JLG 1850SJ Service Manual - Manual (Page 258)

SECTION 5 - BASIC HYDRAULIC INFORMATION & HYDRAULIC SCHEMATICS
5-88 – JLG Lift – 3121619
5.7 FUNCTION PUMP
Pump Operation
The variable pump converts input torque to hydraulic power.
Rotational force is transmitted through the input shaft to the
cylinder block. The input shaft is supported by tapered roller
bearings at the front and rear of the pump and is splined into
the cylinder block.
The cylinder block contains nine pistons. Each piston has a
brass slipper connected at one end by a ball joint. Slippers are
held to the swashplate by the spring retainer and block spring.
The block spring holds the cylinder block to the valve plate.
Reciprocating movement of pistons occurs as slippers slide
against the inclined swashplate during rotation.
The bias spring pushes against the servo piston which pulls
the swashplate causing the pump to stroke. Internal pressure
on the servo piston acts against the bias spring to reduce
swashplate angle causing the pump to de-stroke. Swashplate
angle determines pump outlet flow. The pump control sets
swashplate angle by metering system pressure to the servo
piston.
Load Sensing (LS) control with Pressure
Compensator (PC)
The LS control consists of two spool valves that connect the
servo piston either to pump case or system pressure.
The PC spool controls the pressure-compensating function of
the control. The LS spool controls the load-sensing function.
The PC spool has priority over the LS spool.
Figure 5-115. Function Pump Components
Figure 5-116. Control Assembly Components