*Size prescribed below.
Section 10. The Pneumatic Apparatus shall be constructed as shown in Figure 2, and shall consist of a two-inch vertical pipe P ten feet long hermetically closed at the top and having a small water outlet cock C at the bottom. An air exhaust pump E and a vacuum gauge G shall be connected with this pipe at a convenient height from the ground as shown. A two-inch trap testing branch B provided with a quick opening valve V shall be connected with the main pipe just below the pump connection. Also a back air connection A for coupling on the back air pipes Figure 3.
The trap to be tested is secured to the branch pipe in the same manner as in the hydraulic apparatus. The strain to be applied is obtained by closing the valve V and pumping the air out of the pipe until the vacuum gauge indicates five inches of vacuum. This strain is now applied to the trap by opening the valve V which forces the air through the trap seat and breaks the vacuum in the main pipe. A repetition of this action ten times without refilling the trap constitutes the standard test required. Any trap maintaining a water seal one Xth of an inch deep after this test shall be accepted as an effective non-syphoning trap.*
Section 11. Back Air Pipes will be allowed as protection for traps against syphonage when they stand the same test connected with the trap which is applied as standard to non-syphoning traps. For test purposes vent pipes made of thin tubing and connected up as shown in Figure 3 shall be employed. A sufficient number of pipe lengths and bends shall be used in the test to produce an amount of air friction corresponding with that of the vent pipe to be used in the actual building, and for purposes of Easy Calculation the surface friction of a one and one-half inch pipe shall that of a two-inch pipe, and y times that of a three-inch pipe, and z times that of a four-inch pipe, and w times that of a five-inch pipe, and in the same proportion for larger pipes. Hence where a certain length of one and one-half inch pipe is found to reach the limit which will protect the trap in the standard test, x, y, z, or w times, this length will form the limit when the vent pipes are increased in area accordingly. The friction of a quarter bend shall be taken as equivalent to x* feet of pipe of the same bore as that of the bend.
To couple on at A be taken as x times*
Figs. 1 & 2
*The pneumatic apparatus permits of further comparative tests in the relative efficiency of different kinds of traps, or systems of trapping, by permitting the application of higher degrees of vacuum, and it also provides an accurate means of testing the comparative efficiency of non-syphoning traps with syphon traps protected by mechanical vents or by back air pipes either new or partially clogged with sediment.
In tall buildings the size of the back vent pipe shall be increased for each stony by an amount determined by the friction tests for each such additional length.
The back air pipe used in the test shall be applied at the opening A on the branch pipe B. Different lengths are obtained by opening or shutting the gates G1, G2, G3, G4, etc.
Back air pipes shall be nowhere less than one and one-half inches in diameter and nowhere less than the diameter of the trap they serve.
Back air pipes shall not be accepted as protection against syphonage for kitchen or pantry sink traps nor for any trap regularly used for discharging greasy waste.
All back air pipes shall be provided with clean-out screw caps at every 90 degree bend on vertical runs for the periodical removal of rust flakes or other deposits, and these caps shall be opened and the deposits removed as often as they accumulate in quantity sufficient to reduce the bore 01 the pipe by one-third of its area, whereby its effectiveness in protecting the trap from syphonage may be destroyed.
Suitable provision shall be made to prevent the upper end of the back air pipe from being obstructed by frost or snow in cold weather.
The Joints of all back air pipes shall be tested for tightness as provided for in Sections 34 to 40.
Section 12. Mechanical Vents. Where mechanical vents are accepted as meeting the requirements of this section, suitable provision shall be made to ensure their mechanical parts against being rendered inoperative by rust, sediment or other cause.
*These proportions to be calculated and substituted for the algebraic expressions here given.
Section 13. Protection of Water Closet Trap Seals. A shallow seal non-syphoning or refilling trap shall be accepted as a suitable back air vent for a water closet syphon trap provided the trap shall have proved acceptable under the standard test, and provided it shall be placed near enough to the water closet trap to be effective, and provided the depth of seal of such non-syphoning trap shall not exceed one quarter the depth of seal of the water closet trap, so that the water seal of the non-syphoning or refilling trap shall yield to the syphoning strain and admit air to break the vacuum before the deep seal of the water closet trap is affected.
Section 14. Evaporation. The test for resistance to evaporation shall consist in connecting up the trap with the testing apparatus and closing the valve V" and allowing the trap to stand for thirty days without refilling. The trap shall be accepted as fulfilling the requirements when it shall be found to have lost less than one-xth of an inch of its seal through evaporation in this time.
When the trap is a syphon trap or intended to be protected by a back air pipe, the test apparatus of back air pipes (Figure 3) shall be applied and a current of air shall be induced through the back air pipes by means of a suction pump or fan at a speed of one foot a second as measured by an anemometer. If less than one-xth of an inch of the trap seal is removed by evaporation in thirty days under this test. the trap and its back air pipe shall be accepted in this respect.