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| Illustration 1 | g01013339 |
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(1) Line to hoist control valve
(2) Line to diverter valve in hoist control valve (3) Pump drive (4) Single-section pump for the hoist and the rear brakes (5) Front pump section (6) Rear pump section (7) Lines from hydraulic tank | |
The oil that is used by the hoist system is supplied by two pumps. One pump is a two-section pump (5) and (6). This pump is located at the top rear of pump drive (3). The other pump is a single-section pump (4). The single-section pump is located at the bottom front of pump drive (3). All of the oil from the hoist pumps is combined through hoses and a check valve. The check valve maintains the two pumps as separate systems when the hoist lever is in the power down position. The check valve also helps to distribute the oil flow evenly. When the hoist is being raised, both pump sections are used. When the hoist is being powered down, only one pump section is used and the rest of the oil is used to cool the rear brakes. Whenever the hoist circuit is not being used, all of the oil from the two hoist pumps is used to cool the rear brakes. Refer to Specifications, "793B Off-Highway Truck Hydraulic System" for information on flow rates.
Oil from the hydraulic tank flows through line (7) to the inlet port of rear pump section (5). Pump section (5) pumps oil through line (1) to the hoist screen. The oil goes from the screen to a hoist relief valve. Two hoist relief valves are located on the hoist control valve. At the hoist relief valve, the oil is sent to one of two locations. When the dump body is being raised, the oil is sent to a junction block. At the junction block, this oil combines with the oil from the rear pump section (6). This combined flow of oil is supplied to the hoist cylinders. If this oil is not needed for the operation of the hoist, the oil is diverted to the oil coolers for the rear brakes.
Oil from the hydraulic tank flows through line (7) to the pump inlet port of front pump section (6). Pump section (6) then pumps oil through line (2) to the hoist screen. The oil goes from the screen to a hoist relief valve. Two hoist relief valves are located on the hoist control valve. At the hoist relief valve, the oil is sent to one of two locations. When the dump body is being raised, the oil is sent to a junction block. At the junction block, this oil combines with the oil from the front pump section (5). This combined flow of oil is supplied to the hoist cylinders. If this oil is not needed for the operation of the hoist, the oil is directed to the oil coolers for the rear brakes.
Single-section pump (4) receives oil from the hydraulic tank. The pump then sends this oil to the manifolds of the two-section pump. When the dump body is being raised, the oil from the single-section pump is combined equally with the oil from the two-section pump in order to provide additional oil flow for the hoist cylinders . When the dump body is not being raised, the single-section pump assists in cooling the oil for the rear brakes.