Practical Tests of a Turbine Fire Pump.
Page 11
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By the Captain of a Lancashire Fire Brigade.
It occurs to the writer that a few notes with regard to a number of tests, which he has had the opportunity of carrying out with a turbine fire pump recently, might prove useful if placed on record for the benefit of the readers of THE COMMERCIAL MOTOR.
The pump in question was designed and built to give an output of 900 gallons per minute at 120 lb. pressure. During the first test, this task was per. formed with every satisfaction for a period of three hours and working on a jet of 114 in. bore. This gives the required delivery.
It was then decided to endeavour to ascertain what margin of overload could be obtained by using all the power at our disposal, and it was found that a pressure of 150 lb. could be obtained with the use of the same jet when the engine was going all out. We had during these tests a very useful table of pressures and quantities before us for various sizes of jets. It was found from this that a. 11 in. jet, at 150 lb. pressure, should yield an output of 446 gallons per minute, so, presumably, that was what we were getting.
The next test consisted of an attempt to ascertain what quantity of water we should deliver at a useful working pressure, and we then found that we could maintain a pressure of 80 lb. with a 1 in. and a 1 in. jet working together, when we were using all the available engine power. This gave us the surprising delivery of 733 gallons per minute. On consulting the afore-mentioned tables again, we found that a i in. jet and a 14 in. jet acting together pass practically the same amount of water as six in. jets (in parallel). This performance it would be admitted would make a very good display for a 400-gallon pump at 80 lb. pressure.
it may be useful to tabulate the results.
possible to obtain such a delivery at a similar useful working pressure from a rain pump designed for 400 gallons per minute at 120 lb. pressure. Hence, it would appear that the superiority of the turbine pump for fire purposes is almost incontestable, for, if the necessity arose, it would be possible to put on two or three extra jets when using a turbine, and the latter would respond to the extra demand with only a slightly-reduced pressure. But let us suppose for a moment that a ram pump, designed and built to give 400 gallons per minute at. 120 lb. pressure, and capable of an overload up to 150 lb. pressure, as in the ease of the turbine under consideration, is put to similar tests. The results, if tabulated, would then appear somewhat as follow : — From the above figures, it will be seen that the ram pump is given credit for passing 470 gallons per minute, which, it is suggested, is probably more than it can do.
The limiting factors of a ram pump are, from a constructor's point of view, the capacity of the pump barrels, and the highest speed at which it may be worked smoothly. These limitations set a firm margin to the amount of water which can be delivered, which quantity cannot under any circumstances be exceeded. But the turbine pump knows no such mechanical restrictions. There is little doubt that the turbine with which the above tests were conducted would pump 1000 gallons per minute at about 40 lb. pressure. There should be no attempt to claim that the turbine is as efficient as the ram pump, but that is hardly the question where economy is not of first importance. Surely it is far better to employ a lessefficient pump, but one which has an overload capacity to which it is not easy to set a limit. This is certainly a better proposition than the employment of a type of pump of Which the high efficiency is obvious, but by the use of which a strictly limited output only is obtainable.