Rotary Actuator; Theory Of Operation; Required Tools - JLG 1200SJP Service Maintenance Manual

SECTION 4 - BOOM & PLATFORM

4.14 ROTARY ACTUATOR

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 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 pressure is applied, the piston is dis-
placed axially within the housing - similar to the operation of a
hydraulic cylinder - while the splines cause the shaft to rotate.
When the control valve is closed, oil is trapped inside the actu-
ator, preventing piston movement and locking the shaft in
position.
Bars indicate starting positions
of piston and shaft. Arrows indi-
cate direction they will rotate.
The housing with integral ring
gear remains stationary.
The shaft is supported radially by the large upper radial bear-
ing 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.
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As fluid pressure is applied, the
piston is displaced axially while
the helical gearing causes the
piston and shaft to rotate simul-
taneously. The double helix
design compounds rotation:
shaft rotation is about twice that
of the piston.
– JLG Lift –

Required Tools

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 outline
troubled 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 - removal of end cap and manual rotation of
shaft.
7. Rubber mallet- removal and installation of shaft and pis-
ton 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 screw-
driver. 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 preference.
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