SkyTrak 6036 Service Manual - Manual (Page 130)

Section 9. Hydraulic System
9-17 Model 6036 S/N 9B0499 and Before
9.1.6 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. 9.7.
2. When the steering wheel is turned, the se-
quence valve, Fig. 9.7, opens, permitting
supply pressure to be directed to the power
steering unit. If the supply pressure reaches
2475 ± 25 psi (170,5 ±1,7 bar), the steering
relief valve will be piloted open to allow
hydraulic oil to flow to the return filter and
reservoir.
3. The power steering unit consists of control
valve and metering sections, Fig. 9.7:
• 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 bidirectional gerotor
element. It meters (measures) the amount
of fluid sent to the steering cylinders.*
*Forklifts S/N 8F0235 and before may have a
counterbalance valve, Fig. 9.7.
4. The steering and emergency brake pump,
Fig. 9.7, provides limited backup hydraulic
supply pressure to the steering and brake
circuits in the event of engine stoppage or
tandem pump failure and during initial start-up
before the tandem pump is fully operational.
This pump is driven by an electric motor; it
also draws fluid through the suction strainer in
the reservoir.
The steering and emergency brake pump is
controlled by a oil pressure switch on the
engine which senses the engine oil pressure.
When the ignition switch is in RUN position
and the pressure switch is closed at oil
pressure below 4 psi (0,3 bar), the steering
and emergency brake pump is energized and
the pump will run. Output of the pump is 3
gpm at approximately 1500 psi (104 bar).
When the pressure rises above 4 psi (0,3 bar),
(engine running), the oil pressure switch
opens to stop the steering and emergency
brake pump.
No Steering Action
When no steering maneuver is being accom-
plished, the power steering control valve spool is
in the center or neutral position and fluid from the
tandem pump circulates through ports F to E, Fig.
9.7, of the control valve section directly back to the
reservoir. No fluid is directed to the steer select
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 B, Fig. 9.7, 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 C to D to port J in the
steer select valve.
3. Both steer select valve solenoids are de-
energized. Oil is channeled through ports J to I
of the steer select valve to the rod (retract)
end of the right front steering cylinder and
the base (extend) end of the left front steer-
ing cylinder.
4. Return hydraulic oil from the cylinders flows
through ports A to E of the power steering
control valve section to the return filter and
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 B, Fig. 9.7, 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 C to D to port J in the
steer select valve.