2.9.13.6
Weighing Mechanism
Enclose in a dusttight compartment. Construct of cold rolled steel for
minimum deflection, warp, and twist. Pivot points shall be self-aligning
with hardened double bearing surfaces. Weighing mechanism shall be
complete with weight lever, tare adjustment, and compensator, [with design
subject to approval by the Contracting Officer], and scale shall be
guaranteed to weigh coal accurately within 0.25 percent.
2.9.13.7
Scale Weigh Hopper
Construct scale weigh hopper and discharge gate of not less than 14 gage
stainless steel plate, continuously welded and stiffened with angle irons.
Weigh hopper shall be of such design and construction to ensure clean
discharge.
2.9.13.8
Controls
Provide controls, except those required for weigh hopper discharge,
prewired and located in a NEMA [12] [3] dusttight enclosure. Provide
circuit breaker interlocked with electrical panel door. Control circuits
shall be two wire nominal 120 volt systems obtained by using an isolation
transformer with one side grounded and wired to a single terminal block
which shall be included in the electrical panel. Segregate circuits of
different voltage levels. Controls shall include large, oiltight,
industrial type pushbuttons for use as "start-stop," "test," and "dump"
switches mounted on the scale body adjacent to the electrical panel.
2.9.13.9
Counters
Mount a mechanical type coal counter on the scale body. Counter shall be
rugged, reliable, with heavy duty register and designed so that double
counting is impossible. [A remote motor operated counter shall be
furnished located on the coal handling control panel in the control room.
Counter shall be designed so that double counting is impossible.] [Provide
a contact closure for sending a pulse signal of each weigh hopper discharge
to the operator control console.]
2.9.13.10
Scale Inlet
Scale inlet shall contain coal gate with opening not less than 457 by 457
mm or 406 by 508 mm 18 by 18 inches or 16 by 20 inches along with a
dusttight all metal slip joint constructed of not less than 4.76 mm 3/16
inch thick steel plate. Slip joint shall be of split construction to allow
for installation after coal scale is in place. Design slip joint to allow
necessary flexibility to take care of deflection of [bunker] [silo] outlet
due to varying load and temperature variations without imposing load on the
scale. Provide rope packing or other resilient gasket material to make
slip joint completely dusttight.
2.9.13.11
Scale Outlet Hopper
Not less than 6 mm 1/4 inch thick 410 stainless steel plate of capacity not
less than 227 kg 500 pounds and 13 mm 1/2 inch thick steel plate flanges.
2.9.14
Stoker Hopper Extension
Dusttight and bolted to hopper furnished with stokers.
Construct hopper
SECTION 15501N
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