The drum (fig. 4-49) winds and unwinds the drive
system cables to advance or retract the grab, based on
directional rotation of the hydraulic motor. The drum is
directly coupled to the hydraulic motor and is geared to
the screw of the traverse carriage.
The traverse carriage prevents the advance and
retract cables from becoming crossed and tangled on the
drum when the retraction engine is operating. The
traverse carriage, which is driven by a screw, slides on
the tracks mounted on the retraction engine frame. (See
fig. 4-50.) The screw is driven through gearing from the
drum. The rotation of the drum causes one set of cables
to wind onto the drum and the other set of cables to
unwind from the drum. When the drum and screw
rotate, the carriage moves along the retraction engine
frame, guiding the cables onto and off of the drum.
Retraction Engine Manifold
The retraction engine manifold (fig. 4-51) is
mounted on the retraction engine frame and provides
Figure 4-49.—Rotary retraction engine.]
4-39
