3-38
BOOM SEQUENCE
The RT-400 uses a single extension cylinder to extend all three moving stages. The cylinder is
a multi-stage design, and uses a chain system to proportionally extend and retract the second,
third, & fourth stages together.
BOOM CHAIN ADJUSTMENT
Study Illustrations 1,2, and 3 on the following page, to understand the chain adjustment proce-
dure. Proper adjustment is critical at time of boom assembly or scheduled maintenance.
Initial adjustment:
Retract boom completely. The 4
th
stage extension and retraction chains
determine the position of the 4
th
stage, relative to the 3rd stage. As shown in Illustration 1, ½”
(13mm)-clearance must be held between the 4
th
stage tip and 3rd stage tip. To increase this
distance, loosen the retraction adjustment and tighten the extension adjustment. To decrease
this distance, loosen the extension adjustment and tighten the retraction adjustment.
Final adjustment
: Extend boom completely while horizontal, then slightly retract the boom to
let the chains relax. Measure the inside chain drape at the center of the rear 3
rd
stage and 2
nd
stage windows, as shown in Illustration 3. See arrows in the windows for measuring locations.
Measure the outside chains at midspan. Snug the 4
th
stage extension and retraction chains un-
til the chain tightness allows the dimensions of approximately 1” (25mm) and 5” (127mm), as
shown in Illustration 3. Also snug the 3
rd
stage compensation chains to the dimensions of 1 1/8”
(29mm) and 3 7/8” (98mm), as shown. Assure that the drape in each pair of chains is matched
so each chain carries its share of the load. Run boom in and out a few times and recheck all of
the above dimensions. After proper settings attained, retighten the adjustment lock nuts.
The number “3” shown in the small windows on the bottom of the 2nd stage and base boom,
show the adjustment is about midrange. These numbers run from 1 to 6, in 1” (25mm)-
increments. Numbers in these windows are approximate adjustments and cannot be used for
final adjustments. Please note the importance of the dimensions stated above, taken at the
large side windows.
.
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