Steamers and High Pressure Water Supply.
The following is from The Fireman of London: The value of a steam fire engine in a town where there exists what is usually called a good hydrant pressure is not by any means universally understood, although by the patient practice of explaining it over and over again we have probably done, or at least have tried to do, something to promote a correct appreciation of it. But still the question comes to us with regularity from new inquirers. What is the use of a steam fire engine to us when we have a pressure of a hundred and twenty pounds per square inch in our water mains?
If we are discussing this question verbally, we usually inquire whether this very sufficient and satisfactory pressure is found in all parts of the town under discussion, and as a rule we discover that it exists at one point only, the lowest of course in the place. And it also usually appears that this is the highest pressure available at that part under any circumstances.
There are very few large towns in this or any other country in which a steam fire engine is not a necessity, if only for occasional use. The favored exceptions are those cities in which a high pressure is universally distributed, where the mains are of ample capacity throughout, and which contain novety high or large buildings in which anything approaching a conflagration is to be apprehended. In such a town there would always be an ample quantity of water af an ample pressure for all possible requirements. The mere possession of water at high pressure is not enough if the pressure cannot be maintained, whatever quantity it may become necessary to use. Take the case of a very large nre in a town which is well provided with water for all usual requirements. The fire breaks out in the day time. There is first a large quantity of water being drawn off all along the line of pipes between the pumping station or reservoir and the hydrant for domestic and trade purposes. In spite of this, however, when the first contingent of firemen drives up, the hydrant first opened gives a splendid jet, which is not appreciably diminished when another stream is put on the lire. If the flames could be extinguished by these, all would be well; but they cannot, and as hydrant after hydrant is opened in the neighborhood, the quantity of water thrown and consequently the force and power of each stream are sensibly diminished.
It is here that the value of a steam fire engine in such a town arises. By sacrificing the pressure which is being obtained by the use of a working size of nozzle upon hose attached direct to the hydrant, and delivering from the main into a dam, a much larger quantity is obtained from each hydrant. This quantity, picked up by the steamer and discharged again through the hose at a high pressure, becomes a powerful instead of a feeble stream, as it must remain if it is only one of a large number coming from the hydrants direct.
In towns like Manchester and Birmingham, where there are excellent systems of water supply, the steam fire engines are very seldom used. But they are there all the same, and their presence is a necessity. For months together, perhaps, the hydrant streams are able to answer every call upon them. I hen comes a big fire at which many streams are necessary, and the unassisted hydrant pressure is incompetent to meet the demand. The mains then are asked merely for quantity, and the steam fire engines furnish the force.
Of course it might be necessary to use so many streams that even by the aid of steamers satisfactory fire streams could not be thrown. Such a case was discussed in the first article in our number for July last. When it occurs in any district the absolute necessity of larger mains in that locality is amply demonstrated. No place is properly served with water in which it is not possible to get as many streams of an inch and a quarter diameter to work as would be required for the subduing of (he largest lire that could arise in that part. What we desire to point out is that such a deficiency may exist even in localities where there is a pressure of 150 pounds to the square inch or more. There must be high pressure, not only under small draughts, but also when a large quantity is needed.
It is not necessary to enlarge upon the value of steamers in the higher and the outlying parts of a town where the pressure is good enough only in the lower or the central districts ; or (or the purpose of utilizing the wafer in rivers or canals, which is obvious, as Malvolio observed, to any formal capacity.