RESULTS OF CLEANING WATER MAINS AT PITTSBURG.
The question of cleaning water mains is one in which those having charge of waterworks management are becoming more and more interested. There is not a city in the United States where a waterworks system has been installed for any length of time, that the great mains do not become inadequate for supplying the demand. In some cases, of course, it is due to the growth of the city being far more rapid than was originally calculated upon. Then, the only solution is the one of relaying—i. e., replacing the too small mains with those of a larger carrying capacity, however. The more frequent cases, are where the mains become clogged with tubercular formation or mud, so that their carrying capacity is so reduced as to be insufficient to meet the demand. There are two solutions to this last case—namely, to take up these mains and replace them with new, or to clean them. As cleaning is by far the cheaper operation, this seems to be the reasonable course to pursue, provided the mains themselves are in good condition, aside from this stoppage by tubercular formation or mud. The city of Pittsburg first took up the cleaning of mains about two years ago. The pressure in part of our Hazelwood territory for five or six years back kept gradually decreasing. This territory was supplied by an 8-in. supply-main, about fourteen years old, passing through Schenley park. At the end of this main, the pressure was 34 lb. below the theoretical static head. A thorough survey was made of this main by means of pitometers; but no leaks could be discovered. In making these pitometer tests, it was found that a coating of scale on the inside of the pipe greatly reduced the diameter. It was decided, therefore, to clean this main (some 3,200 ft.) as an experiment, and the contract for cleaning was awarded to the National Water Main Cleaning company, of New York city. The scale taken from this pipe was carefully measured, and from this it was estimated that a coating of .32 in. covered the entire last section of cleaned pipe, varying from to 3/4-in. at different locations. In the cleaning, two pieces of lead, caused by defective yarning, were removed, one of these weighing 45 lb. The results of the cleaning operation were as follows:
There were 3,264 lin. ft. of this main cleaned, the discharge being taken by means of a 6-in. Crest meter. As the city had trouble in the dropping of the pressure in the Oakland district, where the mains were mostly old, it was decided to clean some of these this year. This work was taken up about a month ago, and is now nearly completed. The following are the results of these operations on the 6-in main on Bouquet street, Fifth avenue, South :
The velocity and discharge in this case, as in all other tests of mains cleaned this year, were determined by means of pitometers. The coefficient of velocity is the ratio between the average velocity and the maximum velocity of the pipe. The following are the results of cleaning a 6-in. main on Bouquet street, Frazier street, Fast :
There were 1,800 lin. ft. of this line cleaned. A 6-in. main on Ward street, Frazier East, was cleaned, with the following results:
There were 864 lin. ft. of this line cleaned. This main was comparatively new, and the inside was in fairly good condition, as will be seen by the coefficient of velocity being 79 per cent, before cleaning. This would account for the smaller percentage of increase as compared to other mains cleaned. A test was made in connection with the cleaning of a 4-in. main on Meyran avenue, from Fifth avenue South, to determine the relation of the percentage of increase to the length cleaned. The flow was determined through the full length—1,834 feet—before cleaning. The pipe was then broken, and at 905 1/2 ft., the flow was determined. It was then broken at 477 1/2 ft., and the flow determined. After cleaning, the same process was followed out in the reverse order. The following are the results with the 1,834 ft. Before After
Another interesting test was made line on Craft avenue, before and after cleaning this line having been laid about 40 years. At some places in this line, the opening was nearly stopped up by tuberculation.
As will be seen from these tests, the percentage of increase varies from 64 per cent, to 564 per cent. This determination of percentage of increase, simply tends to tell us how dirty the pipes were, when cleaned. What would be a better result is to obtain the percentage of maximum carrying capacity of the mains after cleaning. At present, to obtain the theoretical maximum carrying capacity, we have about twelve different formulas, which can nearly all be reduced to the wcllknown formula V-CR S, known as the Chczy formula, in which R-Hydraulic mean Radi D Area ft.
us = and S = slope of water surface, 4-Cir. ft.
or lost head per foot. The only trouble we then have, is with C, the coefficient, which varies so under different conditions and experiments, which have been tabulated by different wellknown experimenters, that engineers are at a loss what to use for this variable. For instance, in a 6-in. pipe we can find this coefficient varying from 70 to 107, all taken from results of well conducted experiments. This coefficient being so variable, it is almost impossible to say at present that mains shall be cleaned to 95 per cent, or any other per cent, of their maximum carrying capacity which is rendered variable by the use of Coef. C. Why would it not be better, then, as experiments tend to show that the cleaning of water pipe is a saving operation, for the water company or municipality to install a hatch-box, for cleaning, when pipes are first laid, so that the interior surfaces of pipes can be examined from time to time and also, to put in a pitometcr-tap. and test these lines when first laid, in order to determine the maximum carrying capacity’, and then, when pipes are cleaned, to bring them back to a reasonable percentage of maximum carrying capacity, as found in the new pipes—say, for the first year?