for the two hour test period, shall constitute the correction
factor. The solubility of oxygen in the water shall be that as
indicated for fresh water by AWWA EWW for the particular condition
of barometric pressure and water temperature.
(6) If the results of the oxygen absorption test are
satisfactory, the production of tube diffusers may be started. If
the tubes tested fail to meet the oxygen absorption
specifications, details of manufacture shall be altered or other
corrective measure taken and three sample tubes shall again be
selected and tested. This procedure shall be repeated until the
proper porous structure is obtained to meet the specifications.
After production of tubes has begun, three tubes selected at
random from each tube lot procured for the contract shall again be
tested for the oxygen absorption rating. Should any one of these
samples fail to meet the specifications, additional tubes of the
same tube lot represented by the samples, selected as directed by
the [Contracting Officer] [Contractor Quality Control
representative] shall be submitted for a check test. If any one
of the check samples fails to meet the specifications, the entire
lot of tubes represented by the samples shall be rejected.
b.
Physical Properties Tests: All tubes to be furnished shall be
tested for physical dimensions, shape and bonding characteristics.
Testing frames, maximum and minimum dimension gages and squares
shall be provided by the manufacturer. All tubes with dimensions
outside the specified range, with appreciable warping of surface
showing cracks, soft spots, chipping or other defects, or not free
from adhering foreign material, dirt, oil and clogging material
will be rejected. All tubes shall be tested to a 95 percent
confidence level sampling plan. Tubes actually tested shall have
their ratings so marked upon them. All tubes shall be marked and
include the acceptance mark of the supplier.
c.
Permeability for Porous Ceramic Tube Diffusers: The permeability
rating shall be the number of L/s cfm of free air, at 21.1 degrees
C 70 degrees F and 10 to 25 percent relative humidity, which will
pass through 300 mm square one square foot of tube area, to the
atmosphere under a differential pressure equivalent to 50 mm two
inches of water below the tube when the tube is tested dry at 21
degrees C 70 degrees F.
Detail requirements for the apparatus shall be as follows:
(1) Free air shall be interpreted to mean air at an absolute
pressure equal to the barometric pressure at the time of testing.
(2)
All tubes furnished shall be individually inspected and rated.
(3) The permeability rating apparatus shall consist essentially
of a container for testing the tubes individually; meter with a
large easily read scale for measuring the flow of air to the tube,
pressure gage for indicating the pressure at the tube; recording
thermometers for the test 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 container shall be arranged to
distribute the air uniformly through the tube from the air inlet;
SECTION 11375N
Page 87
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