Section 6
Hydraulic System
20425603
5-2005/Rev 0
6-3
The main system relief valve provides system protection by monitoring the oil pressure entering
the manifold. If the hydraulic pressure exceeds 3,400 psi (234 bar), the valve opens to limit the
pressure. The valve is factory calibrated and is not serviceable. A drain line from the valve
prevents oil from collecting behind the relief valve to ensure a constant pressure under all
operating conditions.
The hydraulic system operates at high or low pressure settings up to the maximum flow capacity
of the hydraulic pump. The high and low limit compensators mounted on the pump regulate the
flow of hydraulic fluid to maintain constant operating pressures. Operating pressures are set and
adjusted at the high and low pressure control valves on the manifold.
If the machine is equipped with proportional pressure control, low pressure is adjusted at the
manifold, and the high pressure setting is made from the controller.
The high and low limit compensators regulate the flow of hydraulic fluid to the
system by controlling the angle of the swashplate. If the oil is not properly
maintained, the compensators can become blocked with debris. As a result, pump
control will be lost and you will not be able to create hydraulic oil pressure.
The normally closed, two position solenoid valve is controlled by the operator’s selection of high
or low pressure. The valve is closed while operating in high pressure and is open during low
pressure operation. A light on the solenoid connector indicates low pressure operation.
A reference gauge on the top of the manifold displays hydraulic pressure to the intensifier. When
the intensifier shifts, it is normal for the pressure to quickly fall and then rise again.
The directional valve consists of a spool with internal passages that direct hydraulic flow to one
end while returning fluid to the reservoir through the opposite end. Spool position is controlled
by a pair of solenoids, one at each end of the spool. The solenoids are alternately energized in
response to the position of the hydraulic piston as the proximity switch detects the end of the
stroke.
On redundant models, the 4-way directional control valve directs pressurized oil to one end of the
hydraulic cylinder and returns fluid to the reservoir from the opposite end, causing the intensifier
to stroke. The movement is controlled hydraulically by a pilot valve, electrically operated by two
solenoids. Indicators light up as each solenoid is energized. The directional control valve sends
flow to the hydraulic cylinder in one direction until the hydraulic piston activates the proximity
switch at the end of the stroke. The activated switch sends a signal to the controller to reverse the
direction of flow. The piston then moves in the opposite direction until it activates the proximity
switch at the opposite end of the stroke.
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