IMPLEMENT HYDRAULIC SYSTEM CONTINUED
2. Low Pressure Standby Continued
When an implement hydraulic circuit requires flow, the pressure from the pump outlet (Figure 4, Item 4) is reduced.
The combined force of the margin spring (Figure 4, Item 5), the boost pressure (Figure 4, Item 6), and the load
sensing oil pressure is greater than the supply pressure from the pump outlet. The overall force is on the top end of
the flow compensator (margin) spool (Figure 4, Item 7). In turn, the flow compensator (margin) spool moves
downward and blocks the flow of oil to the actuator piston (Figure 4, Item 3). Oil in the chamber of the actuator
piston vents to the case drain across the flow compensator (margin) spool. This allows the bias spring (Figure 4,
Item 2) to move the swashplate (Figure 4, Item 8) to a greater angle, and the implement pump (Figure 4, Item 1)
produces more flow. This condition is known as upstroking.
The following conditions can result in upstroking the implement pump (Figure 4, Item 1):
If an implement hydraulic circuit is initially activatedfrom low-pressure standby, the load sensing (signal) oil
increases pump output flow. The increased flow routes to the position of a main control spool of a hydraulic
control valve that demands the oil.
When theflow demand increases from changing the position of the main control spool in a hydraulic control
If another implement hydraulic circuit is engaged.
If theflow demand on the implement hydraulic system remains constant or increases and engine speed
Figure 4. Low Pressure Standby.