Service Manual Instruction Manual

SECTION 4 - BOOM & PLATFORM
4-8 – JLG Lift – 3121616
4.4 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 composed of a housing with integrated gear
teeth (1) and only two moving parts: the central shaft with
integrated bearing tube and mounting flange (2), and the
annular piston sleeve (3). Helical spline teeth machined on the
shaft engage matching splines on the piston inside diameter.
The piston outside diameter carries a second set of opposite
direction splines which engage with matching splines in the
housing.
Bars indicate starting positions of piston and shaft. Arrows
indicate direction of rotation. The housing with integral ring
gear remains stationary. As fluid pressure is applied, the piston
is displaced axially while helical gearing causes the piston and
shaft to rotate simultaneously. The double helix design com-
pounds rotation: shaft rotation is about twice of the piston.
As hydraulic pressure is applied, piston is displaced axially
within the housing - similar to operation of a hydraulic cylin-
der - while splines cause shaft to rotate. When control valve is
closed, oil is trapped inside the actuator, preventing piston
movement and locking shaft in position. The shaft is sup-
ported radially by the large upper radial bearing and lower
radial bearing.
Required Tools
1. Flashlight - Examine timing marks, component failure,
and overall condition.
2. Felt Marker - Match mark timing marks and outline trou-
bled areas.
3. Allen wrench - Remove 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 - Piston sleeve installation.
9. End cap dowel pins - removal and installation of end cap
(sold with Helac seal kit).
The seal tool is a customized standard flat head screwdriver. To
make this tool, heat flat end with a torch. Secure heated end of
screwdriver in a vice and bend to a slight radius. Once radius is
achieved, round off all sharp edges using a grinder. There may
be some slight modifications for your personal preference.
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