THE USE OF THREE INCH HOSE
This discussion was written for the convention of the International Association of Fire Engi neers, held at Washington, D. C., on October 10, 1907. It formed topic II, as follows:
“Thre-inch hose is used in many progressive fire departments—Why? Three-inch hose is stupidly misused in some progressive departments. — Why? Three-inch hose is sometimes equiped with 2’/,Hnch couplings.—Again, why?”
As we all know, the reason why 3-in. hose is used, instead of 2½-in., is to do away with part of the loss of pressure caused by the friction of the water in passing through 2j4-in. hose. The reason why it is misused in some departments is because the principles in regard to its proper use are misunderstood. When 3-in. hose is fitted with i’A-in. couplings, it shows that the facts and principles are properly understood and are correctly applied. When is the proper time to bring 3-in. hose into play? Certainly not when streams of only moderate strength are wanted, nor when the 2½-in. hose provides a sufficiently good channel to lead the water to the nozzle. Threeinch hose should be used to replace 2-in. whenever the smaller hose is inadequate to perform the service required in an efficient manner. What is a ‘‘sufficiently good channel” for practical fire service? When outside streams are called for, the channel should consist of hose short enough or large enough to let an ample supply of water reach the nozzle at from 40 to 60 lbs. pressure, without either overstraining the hose near the engine or making the engine hold such a high water-pressure that it* speed will be seriously reduced. How does the friction in 3-in. hose compare with the friction in 2½-⅛. hose? The pressure lost in friction depends principally upon the amount of water flowing through the hose. But, if we assume that the same amount of water is flowing in two lines—one of 3-in. hose and the other of 2½-in.—the pressure lost in friction in the 3-in. line will be practically only one-half as much as in the 2-in. line. Another way of saying this is: I hat 3-in. hose will carry water to a nozzle twice as far from the engine for the same fare that is paid to 2n. hose for taking it half the distance. For example: Let us say that we want to get a good stiff 1 ⅜-in. stream with 50 IDS. pressure at the nozzle. Also, let us say that our old engine is in no better condition than it ought to be, so that we cannot reasonably expect more than 160 lbs. water-pressure at the engine. As we want 50 lbs. left in the, water at the nozzle, this leaves only no lbs. to spend in hose-friction. How far will no lbs. carry us when using the stream just mentioned? Experience shows that the necessary amount of water -nearly 400 gals, per minute—will have to give up more than 18 lbs. of its pressure in passing through each 50 ft. length of ordinary 2 hose. Consequently, no lbs. pressure will drive thi* amount of water through 300 ft. of this hose, and there will then be left at the nozzle only 50 lbs. out of the 160 lbs. which the water had on leaving the engine. By using 3-in. hose, the effective radius is doubled, so that a stream having 50 lbs. at the nozzle can be played through a 600jt. line under the conditions above mentioned. 1 bis is one of the chief advantages to be gained by using 3-in. hose. When a large engine is playing two streams, or when still larger nozzles and higher nozzle pressures are wanted, the advantage gained by using 3-in. hose is still more marked. But a limit is very soon reached, when even 3-in. hose, in its turn, becomes inadequate. The next improvement over 3-in. hose is to Siamese two j’/lines or Siamese a 3-in. with a 2½-⅛. line. The two lines of 2½-⅛. hose combined practically cut down the friction of a single 2j/£-in. line to one-quarter, and, consequently, cut the friction loss in a 3-in. line about in halves, just as in the previous case, the change from 3in. hose to two siamesed lines of 2j4-in. hose means doubling the effective radius, so that a 50lb. stream from a ifjj-in. nozzle could be played, if necessary, at a distance of 1,200 ft. from the engine without calling for water-pressure at the engine of much more than 160 lbs., simply by siamesing two lines of 2j/2-in. hose. When a first-size engine is attempting to play two large streams, it sometimes happens that the extra pressure caused by using fairly long lints of 2’/2-in. hose is just sufficient fo slow the engine down, so that neither of the streams is as power f.il as desired. Here, again, is a situation which calls for 3-in. hose. This larger size hose would cut down the friction and allow the engine to speed up, with the result that the streams would gain materially in force. How is 3-in. hose misused in actual practice? In a variety of ways. One of the commonest is by having that 3-in. hose equiped with 3-in. couplings, so that the couplings are not interchangeable with these on the standard 2]/ hose and on the regular equipment of play-pipes, Deluge sets, cellar-pipes, etc. When 3-in. couplings are used, a makeshift lot of reducers and enlargers has to be carried, in order to make connection with 2 hose or appliances. Three-inch hose is also sometimes misused, as shown in the accompanying illustrations, which were taken from real life. Figure 1 shows an attempt to use a 2-in. nozzle on the end of a 1,000-ft. line of 3in. hose. The engine held the water-pressure well alxive 200 lbs. The stream at the nozzle was so feeble that it could not go across the street, without using crutches. Before the test began, the writer said that two lines should be siamesed, if a decent 2-in. stream through such a long line were wanted. Figure 2 shows the result of siamesing two 500-ft. lines into a 2-in. nozzle. Then the writer was asked how large a nozzle could be used effectively at the end of the 1,000-ft. single line. The answer was that a l$4-in. nozzle was about the limit, as the pressure on any larger nozzle would fall below 