Methods of Waste Prevention
Various Means Employed to Prevent Loss in the Pumping Plant and the System of Distribution
IT goes without saying that no system of water distribution can ever attain to an efficiency of 100 per cent. In fact, recent war time investigations showed that many systems were not averaging much better than fifty per cent, and some actually fell below this. Taking into consideration the fact that every step in the process of impounding and distributing a supply of water involves an outlay, it will be apparent that there are as many sources of loss possible as there are stages in this process. For example, in a system employing reservoirs, there may be seepage at the latter, frequently running into substantial volumes daily; leakage between the reservoir and the pumps, excessive slip at the latter, fuel and heat waste at the power plant, leakage in distributing mains and laterals and last, but far from least, waste at the consumer’s outlet. In smaller systems employing no reservoirs, but drawing their supply from deep wells, some of these sources of loss would be eliminated while the use of electrically driven pumps would cut out the losses incidental to the usual large steam operated plant.
Power Plant Losses
I he latter are in the majority, however, and in the aggregate the loss and waste must run into almost incredible figures if all of the power plants in this country were being run on anything like as low a percentage of efficiency as those which were investigated last year. Where a plant operates twenty-four hours a day and seven days a week, even a slight falling off in efficiency involves a substantial loss in the course of a year. Most losses of this character are not apparent upon casual inspection, but they are operating just as steadily as the plant itself. Chief among these are the practice of hand firing the boilers that is still commonly followed in most water works plants, whereas industrial plants have to a large extent adopted mechanical stokers of one type or another. By eliminating the necessity for frequently opening the fire doors and by steady and regular stoking of the fuel only as fast as it can be burned most efficiently, an installation of mechanical stokers will save enough coal in a single year of operation to more than offset its first cost. This, in addition to the saving in labor.
Another substantial source of loss is to be found in the sooting up of flues and deposits of scale in the boiler tubes, both of which are responsible for heavy heat losses. Industrial plants have a great advantage in this respect in that week-end shut-downs afford frequent opportunities for keeping up boiler efficiency, but with a sufficient duplication of units to allow for this as well as emergency operation, the water works plant is placed in an even better position to maintain a high standard of efficiency.
Attempts at fuel economy in the pumping plant while water is allowed to leak out of the mains is on a par with the classic saving at the spigot and wasting at the bung, since a comparatively small number of leaks in the distributing mains would far more than offset the highest degree of economy that could be maintained in the boiler room. Water main losses may be due either to settling of the ground below the pipes at certain points, or to lack of pressure-relieving valves at intervals in the lines. In both cases, the caulking is apt to be forced out of the joints, either by adjoining lengths of the main settling to a sharp angle with each other or by reason of the excess pressure generated by “water hammer” when gate valves are closed quickly and no means of relieving this high pressure is provided.
The location of the ground may be such that these leaks are not readily detected. Starting small, the flow cuts an underground channel for itself and either does not come to the surface at all, or rises at a point so far distant from the main that its connection with the latter is never suspected. Instances of the former kind are to be found where a leak in the main is close to a sewer and the water runs off in constantly increasing volume without the leak giving any indication at the surface. Some years ago, when New York City was threatened with a water famine, a pitometer survey brought to light many unsuspected leaks of this character that had been running for years, wasting many millions of gallons per day. In one case, a single leak in a main was responsible for the loss of three million gallons every twenty-four hours and it had been running so long that it had come to be commonly regarded in the neighborhood as an underground stream. This particular main was located within thirty feet of the river bank on made ground, the street having originally been filled in over a swamp, so that the leak readily cut a channel to the river and discharged into it for years.
An example of the second type of leak was the basis of a law suit in a small city directly adjoining New York. A piece of property on the outskirts of the town changed hands, one of the inducements to the sale being a very attractive spring of bubbling clear water on a low part of the land. The mains of the local water company ran along the highway bordering the most elevated part of the tract. Water became very scarce the following summer and, after making a Pitometer survey of its distribution svstem, the water company stopped a good-sized leak in that particular main, beside a number of others. Whereupon the spring promptly dried up and the buyer quite as promptly sued the seller of the property, alleging that the chief inducement to its purchase had been the aforesaid “spring.” Due to the lay of the ground, the water leaking from the main ran down hill under the surface for almost a hundred yeards before it broke through. It had been running for years and its connection with the water mains had never been suspected. The mains may also be responsible for a pressure loss through the accumulation of sediment by years of use. This greatly reduces the effective diameter of the pipe and causes a drop in the pressure so great as to be dangerous for fire-fighting purposes. Where no sedimentation basins are employed, this accumulation in the mains will be comparatively rapid, but it cannot be avoided even where filtration and sedimentation are both practised since anything but distilled water always carries a certain percentage of solids and organic matter in suspension and this is deposited in proportion as the flow through the main is rapid or the reverse. As the demand for water falls to a minimum during several hours of each night, this deposit of sediment takes place in all mains so that it has been nothing unusual to find instances in which the deposit had reduced the free opening to onefourth or even less of the effective diameter of the pipe.
The Manchester, X. 11., Water Works Department recently bought a carload of lead, 30,000 pounds at 5 1/2 cents a pound, for which the price is now six cents. The department proposes extension of a 20-inch main this season.