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| Illustration 1 | g00649449 |
The counterbalance valve is located on the tailgate cylinder. | |
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| Illustration 2 | g00649450 |
Counterbalance valve (1) Fitting (2) Valve body (3) Check valve (4) Port to the rod end of the hoist cylinders (5) Plug (6) Hole for pilot oil (7) Pilot port (8) Piston (9) Spool (10) Relief valve cartridge (11) Spring (12) Holes (13) Holes | |
The counterbalance valve is attached directly to the tailgate cylinder. Fitting (1) holds valve body (2) in position at the head end of the tailgate cylinder. Fitting (1) also allows the oil to flow in both directions freely.
The rod end lines of the hoist cylinders are connected to the head end of the tailgate cylinder through the counterbalance valve. The head end lines of the hoist cylinders are connected directly to the rod end of the tailgate cylinder. A pilot line connects the head end lines to the counterbalance valve.
When the RAISE operation is selected, oil flows from the hoist control valve to the head ends of the hoist cylinders and oil flows to the rod end of the tailgate cylinder. The pressure that is developed in the hoist cylinders is transmitted through pilot port (7) and hole (6) to piston (8). When the pressure reaches a preset level, piston (8) moves against the force of spring (11). This causes spool (9) to move away from check valve (3) .
As the pressure in the rod end of the tailgate cylinder retracts the tailgate cylinder in order to open the tailgate, oil flows from the head end of the tailgate cylinder through fitting (1), holes (12, 13), and port (4). This oil returns to the hydraulic tank through the rod end lines of the hoist cylinders.
When the tailgate cylinder is fully retracted, the flow of pilot oil stops and spring (11) moves spool (9) and piston (8). When the end of spool (9) seats against check valve (3), the flow of return oil through port (4) is stopped.
When the LOWER operation is selected, oil flows from the hoist control valve to the rod ends of the hoist cylinders and oil flows through port (4) of the counterbalance valve. The oil passes through holes (12), check valve (3), and fitting (1) into the head end of the tailgate cylinder in order to close the tailgate. When the tailgate cylinder is fully extended, check valve (3) closes. This prevents a reverse flow of oil through the counterbalance valve in order to hold the tailgate closed.