Checking Pre-Charge - JLG sky trak mmv Service Manual

Hydraulic System
9.13.3

Checking Pre-Charge

Gas Leaks
1. If an external leak is suspected, apply soapy water to
the gas valve and the seams of the gas end cap. If
bubbles form, the accumulator has to be replaced.
2. If an internal leak is suspected, check for foaming oil
in the hydraulic oil reservoir and/or no accumulator
action. If any of these signs are evident, the
accumulator has to be replaced.
Checking Accumulator Recharge Pressure and Nitro-
gen Pre-Charge
Note: This procedure will require the assistance of a
second person to read the pressure gauge on the engine
side of the vehicle.
1. Park the vehicle on a firm, level surface, fully retract
all hydraulic cylinders, ground the attachment (if
any), place the travel select lever in [N] NEUTRAL,
place the neutral lock lever in the [N] NEUTRAL
LOCK position, engage the park brake switch and
shut the engine OFF.
2. With the engine OFF, pump the brake pedal
repeatedly until the accumulators are completely
discharged. This will allow the free floating piston to
bottom against the hydraulic end cap in each
accumulator. ALL stored pressure should now be
removed from the brake accumulator system.
3. Unlatch and open the engine cover.
4. Locate the diagnostic test nipple (1) on the
accumulator charge valve (2) in the "SW" port.
Attach a 5000 psi (348 bar) pressure gauge to the
test nipple.
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. Shut the engine OFF.
8. Slowly pump the service brake pedal while closely
watching the pressure gauge.
9.138
9. 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 700 psi (48 bar).
10. If either of these readings are outside the
recommended ranges, the accumulator charge valve
may need repair or replacement. Section 9.12.10,
Accumulator Charge Valve .
11. If the nitrogen charge pressure is not correct Section
9.13.2, Pre-Charging Accumulator .
2
12. Remove the pressure gauge from the test nipple and
reinstall the protective rubber cap.
13. Close and latch the engine cover.
1
MM4450
Model MMV Rev. 12/04