Gradall XL4000, Manual

Page: 55 / 327

XL 4100/5100 HYrDARAULIC SYSTEM OPERATIONS MANUAL Form No. 29703
Hoist Control Valve
The hoist valve consists of two port reliefs, a section compensator and compensator regulator.
See Figure 61
Fluid flows from the front port when the front end cap is pressurized. When the joystick is actuated, the pilot
signal shifts the valve spool and the compensator meters fluid to the spool. The spool then routes fluid to the
hoist cylinders. The valve load sense system controls compensator shift and signals the pump load sense system.
Hoist-down speed is controlled by valve spool notches. A craning hole in the spool brings the pump to the
proper pressure and supports the load in the boom circuit until pump output pressure is higher than circuit
pressure. If this circuit stalls while hoisting up, the regulator opens and allows the compensator to shift, cutting
off fluid to the hoist circuit until pressure drops below the regulator setting. Port relief on hoist-up (rear port)
protects against external loads. Port relief on hoist-down (front port) prevents excess down pressure and affects
stability. Hoist up speed is controlled by a stroke limiter on the front end cap.
Refer to “Appendix B” (XL 4100)
or “Appendix C” (XL 5100)
for correct hoist cycle time. Running faster than these specifications can cause
overheating of the hydraulic system. The maximum flow rates out of the “A” (front) and “B” (rear) ports are 15
and 41 GPM respectively.
FIGURE 61
HOIST VALVE SECTION
XV. Hoist Circuit
(continued)
Port Relief
“B” Port
Spool
“A” Port
Port Relief
Stroke
Limiter
Compensator
Spring
Section
Regulator
53