JLG 460SJ Service Manual - Manual (Page 277)

SECTION 4 - BOOM & PLATFORM
3120895 – JLG Lift – 4-13
4.5 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.