Upstroking (1) 14 1 2 4 6 15 LS pressure 12 13 X 21 22 10 L B 16 LS pressure oil System pressure oil Return oil L1 S 17 18 23 13 19 20 12 10 4 75796WE35 1 Drive shaft 2 Swash plate 4 Counter piston 6 Counter spring 10 Control piston 12 Pressure compensator spool 13 Flow compensator spool 14 Case drain 15 Passage 16 Passage 17 Spring 18 Spring 19 LS line from the metering pump 20 Cavity 21 Passage 22 Passage 23 Cavity Upstroking of the pump occurs as flow demand from loader and steering system. The increased flow demand causes a LS pressure in LS line (19). The LS pressure in LS line (19) combines with the force of spring (18) in cavity (20).
The force of spring (18) causes pump pressure to be higher than the LS pressure (19). If the combination of LS pressure and of spring force is greater than the pump discharge pressure, this difference pressure causes spool (13) to move right. As spool (13) moves right, the spool (13) blocks the flow of supply oil to control piston (10). Pump swash plate (2) is controlled by pressure and flow as much as hydraulic system requests. When the oil flow to control piston (10) is blocked, the pilot oil in passage (22) drains to passage (23). The oil then flows past pressure compensator spool (12) and through passage (16) into the housing and via the drain line (14) to tank.
Supply oil flows through passage (15) to counter piston (4). The oil acts against counter piston (4). The oil combines with the force of counter spring (6). This causes swash plate (2) to upstroke. This also causes the pump flow to increase. As flow requirements are satisfied, the pump output pressure increase. The pressure increases until the pressure in passage (15) moves flow compensator spool (13) up to be satisfied with system requirement for pressure and flow. В Pump discharge pressure = force of spring (18) + LS pressure (19) 6-14