The Value of the Steamer.
An English journal, Hydraulics, asks: “How is it that steam fire engines are used in towns where there is a pressure in the mains equal to that which can be obtained from a steamer? For instance, in such towns as Manchester and Liverpool, where, as it is well known, there is constant high pressure service in the street pipes sufficient for putting out fires?” To this question our London contemporary, The Fireman, makes the following reply :
“The towns which have a pressure equal to that which a steam fire engine would furnish are very few indeed. A much larger number have a pressure which is amply sufficient for all ordinary fires ; but when a large conflagration has to be dealt with (and there is no certain method of preventing large conflagrations anywhere) the quantity of water furnished by the hydrants is not nearly sufficient for the purpose. For example, in order to pass only 150 gallons per minute through 200 feet of hose, and to throw this quantity to a height of sixty feet only, a head at the reservoir of 210 feet above the point at which the hydrant is situated is required ; even then the quantity would only be delivered at the necessary pressure if the diameter of the pipes were large enough, and there were no draughts being taken from the mains for domestic and other uses. A few comparatively small domestic draughts practically interferes very seriously with the pressure, as Sir Joseph Bazalgette proved to the Board of Works many years ago. While, therefore, the mains furnish an adequate supply for small fires, they will not give sufficient to deal with large bodies of flame, and it becomes necessary to sacrifice the pressure as far as the gravitation service is concerned, and obtain as large a quantity of water as possible at the ground level, and to pick it up there by the steamer, and obtain from the latter the force which is to throw the water upon the fire. You will see the great difference between this operation and the throwing of a direct stream from the hydrants, when we mention that a pressure of 100 feet head at the hydrant which through 200 feet of hose would give only about 150 gallons per minute to a height of thirty-five feet would deliver into a canvas dam as much as 1000 gallons per minute, the whole of which quantity would be available for the steam fire engine suction. This, picked up by steamers, could be thrown through a similar length of hose to the above to a height of 140 feet instead of thirty-five feet as with the unassisted pressure. Another reason for the employment of steamers in towns having a good gravitation pressure is, that it is impossible to rely solely upon water company’s pressure unless that pressure is distributed in all parts of a town. This is very seldom the case, especially in new neighborhoods, where pipes are usually of insufficient capacity to allow more than one moderately good stream to be obtained. And, thirdly, it is always desirable not to depend on one means of fire extinction, because a great fire might occur just when the water company’s mains were not fully charged, owing to accident, drought, etc. A steamer takes its supply from a river, pool, etc., in fact, utilizes water from any source.”