Accumulators; Steering/Brake Pump - Komatsu 830E Shop Manual

ACCUMULATORS

The accumulators (6, Figure 4-1) are a bladder type.
The accumulators are charged to 1400 psi (9.7 MPa)
with pure dry nitrogen.
Oil entering the accumulator pushes the bladder
upward compressing the nitrogen. The nitrogen pres-
sure increases directly with steering circuit pressure.
When brake/steering circuit pressure reaches 3500
to 3550 psi (24.5 to 24.85 MPa), the unloader valve
will unload the pump output to approximately 400 psi
(2.8 MPa). The accumulators will contain a quantity
of oil under pressure available for steering the truck.
When system pressure drops to 3200 psi (22.4
MPa), the pump output will again increase to refill the
accumulators and increase steering system pres-
sure. The accumulators also provide oil, for a limited
amount of use, to be used in case of an emergency
situation should the pump become inoperative.
Low Precharge Warning Switch
Pressure switches located in the top of each accu-
mulator monitor nitrogen pressure and are used to
activate the accumulator precharge warning light if
the nitrogen pressure drops below 1100 psi (7.6
MPa).
The switches monitor nitrogen pressure when the
key switch is turned ON and before the engine is
started. If nitrogen pressure is too low, the warning
lamp turns ON - a latching circuit prevents the warn-
ing lamp from turning off when the engine is started
and steering system pressure compresses the nitro-
gen remaining in the accumulator.
Do not operate the truck with less than 1100 psi
(7 584 kPa) nitrogen precharge in the accumula-
tors because there may be inadequate oil supply
in some emergency conditions. If low nitrogen
precharge pressure is determined, recharge the
accumulators to 1400 psi (9 653 kPa).
L04037
HIGH PRESSURE FILTER
The high pressure filter (1, Figure 4-1) filters oil for
the steering and brake circuits.
If the filter element becomes restricted, a warning
indicator located in the cab, on the overhead display
is activated at 40 psi (276 kPa) and oil will bypass the
element at 50 psi (345 kPa).

STEERING/BRAKE PUMP

The Steering/Brake pump (2, Figure 4-1) is mounted
on the rear of the tandem hoist pump. This pump
supplies oil to both the brake system and steering
system. Figure 4-8 shows the location of various
steering pump components. Refer to Figure 4-13 for
a hydraulic circuit schematic of the pump with
unloader and compensator.
FIGURE 4-8. STEERING / BRAKE PUMP
1. Accumulator Connec-
tion
2. Pressure Compensator
Adjuster
3. Unloader Adjuster
Steering Circuit
4. Stroke Adjuster
5. Outlet Port
6. GP2 Port
7. GPA Port
L4-13