid to flow from said first cylinder and a third position for preventing fluid from flowing from said first cylinder, said valve being normally maintained at said first position and piloted to said second position or to said third position when said hydraulic pressure in one of said conductors exceeds the pressure in the other of said conductors by a predetermined value.

9. The invention set forth in claim 8 wherein said valve is of the three position, spring centered, two way type.