JLG 680S Service Manual - Manual (Page 258)

SECTION 5 - HYDRAULICS
5-18 – JLG Lift – 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 you enough head
pressure from the tank to gravity fill the case on both
pumps. The excess oil will be used to fill the cylinders dur-
ing start up. The top case port on the outside of the drive
pump has a ¾” 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” 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 premature failure.
Machine with oil cooler: When filling the oil tank, fill it to
the very top of the tank. This will help give you 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 ¾” 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
(6) 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 function pump, using a
3/8” 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 premature 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 (3) methods of purging the air from
the hose at low pressure.
1. At the main control valve, remove the ¾ inch hose
from port “P1”, remove the 1 inch hose from port
“T”. 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 ¾” 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 ¾” hose from port “P1”, using a #12
male union add approx. 30” of ¾” hose to it.
Remove the return filter cap at the top of the tank, lift
out the element 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.