where the digging point is accessible only to a vertically
Caution: Do not attempt to raise the
operated bucket.
boom by means of the boom hoist
lines if the boom tip is below the level
b. Load Limits. Refer to paragraph 1-4 for load
of the ground which supports the
limits before starting operation.
carrier. The angle of pull on the
c. Positioning the Carrier. Back the carrier to the
boom will be such that the boom may
work site so that most of the work will be performed over
collapse before it can be pulled into
the rear of the carrier. Dumping or unloading should be
the operating position.
done over the sides of the carrier, if possible. Set the
carrier brakes, and extend and set the outriggers (fig. 2-
2-16. Clamshell Operation
d. Operating Cycle. The clamshell operating cycle
a. General. The model M320T2 truck crane, with
consists of four steps; filling the clam bucket (closing);
the crane boom and a clam bucket installed and reeved
raising the load bucket, swinging and dumping. The
for clamshell operation, is used to handle material which
boom angle position is set before beginning operations in
is relatively loose or soft and must be accurately dumped
the same manner as for the crane (fig. 2-36). Start the
at a higher level than would be possible with a shovel
crane engine (para 2-11 ) and operate the clamshell as
attachment. The clamshell attachment is used widely for
shown on figure 2-37.
loading and unloading loose material from ships and
open freight .cars, and for digging deep' pits or shafts
2-37
