PIPE AS 4484567 - Caterpillar

Illustration 3 g02817676
Metering Positions
(A) Spool position at high pump pressure. (B) Spool position at low pump pressure.
Slight right movement and slight left movement is called metering. Metering is done by equal forces on the spool (7).With spool (7) in position A, pump pressure is greater than the combined force of spring (13) and the signal oil pressure in cavity (15). This forces spool (7) to move right.When spool (7) moves right, pressure oil flows past the spool. The oil then flows through passage (18). The oil flows past cutoff spool (9) and into passage (17). Oil flows through passage (17) to control piston (6). This action causes the pump to destroke.The area of control piston (6) is larger than the area of bias piston (3). This difference causes the oil force acting against control piston (6) to overcome the combined spring (5) force and oil acting against bias piston (3). Control piston (6) moves to the left. This causes swashplate (2) to move toward the minimum angle.As the angle of swashplate (2) decreases, pump output also decreases. When pump pressure decreases enough, the combined force of signal pressure in cavity (15) and spring (13) causes spool (7) to move into position B.When spool (7) moves left, the flow of pump output oil into passage (18) is blocked. Oil in passage (17) flows from control piston (6) past spool (9). The oil then returns to the case drain.Destroking
Illustration 4 g03804316
(1) Drive shaft
(2) Swashplate
(3) Bias Piston
(4) Control Piston
(5) Spring
(6) Control piston
(7) Margin pressure spool
(8) Pressure and flow compensator valve
(9) Pressure cutoff spool
(10) Case drain
(11) Passage
(12) Spring
(13) Spring
(14) Signal line from the metering