minutes. These samples shall be immediately tested for oxygen
absorption. The oxygen absorption rate for a 40-minute period, in
which the indicated rate in any 10-minute interval does not vary
more than 10 percent from the average, shall be the oxygen
absorption rating of the clamps.
(3) No oxygen absorption rating tests shall be made when the
uncovered sodium sulfite in the solution in the tank is lower than
300 ppm.
(4) The oxygen absorption rating shall be determined by measuring
the rate of conversion of sodium sulfite to sodium sulfate due to
the oxygen absorption taking place in the solution. This is done
by taking 50 cc samples of the solution at intervals and adding to
each sample such a fixed amount of acidified iodine solution so
that there is always iodine in excess of the amount required to
neutralize the sulfite. The change in sulfite concentration shall
be determined by measuring the change in the excess iodine for
each interval. This shall be done by titrating the excess iodine
with N/40 sodium thiosulfate. For a 50 cc sample of the solution,
a titration difference of 1.0 cc of sodium 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 foot or less of
distilled water at 75 mm 3 inches depth for a period of two hours
during which the barometric pressure and water temperature remain
constant. D.O. determination shall then be made on samples from
the water by the Axide Modifications 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 temperatures which shall be 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 nozzle diffusers may be started.
If the nozzles tested fail to meet the oxygen absorption
specifications, details of manufacture shall be altered and other
corrective measure taken and three sample nozzles shall again be
selected and tested. This procedure shall be followed until the
proper structure is obtained to meet the specifications. After
production of nozzles has begun, three nozzles selected at random
from each nozzle lot produced for this contract shall again be
tested for the oxygen absorption rating. Should any one of these
samples fail to meet the specifications, additional nozzles of the
same nozzle 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 nozzles represented by the samples shall be rejected.
(7) All accepted nozzles shall be suitably marked or stamped by
the manufacturer. Nozzles not bearing the rating mark will not be
approved for installation.
SECTION 11375N
Page 93
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