Description and Operation
2000 SRM 1233
Description and Operation
HYDRAULIC OIL SUPPLY
Two gear pumps supply the flow of oil for the com-
ponents of the hydraulic system. These pumps are
driven by a gear arrangement in the torque converter
housing. The inlet hose for each gear pump is con-
nected to the hydraulic tank with a manual shutoff
valve.
The cover end section of the right-hand tandem pump
supplies oil to the accumulator charge valve for the
brake pilot system, auxiliary section, and lift section.
The shaft end section of this tandem pump supplies
oil for the single spool main control valve (lift sec-
tion).
The cover end section of the left-hand tri-section
pump circulates oil in tank through heat exchanger
circuit and oil-cooled brakes. The shaft end section of
this pump supplies oil to flow amplifier for steering
system. Oil that is not needed for steering flows from
flow amplifier to the two spool main control valve
(tilt/lift section). When the operator is not steering,
all of oil from pump flows to main control valve.
NOTE:
Oil that is returned to the hydraulic tank is
filtered.
MANIFOLD, SECTION 1 OF HYDRAULIC
PLATE
The relief valve limits input oil pressure supplied
to accumulator charge valve to 28 MPa (4061 psi),
and forces oil to flow through a high pressure oil
filter (20 micron), if oil is needed to charge the ac-
cumulator. See Figure 2. The accumulator charge
valve controls charging rate and pressure of oil in
the accumulator for brake/pilot system. The accu-
mulator charge valve stops charging when accumu-
lator pressure reaches upper limit. See Measure-
ments and Adjustments. When accumulator pres-
sure reaches lower limit, see Measurements and Ad-
justments, the accumulator charge valve allows oil
from pump to charge accumulator. Adjustment at
the spring of check valve in accumulator charge valve
sets high and low limit pressure at accumulator. This
pressure can be measured at check port MACC.
Oil pressure from accumulator is supplied to brake
treadle.
The right-hand pedal only activates the
service brakes. The left-hand pedal first disengages
the transmission, then the service brakes will be
activated. Both pedals will engage the brake pres-
sure switch to operate the stop lights. For brake
treadle pressures, see Measurements and Adjust-
ments. Brake pressure can be measured at check
port MSB4.
Oil pressure from accumulator is also supplied to the
pressure switch that operates the warning light in
event of low brake pressure and to the solenoid valve
for the parking brake. Both are integrated in the cab
manifold. See Figure 2. The solenoid valve can be op-
erated by a switch located on the instrument panel.
The solenoid valve is normally energized during op-
eration for oil pressure to compress the spring to re-
lease parking brake. For further information on the
brake circuit, see the section Service Brake 1800
SRM 1038.
The reducer valve for the pilot is set at 5 MPa
(725 psi) and controls the pressure and supply of hy-
draulic oil to pilot circuits for remote control valves
for lift, tilt, and auxiliary. See Figure 2. The setting
can be checked at check port MPLT.
MAIN CONTROL VALVE, SECTION 2 OF
HYDRAULIC PLATE
Description
The main control valve controls the operation of the
lift (2 sections), tilt and auxiliary cylinders. See Fig-
ure 3. The main control valve is fastened to a plate
in the frame. The valve is also divided into a lift/tilt
section, lift section and auxiliary section. Every sec-
tion has it’s own primary relief valve, set on 23.5 MPa
(3410 psi). The tilt section has an impact relief valve,
set on 25 MPa (3625 psi), which is activated during
contact and opens a tank line to allow the mast to tilt
backward.
Each section of the valve has a spool and valve body.
On the fork lift truck, the control spools for the tilt
and auxiliary are the same, however a different type
of spool is used in the lift section of the valve. All
spools have metering notches to improve the control
of oil flow. When a lever is operated, a pilot pres-
sure is generated and activates the end of a spool.
Each spool has springs that return the spool to the
NEUTRAL position as soon as the control lever is
released. The spring package is different in every
section.
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