3-16
The operator can hear the accumulators charge. If the accumulators charge frequently without
depressing the brake pedal, the brake unloading valve, accumulators, or brake hoses may be
leaking. If no leaks can be found, check accumulator pre-charge pressure. If pre-charge pres-
sure is adequate, it may be necessary to repair or replace the brake unloading valve. If the ac-
cumulators do not charge, take a long time to charge, or cycle very rapidly, it may be necessary
to repair or replace the brake unloading valve.
Relief pressure for the brake circuit is located in the unloading valve. It is set at 2925 psi (202
bar) at the factory. The relief pressure cannot be adjusted. The relief pressure can be checked
by installing a pressure gauge at the P port of the valve.
Brake Modulating Valve
: Directly connected to the brake pedal. This valve sends pressure
and flow to the brake calipers when the brake pedal is depressed. Lubricate the pedal hinges
with a silicone lubricant. No other routine maintenance is required. If the brakes do not apply
and the Brake Malfunction Light is not illuminated, the brake modulating valve may need repair
or replacement. If the brakes do not fully release and the brake calipers are functioning proper-
ly, the brake modulating valve may need repair or replacement.
Brake Accumulators
: Mounted under the floorboard of the operator’s compartment. The
brake accumulators store hydraulic oil under pressure for use at the brake calipers. They are
bladder-type accumulators, and require a pre-charge pressure in the gas bladder. The brake
accumulator pre-charge pressure must be maintained on a monthly basis as follows:
1. Set park brake or put machine on outriggers. Turn off engine.
2. Pump the brake pedal several times to discharge stored oil pressure.
3. Remove protective cap from the accumulator.
4. Connect a pressure gauge to the accumulator valve stem.
W A R N I N G
Accumulator pressure gauges will not detect accumulator pre-charge pressure if im-
properly used. Carefully review pressure gauge and pre-charging instructions included
with commercially available gauge kits.
5. Measure accumulator gas pre-charge pressure. Nominal pressure is 1000 ± 100 psi (69 ± 6.8
bar).
W A R N I N G
NEVER use shop air or oxygen to pre-charge accumulators. ONLY use inert dry nitrogen
(N
2
) gas. Failure to use proper gas can cause accumulator damage or failure, leading to
property damage, injury, or death.
6. If necessary, add only dry nitrogen gas (N
2
).
7. Disconnect all gauges. Replace valve caps.
If the accumulators are unable to hold a pre-charge pressure, or if the brakes fail to operate
properly, they may be damaged. The accumulator pressures should cycle between 2175 psi
(150 bar) and 2675 psi (184 bar). Accumulator bladder replacement instructions and accumula-
tor replacement instructions ship with replacement parts. In the event that instructions are not
included, contact BMC. Proper procedure is necessary to prevent damage or premature failure
of replacement parts.
To Next Page
Loading...
