JLG 450A_AJ Series II Service Manual - Manual (Page 219)

SECTION 4 - BOOM & PLATFORM
3121290 – JLG Lift – 4-7
4.2 ROTARY ACTUATOR
Theory of Operation
The L20 Series rotary actuator converts linear piston motion to
shaft rotation. Each actuator is composed of a housing with
integrated gear teeth (01) and only two moving parts: the cen-
tral shaft with integrated bearing tube and mounting flange
(02), and the annular piston sleeve (03). Helical spline teeth
machined on the shaft engage matching splines on inside
diameter of piston. Outside diameter of piston carries a sec-
ond set of splines, of opposite hand, which engage with
matching splines in the housing.
As hydraulic pressure is applied, piston is displaced axially in
the housing - similar to a hydraulic cylinder - while splines
cause shaft to rotate. When control valve is closed, oil is
trapped inside actuator, preventing piston movement and
locking shaft in position.
Shaft is supported radially by large upper radial bearing and
lower radial bearing. Axially, shaft is separated from housing
by upper and lower thrust washers. End cap is adjusted for
axial clearance and locked in position by set screws or pins.
Required Tools
Basic tools required for assembly and disassembly of the actu-
ator and their intended functions are as follows:
1. Flashlight - helps examine timing marks, component
failure, and overall condition.
2. Felt Marker - match mark timing marks and outline trou-
bled areas.
3. Allen wrench - removal of port plugs and set screws.
4. Box knife - removal of seals.
5. Seal tool - assembly and disassembly of seals and wear
guides.
6. Pry bar - end cap removal and manual rotation of shaft.
7. Rubber mallet - removal and installation of shaft and
piston sleeve assembly.
8. Nylon drift - installation of piston sleeve
9. End cap dowel pins - removal and installation of end cap
(sold with Helac seal kit).
The seal tool is a customized flat-head screwdriver. To make this
tool, heat flat end with a torch and bend to a slight radius in a
vice. Round off sharp edges with a grinder.
Bars indicate starting positions
of piston and shaft. Arrows indi-
cate rotation direction. Housing
with integral ring gear remains
stationary.
Shaft glands, bearings, and end
cap are not shown for clarity.
As fluid pressure is applied, pis-
ton is displaced axially while
helical gearing causes piston
and shaft to rotate simultane-
ously.
D o u b l e h e l i x d e s i g n c o m -
pounds rotation: shaft rotation is
about twice of piston.