TUBE AS 3598599 - Caterpillar

Illustration 3 g02836116
Metering Positions
(A) Spool position at high pump pressure. (B) Spool position at low pump pressure.
Slight side to side movement is called metering. Metering is done by equal forces on the spool (13).With spool (13) in position A, pump pressure is greater than the combined force of spring (18) and the signal oil pressure in cavity (20). This forces spool (13) to move right.When spool (13) moves right, pressure oil flows past the spool. The oil then flows through passage (23). The oil flows past cutoff spool (12) and into passage (22). Oil flows through passage (22) to control piston (10). This action causes the pump to destroke.The area of control piston (10) is larger than the area of bias piston (4). This difference causes the oil force acting against control piston (10) to overcome the combined spring (6) force and oil acting against bias piston (4). Control piston (10) 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 (20) and spring (18) causes spool (13) to move into B.When spool (13) moves left, the flow of pump output oil into passage (20) is blocked. Oil in passage (22) flows from control piston (10) past spool (12). The oil then returns to the case drain.Destroking
Illustration 4 g02765878
Pump and Compensator Operation
(1) Drive shaft
(2) Swashplate
(4) Piston
(6) Spring
(7) Pressure and flow compensator valve
(10) Control piston
(12) Pressure cutoff spool
(13) Margin pressure spool
(14) Case drain
(15) Passage
(16) Passage
(17) Spring
(18) Spring
(20) Cavity
(21) Passage
(22) Passage
(23) Cavity The decreased flow demand causes a signal pressure in cavity (20). The signal pressure in cavity (20) combines with the force of spring (18). This combination of signal pressure and of spring force is less than the pump pressure force in passage (15). This causes spool (13) to move to the right.The oil behind control piston (10) cannot flow through passage (16) to case drain (14). Pump oil now flows through passage (15). The oil then flows past spool (12), through passage (22), and then to control piston (10).The pump pressure behind control piston (10) is now greater than the combined force of bias piston (4) and of bias spring (6). The angle of swashplate (2) decreases. This action decreases the pump output and the system pressure.When the lower flow requirements are met, margin pressure spool (13) moves left to the metering position. Swashplate (2) maintains an angle that is sufficient to provide a pressure equal to the highest implement cylinder pressure. If the operator does not use the implements, then the pump will return to low-pressure standby.Low Pressure Standby
Illustration 5 g02765881
Pump and Compensator Operation
(1) Drive shaft
(2) Swashplate
(4) Piston
(6) Spring
(7) Pressure and flow compensator valve
(10) Control piston
(12) Pressure cutoff spool
(13) Margin pressure spool
(14) Case drain
(15) Passage
(16) Passage
(17) Spring
(18) Spring
(20) Cavity
(21) Passage
(22) Passage
(23) Cavity Low-pressure standby constitutes the following conditions: a running engine, inactive implements and level ground. There are no flow demands on the