Lull 6K Service Manual - Manual (Page 214)

Supply, Pressure, and Return Hydraulics
5-70 Service Manual — Models 644B, 6K, 844C, 8K, 1044C, 10K
Hydraulic Manifold Assembly Functions
Accumulator Charging
Hydraulic fluid is taken from hydraulic reservoir and flows through the
hydraulic pump, through the control valve, through the pump unloader, and
on to the hydraulic control manifold. Flow comes in P2 port and goes
through the Priority Flow (PF) valve. Three gpm of flow is split off and flows
through the Logic (LC) element and back to the PF valve. The circuit is
then combined with input flow (P2). When accumulator pressure is below
1200 psi, the Pilot Unloading (PU) valve shifts – pressurizing backside of
LC spool, allowing the 3 gpm to charge the accumulator through the Check
Valve (CV). When pressure reaches 1600 psi, the PU valve shifts,
dumping pilot signal on LC valve, allowing the three gpm to flow out
Excess Flow (EF) port.
Steering
The steering circuit is designed to be a load-sense, on-demand circuit. No
flow goes through steering until steering wheel is turned. When the
steering wheel is turned, only the flow required for steering is taken off the
hydraulic pump through the P1 port. Steering flow is proportional to
steering rotation. The maximum pressure on Controlled Flow (CF) port is
2250 psi. The pressure can be checked at the steering diagnostic port
(see Fig. 5-58 on page 5-90).
Pressure Reducing
When engine is started, Pilot Directional (PD) valve shifts, allowing flow
through the Pressure Reducing (PR) valve (450 psi) to activate the
joysticks. When engine shuts down, PD valve shifts to deactivate the
joysticks.