thiosulfate is equivalent to 4.0 ppm of oxygen absorption.
(5) The results obtained by the foregoing testing procedures
shall be multiplies by a correction factor determined as follows:
Air shall be diffused into 14 L 0.5 cubic feet or less of
distilled water at 75 mm 3 inches depth for a period of two hours
in which the barometric pressure and water temperature remain
constant. D.O. determinations shall then be made on samples from
the water by the Axide Modification of the Iodometric Method, as
described in AWWA EWW, using sodium thiosulfate solution the same
as used in the tube rating test. The D.O. thus obtained, in ppm,
divided into the solubility of oxygen in ppm in water, for the
barometric pressure and water temperature which were obtained 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 measures taken and three sample tubes shall again be
selected and tested. This procedure shall be followed 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 produced 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.
(7) All accepted tubes shall be suitably marked or stamped by the
manufacturer. Tubes not bearing the rating marks will not be
approved for installation.
b.
Permeability for Porous Plastic Tube Diffusers: The permeability
rate 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 0.09 square meter 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
21.1 degrees C 70 degrees F. Detailed test requirements are 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) Tubes showing permeability ratings outside the specified
range will be rejected. Each tube within the specified range
shall be plainly marked with its permeability rating to the nearest
5 L/s per square meter 1.0 cfm per square foot.
(3) The permeability rating apparatus shall consist essentially
of a container for testing the tubes individually, a meter with a
large easily read scale for measuring the flow of air to the tube,
SECTION 11375N
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