JLG 600SC_660SJC Service Manual - Manual (Page 133)

SECTION 4 - BOOM & PLATFORM
3121607 – JLG Lift – 4-31
Testing Actuator
If equipment is available, test actuator on a hydraulic test
bench. Breakaway pressure — the pressure at which the shaft
begins to rotate — should be approximately 400 psi (28 bar).
Cycle actuator at least 25 times at 3000 psi (210 bar) pressure.
After 25 rotations, increase pressure to 4500 psi (315 bar).
Check for leaks and cracks. Perform test again at end of rota-
tion in the opposite direction.
Testing Actuator for Internal LeakS
If actuator is equipped with a counterbalance valve, plug valve
ports, connect hydraulic lines to housing ports. Bleed all air
from actuator (see Installation and Bleeding). Rotate shaft to
end of rotation at 3000 psi (210 bar) and maintain pressure.
Remove hydraulic line from non-pressurized side.
Continuous oil flow from open housing port indicates internal
leakage across the piston. Replace line and rotate shaft to end
of rotation in opposite direction. Repeat test procedure out-
lined above for other port. If there is an internal leak, disassem-
ble, inspect, and repair.
Installation and Bleeding
AFTER INSTALLING ACTUATOR, IT IS IMPORTANT THAT ALL SAFETY DEVICES
SUCH AS TIE RODS OR SAFETY CABLES ARE PROPERLY REATTACHED.
To purge air from hydraulic lines, connect them together to
create a closed loop and pump hydraulic fluid through them.
Review hydraulic schematic to determine which hydraulic
lines to connect. The linear feet and inside diameter of hydrau-
lic supply lines together with pump capacity determine
amount of pumping time required to fully purge the hydraulic
system.
Bleeding may be necessary if excessive backlash is exhibited
after actuator is connected to hydraulic system. The following
steps are recommended when a minimum of two gal (8L) is
purged.
1. Connect a 3/16" inside diameter x 5/16" outside diame-
ter x 5 foot clear, vinyl drain tube to each of the two
bleed nipples. Secure with hose clamps. Place vinyl
tubes in a clean 5-gallon container to collect purged oil.
2. Oil can be returned to reservoir after procedure is com-
pleted.
Figure 4-28. Actuator Bleed Ports
3. With an operator in the platform, open both bleed nip-
ples 1/4 turn. Hydraulically rotate platform to end of
rotation (clockwise or counterclockwise), and maintain
hydraulic pressure. Oil with small air bubbles will be
seen flowing through the tubes. Allow 1/2 gallon of fluid
to be purged from actuator.
4. Keep fittings open and rotate platform in opposite
direction to end position. Maintain hydraulic pressure
until an additional 1/4 gallon of fluid is pumped into the
container.
5. Repeat steps 2 & 3. After last 1/2 gallon is purged, close
both bleed nipples before rotating away from end posi-
tion.