(11) All diffuser tubes furnished under this contract shall have
sufficient strength to carry a load equivalent to a 4.50 m 15 foot
depth of water, with a safety factor of not less than 1.7, and to
withstand the stresses of reasonable handling and shipping.
2.19.2.2
Porous Plastic Tube Diffuser Tests
Porous plastic tube diffusers shall be subjected to the following tests:
a.
Oxygen Absorption for Porous Plastic Tube Diffusers: Prior to
starting production of plastic tube diffusers, the manufacturer
shall furnish three sample tubes of the type to be furnished for
installation. The sample tubes shall be tested for oxygen
absorption by the manufacturer and shall be selected at random by
him. Detailed test requirements are as follows:
(1) The oxygen absorption rating test shall be made in a tank.
The tank shall be 1.05 m 3 feet 6 inches long by 475 mm one foot 7
inches wide, holding approximately 473 L 125 gallons. The tank
shall be filled with tap water, at 22.22 degrees C 72 degrees F,
to a depth of 900 mm 3 feet 0 inches, covering the top of the
diffuser tube. Sodium sulfite to the amount of 1,200 ppm and 66
Baume scale sulfuric acid to the amount of 50 ppm, shall be
dissolved in the water. The sulfite shall be put into solution by
removing some of the water from the tank, dissolving the sulfite
in this water and then pouring it back into the tank while air is
being diffused into the solution in the tank to insure a thorough
mixing.
(2) Each diffuser tube to be rated for oxygen absorption shall be
submerged in tap water for one hour or more just prior to the
rating test. The tube shall then be clamped to the tube holder,
lowered into the tank to just below the solution, and inspected
with the air diffusing. Any leaks along the gasket shall be
eliminated by additional tightening of the clamps. The container
with tube attached shall then be lowered to the tank bottom for
the rating test. With air diffusing from the tube at 0.59 L/s
1.25 cfm, measured as air at 99.3 kPa 14.4 psi absolute pressure
and 15.55 degrees C 60 degrees F, samples of the solution shall be
taken every 10 minutes for 40 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 tube.
(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 shall be
done by taking 50 cc samples of the solution at intervals and
adding to each sample such a fixed amount of acidified iodine
solution 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 with N/40 sodium thiosulfate. For a 50 cc sample of
the solution, a titration difference of 1.0 cc of sodium
SECTION 11375N
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