BRACKET-YM 4181939 - Caterpillar

Illustration 3 g00488089
(1) Flow Compensator Spring (2) Pressure Compensator Spring (3) Line to Control Valve (4) Actuator Piston (5) Swashplate (6) Signal Line from Control Valve (7) Cavity (8) Flow Compensator Spool (9) Pressure Compensator Spool (10) Passage (11) Passage (12) Passage (13) Passage (14) Case Drain (15) Bias Spring (16) Bias Piston (BB) High Pressure Oil (DD) Low Pressure Oil (LL) Return OilDestrokingDestroking occurs when the signal pressure decreases due to a low load at high pump output. The lowest signal pressure goes through line (6) and the oil fills cavity (7). The signal pressure plus the force of spring (1) move spool (8) upward. Oil behind actuator piston (4) cannot go to case drain (14). Pump oil now flows through passage (11), past spool (8), through passage (10) and into actuator piston (4). Pump pressure behind actuator piston (4) is now greater than the combined force of bias spring (15) and bias piston (16). The angle of swashplate (5) decreases. This decreases pump output. When pump pressure is reduced to a certain point, the combined signal and spring force in cavity (7) moves spool (8) downward. The oil pressure behind actuator piston (4) goes back to the case drain. Bias piston (16) and spring (15) force the angle of swashplate (5) to increase. This slight up and down spool movement is called metering. Metering keeps the pressure on both ends of spool (8) equal. The force of spring (1) is equal to 1720 kPa (249.5 psi). Therefore, pump pressure is 1720 kPa (249.5 psi) greater than signal pressure. This difference is called margin pressure.As system pressure approaches the 1720 kPa (249.5 psi) margin pressure or 3200 kPa (464.1 psi) low pressure standby, flow compensator spool (8) moves downward to the metering position. The angle of swashplate (5) increases slightly in order to maintain the lower required pressure.
Illustration 4 g00488123
(1) Flow Compensator Spring (2) Pressure Compensator Spring (3) Line to Control Valve (4) Actuator Piston (5) Swashplate (6) Signal Line from Control Valve (7) Cavity (8) Flow Compensator Spool (9) Pressure Compensator Spool (10) Passage (11) Passage (12) Passage (13) Passage (14) Case Drain (15) Bias Spring (16) Bias Piston (BB) High Pressure Oil (DD) Low Pressure Oil (LL) Return OilHigh Pressure StallHigh pressure stall occurs when pump output reaches 24800 kPa (3597.0 psi). Signal pressure in line (6) and cavity (7) now equals pump output pressure. The force of spring (1) moves spool (8) downward. When system pressure reaches 24800 kPa (3597.0 psi) in passage (11), the force on pressure compensator spool (9) compresses spring (2). Pressure compensator spool (9) moves upward. Supply oil flows through passage (10) to actuator piston (4). This decreases pump output. System pressure remains constant at 24800 kPa (3597.0 psi). If the control lever is moved to the HOLD position, the signal pressure in cavity (7) flows through signal line (6). The oil flows through the control valve. The oil then goes back to the tank. System pressure begins to decrease. At approximately