pressure gage for air, and the necessary controlling devices. The
container, or test box, shall be provided with suitable clamping
devices for holding the tube in position and completely sealing
the tube against the passage of air except through the exposed
face. The plate supports and clamping devices shall be so
designed that no less than 0.064 square meter 100 square inches of
the top and bottom of the tube will be exposed for the passage of
air, and the top and bottom areas shall be equal and concentric.
The container shall be arranged to distribute the air uniformly
through the tube from the air inlet; and the inlet shall be not
less than 75 mm 3 inches in diameter.
(4) The meter shall be of the orifice type, of proper size, and
installed in accordance with the recommendation of AGA GMC.
Before tube tests are started, the calibration of the orifice
meter shall be checked with a standard displacement type gas meter
of not less than 31.47 L/s 4,000 cfh capacity which has been
accurately calibrated volumetrically in a manner satisfactory to
the [Contracting Officer] [Contractor Quality Control
representative]. When checking the orifice meter, the inlet of
the standard gas meter shall be connected to an opening in a steel
plate clamped in the test box and the outlet of the gas meter
shall be to the atmosphere. The checking of the orifice meter
shall be done in the presence of the [contracting Officer]
[Contractor Quality Control representative]. When checking the
orifice meter, the inlet of the standard gas meter shall be
connected to an opening in a steel plate clamped in the test box
and the outlet of the gas meter shall be to the atmosphere. The
checking of the orifice meter shall be done in the presence of the
[contracting Officer] [Contractor Quality Control representative].
The calibration of the orifice meter may be checked with an
orifice plate, calibrated as described above, suitably arranged
for clamping into the test box.
(5) The test air supply shall be such as to give a continuous
non-pulsating flow of air with a relative humidity between 10 and
25 percent. A suitable equalizing tank and moisture control
equipment, with recording hygrometer, shall be provided for the
purpose.
(6) Each diffuser tube shall be tested dry for its permeability
rating.
(7) In order to establish correction factors for actual testing
conditions, duplicate sets of reference or "master" tubes shall be
carefully rated at the time the flow meter is calibrated and used
for comparison as hereinafter specified. Each set of master tubes
shall consist of three diffuser tubes with permeability rating of
37.0, 40.0, and 43.0, respectively, for Type A tubes, and 24.0,
26.0 and 28.0, respectively, for Type B tubes. A tolerance of 0.5
plus or minus will be allowed on each permeability rating. The
master tubes shall be rated in the presence of the [Contracting
Officer] [Contractor Quality Control representative] at the
standard temperature of 21.11 degrees C 70 degrees F for the test
air and the plates, with the test air within the specified range
of 10 to 25 percent relative humidity and the barometric pressure
prevailing at the same relative humidity within the specified
range.
SECTION 11375N
Page 91
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