JLG 680S, Service And Maintenance Manual

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SECTION 5 - BASIC HYDRAULICS INFORMATION & SCHEMATICS
5-46 3121234
5.4 START UP PROCEDURES
Start Up After Overhaul or Replacement of
Components
PRE-FILL OF BOTH THE DRIVE AND FUNCTION PUMP
Machine without oil cooler: When filling the oil tank, fill it to
the very top of the tank. This will give enough head pressure
from the tank to gravity fill the case on both pumps. The
excess oil will be used to fill the cylinders during start up. The
top case port on the outside of the drive pump has a 3/4 in. tee
fitting. Remove the cap from the end of the tee. You should
see oil in 1-2 minutes, tighten up the cap. The drive pump case
is done. Next, go the function pump, using a 3/8 in. allen
wrench remove the plug on the inside of the pump next to the
turn-table side sheet. When oil flows out of the pump, 2-3 min-
utes, re-install the plug. Both pumps are pre-filled. Not doing
this causes the pumps to start dry, and reduces the efficiency
of the pump and can cause premature failure.
Machine with oil cooler: When filling the oil tank, fill it to the
very top of the tank. This will help give enough head pressure
from the tank to gravity fill the case on both pumps. The top
case port on the outside of the pump has a 3/4 in. tee fitting.
Remove the cap from the center of the tee. You should see oil
in 1-2 minutes. If not, depending on hose routing, the drive
pump may not gravity feed. Oil has to flow through the oil
cooler to get to the pump. Hose up an external hand pump to
this tee fitting, and give it about six pumps after it has started
pumping oil. This should be sufficient. Install the cap back
onto the tee fitting. The drive pump is done. Next, go the func-
tion pump, using a 3/8 in. allen wrench remove the plug on
the inside of the pump next to the turn-table side sheet. When
oil flows out of the pump, 2-3 minutes, re-install the plug. Both
pumps are pre-filled. Not doing this causes the pumps to start
dry, and reduces the efficiency of the pump and can cause pre-
mature failure.
PURGING OF THE FUNCTION PUMP SUCTION HOSE.
Large pockets of air get trapped in this line and must be
removed at low pressure. Head pressure from the tank is not
enough. Here are three methods of purging the air from the
hose at low pressure.
1. At the main control valve, remove the 3/4 in. hose from
port “P1” and remove the 1 in. hose from port “T” by
using a 12-16 connector, connect them together. Start
the machine and let it run for approx. 10 seconds. Shut
off the machine, remove the 12-16 adapter and re-hose.
2. Remove the 3/4 in. hose from port “P1” and hold it into a
5 gallon bucket and start the machine. The air should
purge very quickly, (seconds). Shut off the machine and
re-hose.
3. Remove the 3/4 in. hose from port “P1”, using a #12 male
union add approx. 30 in. of 3/4 in. hose to it. Remove the
return filter cap at the top of the tank, lift out the ele-
ment making sure the canister stays in the tank. Hold
the hose end down in the canister and start the machine
and let it run approx. 10 seconds. Re-install the filter and
re-hose the machine.
NOTE: If using a shop vac to create suction on the oil tank while
doing maintenance, both steps “1” and “2” will need done.
NOTE: If installing a new drive pump, step “1” will need done.
NOTE: If installing a new function pump, step “1” and “2” will need
done.
NOTE: If installing a new function pump and the suction hose is
capped without draining a lot of oil out of the hose, which
creates a large air void, step “2” will not need to be done.
NOTE: When operating a function such as Lift Up, if the function
pump makes a loud noise and the lift up stops and starts,
that is a sign of cavitation, air going through the pump at
high pressure. This will in a short time destroy the pump
and contaminate the entire system. Make sure all suction
hoses are tight and free of leaks at the tank and pump. A
suction hose does not leak when the engine is running, it
will allow air to be drawn into the pump causing cavita-
tion. After the machine is shut down, then you will see a
very slow leak.