Lull 944E-42 Service Manual - Manual (Page 152)

Hydraulic System
8-36 944E-42
8.7.16 Checking Pre-Charge
a. Gas Leaks
1. If an external leak is suspected, apply soapy water to
the gas valve (10) and the seams of the gas bottle
(11). If bubbles form, the accumulator has to be
replaced.
2. If an internal leak is suspected, check for foaming oil
in the hydraulic reservoir and/or no accumulator
action. If any of these signs are evident, the
accumulator has to be replaced.
b. Checking Accumulator Recharge Pressure and
Nitrogen Pre-Charge
1. Park the machine on a firm, level surface, level the
machine, fully retract the boom, raise the boom, place
the transmission control lever in (N) NEUTRAL,
engage the park brake and shut the engine OFF.
2. With the engine OFF, pump the brake pedal
repeatedly until the accumulators are completely
discharged. ALL stored pressure should now be
removed from the brake accumulator system.
3. Remove the access plate from the cab floor.
4. Locate the test port (12) on the accumulator charge/
secondary function valve in the “SW” port. Attach a
3000 psi (207 bar) pressure gauge to the test port.
5. Start the engine and allow the accumulators to fully
charge. Slowly pump the service brake pedal, while
closely watching the test gauge.
6. Record the lowest pressure observed before the
accumulator recharges. The pressure should be
950 -1200 psi (65 -83 bar). This reading is the
accumulator recharge pressure.
7. Record the highest pressure observed when the
accumulator charge valve shifts and unloads the
pump. This pressure should be 1900 -2100 psi
(131 -145 bar) and is the high limit. If the
accumulator charge valve does not reach the high
limit and continues to load the pump, refer to Section
8.7.17, “Accumulator Charge Troubleshooting,” step
2.
8. If either of these readings are outside the
recommended range, the accumulator charge/
secondary function valve may need repaired or
replaced. Refer to Section 8.7.14, “Accumulators.”
9. Shut engine OFF.
10. Slowly pump the service brake pedal while closely
watching the pressure gauge.
11. Record the lowest pressure observed before the
pressure drops to nearly zero. This reading is the
nitrogen pre-charge of the accumulators. This
pressure should be approximately 450 psi (31 bar). If
there is any doubt about the pressure reading,
proceed to the next step.
12. If the nitrogen charge pressure is not correct, follow
procedures in Section 8.7.16, “Checking Pre-
Charge.”
MU1971
11
10
MU1941
12