material to seal the shaft openings. Stuffing boxes shall be designed such
that the packing can be adjusted or removed from the outside of the duct,
without removing or disturbing the bearings or the linkage. Adjusting
nuts, washers, and bolts shall be 316 stainless steel conforming to UNS
S31600 (.03 to .08C) and shall incorporate a self-locking design, such that
vibrations in the damper unit will not cause backing out of the bolts.
Bearings shall be permanently lubricated, self-aligning type. Bearings
shall be mounted outboard of the damper unit and any insulation and
lagging, in such a manner that leaking packing will not cause the bearing
to become contaminated with fly ash. Each bearing and bearing mount shall
be designed to withstand three times the stress transmitted from the load
on the blades plus the operator output torque. Linkage system shall be
located outside of the damper unit. Linkage system shall be fully
adjustable to compensate for thermal expansion of the frame. Parts with
threaded connections for adjustment shall be carbon steel. Provide lock
nuts on the adjustable linkage to positively hold the linkage after
adjustment. Design shall be such that each individual blade can be
adjusted. Clevis arms shall be pinned or bolted to the stub shaft. Arms
shall be keyed to the shaft for easy removal. Clevis arm shall be carbon
steel and linkage pins or bolts shall be 304 stainless steel conforming to
UNS S30400 (.03 to .08C). Pins or bolts shall incorporate a self-locking
design, such that operation or vibration of the unit will not cause
loosening of the connections. Linkage system, including connections, shall
be designed to withstand three times the stress transmitted from the load
on the blades plus the operator output torque. Linkage system shall have
provisions for locking with a heavy-duty padlock in such a manner that the
damper cannot be operated until the padlock is removed. Sealing strips
shall conform to ASTM B 443. Strips shall be bolted into place with bolts
and nuts fabricated of the same alloy as the strips. Connection shall be
self-locking to prevent loosening of the connection. Seal strips shall be
of a suitable length to enable easy replacement in the event of damage or
failure. Sealing strips are not required for induced draft fan dampers.
Louver dampers shall be either parallel or opposed blade. Blades shall be
air-foil type, of rigid structural design. Blade skin and through shaft
shall be compatible material for expansion and contraction. Blade shall be
connected to through shaft with self-locking bolts or pins. Louver dampers
except the induced draft fan inlet control dampers and dampers in vertical
ducts shall be designed for staged closing. Operation of the blade shall
be such that blades close, except the bottom blade. When the upper blades
have closed, then the bottom blade will close. Provide two operators on the
linkage system, one to operate the top blades, and one to operate the
bottom blade. Design of the linkage shall be such that the number of
blades operated by each operator may be changed with relative ease. To
prevent ash buildup at bottom of hopper, install purge air system.
2.11.3.3
Poppet Dampers
Poppet dampers shall be vertically operating, with pneumatic operators,
adjustable speed and stroke, shaft packing glands, replaceable seal plates,
and machined steel seating cylinder and guide shaft. The dampers shall be
equipped so they can be mechanically locked in a closed position to protect
service personnel. Poppet damper shafts shall be out of the dirty gas
stream wherever possible. Shafts exposed to the flue gases shall be
provided with shaft seals. Poppet dampers shall be a minimum of 99.5
percent gas tight.
2.11.3.4
Guillotine Dampers
Guillotine dampers shall be bottom-entering dampers in paragraph entitled
SECTION 15864N
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