770G and 772G Off-Highway Truck (OEM) Hydraulic and Braking System: Hoist Cylinder

Typical hoist cylinders (1) Rod assembly (2) Cylinder (second stage)(3) Cylinder (first stage)

Cross section of hoist cylinder (1) Rod assembly (2) Cylinder (second stage) (3) Cylinder (first stage) (4) Grooves in the end of the cylinder (second stage) (5) Chamber in the head end of the hoist cylinder (6) Opening to the head end of the hoist cylinder (7) Opening to the rod end of the hoist cylinder (8) Chamber between cylinders (first stage and second stage) (9) Chamber between the rod assembly and cylinder (second stage) (10) Orifices in the rod assembly (11) Head (12) Internal head(13) Piston

Raising the Truck Body

Hoist cylinder (first stage) to extended length (1) Rod assembly (2) Cylinder (second stage) (3) Cylinder (first stage) (4) Grooves in the end of the cylinder (second stage) (5) Chamber in the head end of the hoist cylinder (6) Opening to the head end of the hoist cylinder (7) Opening to the rod end of the hoist cylinder (8) Chamber between cylinders (first stage and second stage) (9) Chamber between the rod assembly and cylinder (second stage) (10) Orifices in the rod assembly (11) Head (12) Internal head (13) Piston (AA) Pump oil(LL) Return oil

Extended hoist cylinder (1) Rod assembly (2) Cylinder (second stage) (3) Cylinder (first stage) (4) Grooves in the end of the cylinder (second stage) (5) Chamber in the head end of the hoist cylinder (6) Opening to the head end of the hoist cylinder (7) Opening to the rod end of the hoist cylinder (8) Chamber between cylinders (first stage and second stage) (9) Chamber between the rod assembly and cylinder (second stage) (10) Orifices in the rod assembly (11) Head (12) Internal head (13) Piston (AA) Pump oil(LL) Return oil

Two hydraulic cylinders are used to move the truck body away from the truck. When the hoist control is held in the RAISE position, the pump oil extends the two-stage cylinders and the truck body is raised to the dump position.

The hoist cylinders raise the truck body in two stages. The pump oil flows into opening (6) to the head ends of the hoist cylinders. The oil flows through a tube in rod assembly (1) and into chamber (5) in the head end of cylinder (3). The pressure of the pump oil in chamber (5) moves cylinder (3) .

The oil in chamber (8) must now flow through grooves (4) in the end of cylinder (2) and into chamber (5) .

When head (11) on the end of cylinder (3) reaches a lip on the end of cylinder (2), the cylinder is also pushed up by the oil in chamber (5). The oil in chamber (9) now flows through orifices (10), through the tube in rod assembly (1), and through opening (7) to the hoist control valve.

Cylinder (2) is pushed until internal head (12) on the end of cylinder (2) contacts piston (13), which is bolted to the top of rod assembly (1). When cylinder (3) is against the end of cylinder (2) and cylinder (2) is against the end of rod assembly (1), the hoist cylinder is fully extended.

Lowering the Truck Body

Retracted hoist cylinder (second stage) (1) Rod assembly (2) Cylinder (second stage) (3) Cylinder (first stage) (4) Grooves in the end of the cylinder (second stage) (5) Chamber in the head end of the hoist cylinder (6) Opening to the head end of the hoist cylinder (7) Opening to the rod end of the hoist cylinder (8) Chamber between cylinders (first stage and second stage) (9) Chamber between the rod assembly and cylinder (second stage) (10) Orifices in the rod assembly (11) Head (12) Internal head (13) Piston (AA) Pump oil(LL) Return oil

Move the hoist control to the LOWER position or to the FLOAT position in order to lower the truck body to the truck frame.

When the hoist cylinders are fully extended and the hoist control is moved to the LOWER position, pump oil retracts only cylinder (2). When cylinder (2) is fully retracted, gravity moves cylinder (3) and the truck body lowers onto the truck frame.

The truck body is lowered when the pump oil flows through opening (7), into rod assembly (1), through orifices (10), and into chamber (9) between the rod assembly and cylinder (2). The oil pushes cylinder (2) and cylinder (3) downward as chamber (9) is filled with pump oil. When the truck body gets to a specified position, flow that is leaving opening (6) will be restricted. This traps oil in chamber (5). The weight of the truck body continues to move cylinder (3) slowly. The weight of the truck body moves cylinder (3) downward until the cylinder is fully retracted. The oil in chamber (5) is pushed through the tube in rod assembly (1) and through opening (6) to the hoist control valve. The hoist control valve routes the oil to the hydraulic tank.

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770G and 772G Off-Highway Truck (OEM) Hydraulic and Braking System: Hoist Cylinder 2013-01-04T14:34:00-08:00 Rating: 4.5 Diposkan Oleh: Unknown