JLG M450 ANSI Service Manual - Manual (Page 125)

SECTION 4 - BOOM & PLATFORM
3121127 – JLG Lift – 4-13
4.13 HELAC ROTARY ACTUATOR
Theory Of Operation
The 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 com-
posed of a housing with integrated gear teeth (01) and
only two moving parts: the central 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 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 pres-
sure is applied, the piston is displaced axially within the
housing -similar to the operation of a hydraulic cylinder
while the splines cause the shaft to rotate. When the con-
trol valve is closed, oil is trapped inside the actuator, pre-
venting piston movement and locking the shaft in position.
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.
NOTE: Bars indicate starting positions of piston and shaft.
Arrows indicate direction they will rotate. The hous-
ing with integral ring gear remains stationary.
As fluid pressure is applied, the piston is displaced
axially while the helical gearing causes the piston
and shaft to rotate simultaneously. The double helix
design compounds rotation: shaft rotation is about
twice that of the piston.
Tools Required for Assembly/Disassembly
Upon assembly and disassembly of the actuator there
are basic tools required. The tools and their
intended functions are as follows:
1. Flashlight- helps examine timing marks, component
failure and overall condition.
2. Felt Marker- match mark the timing marks and out-
line troubled areas.
3. Allen wrench- removal of port plugs and setscrews.
4. Box knife- removal of seals.
5. Seal tool- assembly and disassembly of seals and
wear guides.
6. Pry bar- removal of end cap 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 merely a customized standard flat head-
screwdriver. To make this tool you will need to heat the flat
end with a torch. Secure the heated end of the screwdriver
in a vice and physically bend the heated end to a slight
radius. Once the radius is achieved round off all sharp
edges of the heated end by using a grinder. There may be
some slight modifications for your own personal prefer-
ence.