SkyTrak 6036 Service Manual - Manual (Page 179)

Section 9 Hydraulic System
Model 6036/6036T S/N 9B0500 thru 14833 9-29
9.4.6 Power Steering Circuit
a. Description
1. Hydraulic pressure is applied in the power
steering circuit by the 15 gpm section (front
half) of the tandem pump, which draws its
fluid through a suction strainer in the reser-
voir, Fig. 9.16.
2. When the steering wheel is turned, the se-
quence valve, Fig. 9.16, opens, permitting
supply pressure to be directed to the load
sensing steering priority valve. The load
sensing steering priority valve spool will be
positioned so supply pressure is applied
through ports D to B, Fig. 9.16, to the intake
side of the power steering metering section.
If the supply pressure reaches 2850 ± 150 psi
(196,4 ± 10,3 bar), the steering relief valve
will be piloted open to allow hydraulic oil to
flow to the return filter in reservoir. When
the steering wheel is not turned the load
sensing steering priority valve spool will be
spring positioned so supply pressure is
applied through ports C to A, Fig. 9.16, to the
secondary control valve.
3. The load sensing steering priority valve
provides:
• Smooth pressure compensated steering
because pressure variations in the steer-
ing circuit do not affect steering response
or maximum steering rate.
• True power beyond system capability by
splitting the system into two independent
circuits. Pressure transients are isolated
in each circuit. Only the flow required by
the steering maneuver goes to the steer-
ing circuit. Flow not required for steering
is available for use in the secondary
control valve sections using the 15 gpm
section of the tandem pump.
• Provides reliable operation because the
steering circuit always has flow priority.
4. The power steering unit consists of control
valve and metering sections, Fig. 9.16.
• The control valve section contains a
mechanically actuated linear spool which
is torsion bar centered and is of the open
center type. It directs fluid to and from the
metering section and steering cylinders
and regulates the pressure supplied to the
steering cylinders.
• The metering section consists of a
commutator and a bi-directional gerotor
element. It meters (measures) the amount
of fluid sent to the steering cylinders.
No Steering Action
When no steering maneuver is being accom-
plished, the load sensing steering priority valve
spool is positioned so the fluid from the tandem
pump is channeled through ports C to A, Fig. 9.16,
of the load sensing steering priority valve to the
secondary control valve. No fluid is directed to the
power steering control valve or the steering
cylinders.
Left Turn - 2 Wheel Steer
When a left turn is being made with the steering
select switch in 2 wheel steer (center position):
1. The power steering control valve spool is
shifted so that supply pressure is applied
through ports F to C, Fig. 9.16, to the intake
side of the power steering unit metering
section.
2. A measured amount of hydraulic oil is ex-
hausted from the metering section and routed
back to the control valve section where it is
channeled through ports B to A to the base
end of the right front steering cylinder and the
rod end of the left front steering cylinder.
3. Return hydraulic oil from each of the front
steering cylinders flows through ports J to K of
the steer select valve and through ports D to E
of the power steering control valve to the
return filter in the reservoir.
Left Turn - 4 Wheel Steer
When a left turn is being made with the steering
select switch in 4 wheel steer (up position):
1. The power steering control valve spool is
shifted so that supply pressure is applied
through ports F to C, Fig. 9.16, to the intake
side of the power steering unit metering
section.
2. A measured amount of hydraulic oil is ex-
hausted from the metering section and routed
back to the control valve section where it is
channeled through ports B to A to the base
end of the right front steering cylinder and the
rod end of the left front steering cylinder.