As it was inconvenient to watch the working of the drain through the traps, I constructed an instrument called a detector[[1]] to observe the working of the atmosphere in the drain. This instrument, or a gas-pressure gauge, when attached to the drain, will denote by the rising of the liquid the amount of compression in the drain. This, when compared with the quantity of water thrown into it, will give the size and capacity of the drain, and will also indicate any siphoning of traps or leaks which exist in any of the sanitary fittings of the house.
[1]. This instrument with instructions as to reagents can be obtained from E. Cetti, Meteorological Instrument Maker, 36, Brooke Street, Holborn, price 12s. 8d. It is cheaper and more convenient than the pressure-gauge, and registers any pressure during the testing of drains.
The following table will show the amount of gas in every 100 feet of circular pipe or drain, from 4 to 30 inches in diameter, also the amount of water thrown into a trap to produce the necessary pressure of gas to lift the liquid 1 inch in the detector or pressure gauge: the quantity being as near as possible 3⅓ ozs. of water to 1 cubic foot of gas space.
Plate 1.
| Diameter of Circular Pipe or Drain. | Cubic Contents of Gas in each 100 feet length of Drain Pipe or Sewer. | Amount of Water to produce 1 inch rise of Liquid in Detector. | Area of Pipe 1728 = 1 cubic foot. | ||
|---|---|---|---|---|---|
| ins. | cub. ft. | gals. | pts. | ozs. | |
| 4 | 81255 1728 | 0 | 1 | 7 | 12·566 |
| 6 | 191096 1728 | 0 | 4 | 0 | 28·274 |
| 9 | 44308 1728 | 1 | 1 | 2 | 63·617 |
| 12 | 78932 1728 | 2 | 0 | 5 | 113·097 |
| 15 | 1221242 1728 | 3 | 1 | 6 | 176·715 |
| 18 | 1761234 1728 | 4 | 5 | 0 | 254·469 |
| 19 | 1961546 1728 | 5 | 1 | 1 | 283·529 |
| 20 | 218288 1728 | 5 | 5 | 7 | 314·160 |
| 21 | 240913 1728 | 6 | 2 | 1 | 346·361 |
| 22 | 2631695 1728 | 6 | 7 | 0 | 380·133 |
| 23 | 288917 1728 | 7 | 4 | 2 | 415·476 |
| 24 | 314276 1728 | 8 | 1 | 6 | 452·390 |
| 25 | 3401530 1728 | 8 | 7 | 0 | 490·875 |
| 26 | 3681212 1728 | 9 | 4 | 13 | 530·930 |
| 27 | 3971063 1728 | 10 | 2 | 14 | 572·556 |
| 28 | 4271147 1728 | 11 | 1 | 12 | 615·753 |
| 29 | 4581201 1728 | 11 | 7 | 8 | 660·521 |
| 30 | 4901512 1728 | 12 | 6 | 9 | 706·860 |
The method of testing drains and fittings by compression of gas is as follows:—When the drainage plan of a building exists, the work of testing by compression of gas in the drain will be a very simple matter.
Plate 1 shows the drains as laid to a semidetached villa, with two inlets from sinks marked 1, one from bath overflow marked 2, and two from the soil-pipes of closets in the basement and first-floor marked 3. The drain from A to B is a 6-inch stoneware pipe, and its length is 100 feet. The amount of gas in it would be 191096
1728 cubic feet. The branch drains from the other inlets are 4 inches in diameter, and the collected lengths are 50 feet, and the quantity of gas in them would be 4627
1728 cubic feet, giving a total in the whole of the drain of nearly 24 cubic feet.
If the indiarubber pipe to the detector or pressure gauge is placed in either of the traps marked 1, and the glass tube filled with liquid up to the data line, 5 pints of water poured into either of the traps marked 1, will produce a rise of 1 inch in the liquid of the detector, that is if all the drains are clear and joints tight, the drains being stopped off for testing at A.
Should a trap be fixed anywhere between A and B a lesser quantity will be required to lift the liquid, and the position of the trap can be determined by comparing the exact quantity of water used with the capacity or quantity of gas in the drain.