30 lbs. Figure 3 show’s the in. stream. The nozzle – pressure agreed exactly with the predicted pressure of 35 lbs. Figure 4 shows a 1¾-⅛. stream through the same line of hose. The stiffness of this stream may well be contrasted with that shown in figure i. In all similar tests, as well as in actual fireservice, it is not difficult to predict approximately what the nozzle-pressure will be. The principles of hydraulics are absolute, and will not change simply to help us weak mortals to put out paltry fires. Rather shall we have to change our method of attack, when our intended scheme runs counter to hydraulic laws. Another obvious misuse of 3-in. hose occurs, whenever an attempt is made to use such unwieldly and heavy lines for inside work, particularly if the lines have to be shifted frequently from place to place. To carry a line of 3-in. hose when full of water up over a 40 or 50-ft. ladder is another sample of misuse. Those of us who have tried this experiment over an ice-covered aerial are apt to have some very definite ideas on the subject. For any such use as this, one or two lengths of 2}4-in. hose should be added to the nozzel end of the line of 3-in. hose. But does not the use of 2^2-in. hose couplings add materially to the friction in 3-in. hose and thereby noticeably reduce the pressure at the nozzle? No. The 2½-⅛. couplings, if properly tapered, do not add materially to the frictionlosses in a line of 3-in. hose. Can this be proved? Yes. John R. Freeman and Dexter Bracklett, both eminent hydraulic engineers, made careful tests, which showed that, even when the 2½-⅛. couplings were intentionally poorly designed, the increase in friction-losses was negligible—only a fraction of a pound. But has any practical test been made to convince a practical man? Yes. In 1899 the present writer, then hydraulic engineer in the Boston fire department, was instructed to make a study of the proper use of 3-in. hose. As a result, most of the 3-in. couplings were replaced by 2½-⅛. couplings, and the use of 3-in. hose was increased. Two years later, however, our late lamented associate, Chief Cheswell, took command of the department, and, like the gentleman from Missouri, he wanted to be “shown.” lie would not take any such’seeming paradox on mere say-so. The writer, at about ten minutes’ notice, had to give a hurried demonstration. Two lengths of 3-in. hose, with a i>£-in. nozzle, were attached to one of the engines. Streams of varying strength were played. The pressures at the nozzles were observed bv means of a nozzlcguage, and the pressers at the engine were observed and recorded at the same time. Then a 2^2-in. sleeve, with souare corners, was inserted at the middle coupling in the line, and the pressures at both nozzle and engine were observed again. Although several dozen observations were taken bv both Chief Cheswell and the writer, we both failed to find that the presence of the sleeve increased the friction-losses in the line. Perhaps, if more time had been allowed to make a very delicate and accurate test, a loss of a small fracwith the means at hand, we could read the gauges tion of a pound might have been discovered. But, only to the nearest half-pound, and, in no case, was the difference as much as half a pound. Needless to say, Chief Cheswell was convinced. The writer was only strengthened in his firm belief that different sizes of hose-couplings are entirely unnecessary evils, without any shadow of justification. Can practical tests to show the advantage of 3-in. hose and of siamesed lines be easily made by any fire department? Yes. The simplest test is to lay two long lines of 2j^-in. hose and one line of 3-in. hose all side by side, and use a single 1 ⅜-in. nozzle. First Siamese the two 2½in. lines together. Attach the nozzle and see what pressure at the engine will be needed to give 50 lbs. pressure at the nozzle. The nozzle-pressure can be most conveniently ascertained by using a fire-stream gauge of suitable design—it would hardly be modest of the writer to state what particular make of gauge is the best for the purpose. Having noted the pressure at the engine, with the two lines siamesed, attach the same nozzle to the 3-in. line and make a second run, bringing the nozzle-pressure againup to 50 lbs., as in the first run. This makes sure that the engine is pumping just the same amount of water as before. The pressure at the engine will be considerably greater than before. The difference between the first and the second pressures at the engine shows the saving made by the use of siamesed lines over the use of a single 3-in. line. Finally, attach the same ij^-in. nozzle to one of the single lines of 2½-⅛. hose and increase the pressure until 50 lbs. is again shown on the guage at the nozzle. The additional pressure required at the engine will he very evident. In fact, if the line is oyer 600 ft in, length, the chances are that the engine will be unable to put up a pressure of 50 lbs. at the nozzle at all. This demonstration is sufficiently practical to convince any board of commissioners of the advantage to be gained through the use of 3-in. hose and siamesed lines. It also shows incidentally one of the many ways in which a fire-stream gauge may be of practical use in a fire department. N. B.—The results of any test showing the relative saving in friction-losses in 3-in. over 2j^-in. hose may not agree accurately with the figures given in the earlier part of this discussion. It should be remembered that no two pieces of hose will cause exactly the same loss through friction, and even a single piece under differing conditions will show different results. The figures given above are fairly average results taken from hundreds of observations made by the writer both at actual fires and tests. In some cases, the 3-in. hose showed a saving of very much more than fifty per cent, of the friction, while, in other cases, the saving was slightly less than that amount.