(8) Each day during the testing of a batch of tubes, one set of
master tubes shall be given a check rating in the permeability
apparatus, (1) at the start, (2) whenever testing conditions
change, and (3) at intervals of not more than four hours. The
variation of the apparent rating from the true rating of the
master tubes shall then be applied as a correction factor to the
apparent rating of all tubes testing during the subsequent period
in order to determine the correct rating to be marked on each.
Where the master tubes show different correction factors, the
correction for the master tube nearest the permeability to the
tube being tested shall be used.
(9) Because the master meter reading for each tube tested will be
the rate for the tube area exposed in the test box, that reading
shall be corrected to a rating based upon 0.09 square meter one
square foot of tube area.
(10) The master tubes shall be guarded against moisture, dirt or
anything that might affect their rating. Only one set of master
tubes shall be used at a time, and the duplicate set shall be
stored in a dry, safe place. The set of master tubes in use shall
be kept in the testing room and placed with the tubes to be tested
in order that they may assume the same conditions as the tubes to
be tested before a check rating is made.
2.19.3
Coarse Bubble Diffusers
2.19.3.1
Non-porous Nozzle Diffuser Tests
Nonporous nozzle diffusers shall be subjected to the following tests:
a.
Oxygen Absorption for Non-Porous Nozzle Diffusers: Prior to
starting production of nozzle diffusers, the manufacturer shall
furnish three samples of the type to be furnished for
installation. The sample nozzles 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
nozzle. 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 nozzle to be rated for oxygen absorption shall
be clamped to the nozzle 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 nozzle attached
shall then be lowered to the tank bottom for the rating test. With
air diffusing from the nozzle at 3.78 L/s 8 cfm, measured as air at
99.3 kPa 14.4 psi absolute pressure and 15.5 degrees C 60 degrees
F, samples of the solution shall be taken every 10 minutes for 40
SECTION 11375N
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