irement which
must be met.

LONGITUDINAL DRUM CONSTRUCTION--The heating surface of this type of
boiler is made up of a drum or drums, depending upon the width of the
boiler extending longitudinally over the other pressure parts. To the
drum or drums there are connected through cross boxes at either end the
sections, which are made up of headers and tubes. At the lower end of
the sections there is a mud drum extending entirely across the setting
and connected to all sections. The connections between all parts are by
short lengths of tubes expanded into bored seats.

[Illustration: Forged-steel Drumhead with Manhole Plate in Position]

The drums are of three sheets, of such thickness as to give the required
factor of safety under the maximum pressure for which the boiler is
constructed. The circular seams are ordinarily single lap riveted though
these may be double lap riveted to meet certain requirements of pressure
or of specifications. The longitudinal seams are properly proportioned
butt and strap or lap riveted joints dependent upon the pressure for
which the boilers are built. Where butt strap joints are used the straps
are bent to the proper radius in an hydraulic press. The courses are
built independently to template and are assembled by an hydraulic
forcing press. All riveted holes are punched one-quarter inch smaller
than the size of rivets as driven and are reamed to full size after the
plates are assembled. All rivets are driven by hydraulic pressure and
held until black.

[Illustration: Forged-steel Drumhead Interior]

The drumheads are hydraulic forged at a single heat, the manhole opening
and stiffening ring being forged in position. Flat raised seats for
water column and feed connections are formed in the forging.

All heads are provided with manholes, the edges of which are turned
true. The manhole plates are of forged steel and turned to fit manhole
opening. These plates are held in position by forged-steel guards and
bolts.

The drum nozzles are of forged steel, faced, and fitted with taper
thread stud bolts.

[Illustration: Forged-steel Drum Nozzle]

Cross boxes by means of which the sections are attached to the drums,
are of forged steel, made from a single sheet.

Where two or more drums are used in one boiler they are connected by a
cross pipe having a flanged outlet for the steam connection.

[Illustration: Forged-steel Cross Box]

The sections are built of 4-inch hot finished seamle