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| Illustration 1 | g06356625 |
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Main pump (1) Control spool (2) Solenoid (3) Outlet port (4) Main pump (5) Suction port | |
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| Illustration 2 | g06362359 |
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Main pump cutaway (6) Shaft (7) Housing (8) Piston shoe (9) Piston (10) Barrel (11) Valve plate (12) Slipper plate (13) Swashplate | |
No-Load Operation
The main pump (4) is a piston pump. Barrel (10) is incorporated in housing (7) of the main pump. Pistons (9) are contained in barrel (10). Each piston (9) forces the oil delivery from the pump through pump outlet port (3).
Shaft (6) of the main pump is directly coupled with the engine flywheel. Shaft (6) is also splined with barrel (10). The head of each piston (9) pivots on piston shoe (8). Piston shoes (8) are secured to slipper plate (12) by the retainer.
When shaft (6) is driven by the engine flywheel, barrel (10) turns on valve plate (11). This action allows pistons (9) to rotate on slipper plate (12). Slipper plate (12) is held to swashplate (13).
Oil from the hydraulic tank goes into the main pump through inlet port (5). The oil goes through the inlet passage of valve plate (11). The oil then enters the bores of barrel (10). As barrel (10) rotates, pistons (9) move in or out of the bores of barrel (10). Oil is drawn behind piston (9) into the bore of barrel (10) as piston (9) moves out of the bore. Oil is pushed ahead of piston (9) as the piston moves into the bore of barrel (10). The oil that is pushed ahead of each piston alternately goes through passages of valve plate (11). Piston (9) forces oil flow through outlet port (3) as main pump oil flow. The oil flow through port (3) goes to the main control valve.
The length of stroke for each piston (9) changes depending on the angle of swashplate (13). This change of displacement regulates the output flow of the pump.