JLG M600 Service Manual - Manual (Page 122)

SECTION 4 - BOOM & PLATFORM
4-12 – JLG Lift – 3121813
If the actuator is not equipped with grease fittings, the
thrust bearings (20) are coated with good grease before
sliding on the shaft and end cap. The shaft is installed by
again aligning the proper punched timing marks. Tempo-
rarily taping the threaded portion of the shaft will help
installation past the shaft seals (masking tape works well).
Apply anti-seize to threaded and surrounding areas of the
end caps. Also, depending on the size of the actuator
(60K and larger), the end cap may need to be installed
with the actuator in a vertical position.
The end cap (5) is torqued to 60-400 ft-lb (84-560 Nm)
depending on the actuator size, such that the actuator
begins rotation at approximately 100 psi (6.9 bar) pres-
sure. The shaft flange cannot be rotated by hand; the
combined backdrive efficiency and friction prevent man-
ual rotation. If the end cap is torqued too high, the actua-
tor may require as much as 300 psi (20.7 bar) to rotate. If
the end cap is not torqued high enough, shaft axial motion
and radial backlash will result. The end cap must be
secured against the shaft by tightening cap screws (7), or
by installing axial setscrews, depending on the
model. Apply hydraulic pressure and check for breakaway
pressure and shaft axial motion.
To test for leakage, pressurize Port P2 to 3000 psi (206.8
bar). No oil should seep from Port P1 or from around end
cap (5). Repeat test by pressurizing Port P1 and check for
leakage out of Port P2, around shaft flange (2B), and from
ring gear pin welds.
4.4 PLATFORM ROTATOR (S/N
0300130810 TO PRESENT)
Theory of Operation
The L20 Series rotary actuator is a simple mechanism that
uses the sliding spline operating concept to convert linear
piston motion into powerful shaft rotation. Each actuator is
composed of a housing with integrated gear teeth (01)
and only two moving parts: the central shaft with inte-
grated bearing tube and mounting flange (02), and the
annular piston sleeve (03). Helical spline teeth machined
on the shaft engage matching splines on the in- side
diameter of the piston. The outside diameter of the piston
carries a second set of splines, of opposite hand, which
engage with matching splines in the housing. As hydraulic
pressure is applied, the piston is displaced axially within
the housing - similar to the operation of a hydraulic cylin-
der - while the splines cause the shaft to rotate. When the
control valve is closed, oil is trapped inside the actuator,
preventing piston movement and locking the shaft in posi-
tion.
The shaft is supported radially by the large upper radial
bearing and the lower radial bearing. Axially, the shaft is
separated from the housing by the upper and lower thrust
washers. The end cap is adjusted for axial clearance and
locked in position by set screws or pins.
Bars indicate starting posi-
tions of piston and shaft.
Arrows indicate direction they
will rotate. The housing with
integral ring gear remains sta-
tionary. As fluid pressure is applied,
the piston is displaced axially
while the he lical gearing
causes the piston and shaft to
rotate simultaneously. The
double helix design com-
pounds rotation: shaft rota-
tion is about twice that of the
piston.