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| Illustration 1 | g00487277 |
Hydraulic displacement control valve in a straight line operation (1) Feedback linkage (2) Oil from the charge pump (3) Servo cylinder (4) Pivot (5) Null adjustment (6) Barrel (7) Feedback spring (8) Signal passage (9) Spool (10) Signal passage (11) Orifices to case drain (EE) Charge oil (LL) Common sump | |
The hydraulic displacement control valve uses pilot oil from the steering control in order to determine the volume and the direction of oil flow from the steering pump. The pilot pressure shifts control spool (9). When control spool (9) shifts, pilot oil is directed to one end of the servo cylinder.
The angle of the swashplate is controlled by changing the pilot pressure at the servo cylinder. Pump output is controlled by the angle of the swashplate.
When no pilot pressure comes from the steering control, both ends of control spool (9) are open to the common sump through the steering control.
When there is no pilot pressure at either end of control spool (9), the centering springs hold the control spool in a NEUTRAL position. Charge pressure oil (2) is blocked from servo cylinder (3) by control spool (9). Both ends of servo cylinder (3) are open to the common sump across control spool (9) .
Right Turn in Forward or Left Turn in Reverse
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| Illustration 2 | g00487320 |
Hydraulic displacement control valve in a right turn in forward or in a left turn in reverse (1) Feedback linkage (2) Oil from the charge pump (3) Servo cylinder (4) Pivot (5) Null adjustment (6) Barrel (7) Feedback spring (8) Signal passage (9) Spool (10) Signal passage (11) Orifices to case drain (DD) Pilot oil (EE) Charge oil (JJ) Reduced charge oil (LL) Common sump | |
Feedback linkage (1) connects the steering pump's swashplate to control spool (9). When the steering pump's swashplate moves, feedback linkage (1) follows the movement. Feedback linkage (1) moves barrel (6) in the opposite direction of control spool (9) .
The movement of barrel (6) allows feedback spring (7) to center control spool (9). This stops the oil flow to servo cylinder (3) .
If the pilot pressure in signal passage (8) is not balanced against the force of the centering spring at the right end of control spool (9), the pilot pressure in signal passage (8) shifts control spool (9) again.
The shifting of control spool (9) allows metered pilot pressure to servo cylinder (3). This upstrokes the steering pump. Feedback linkage (1) forces control spool (9) to shift back and forth until the pressure and the spring forces are balanced.