Owing to the contracted diameter of fire hose, the flow of the water is retarded; the loss of power due to friction increases directly with the length of the line and nearly as the square of velocity. In other words, if the loss due to a given flow be 12 pounds for 100 feet of hose, then 24 pounds will be required to maintain the same rate through an additional 100 feet. To double the velocity will require four times the pressure, or 48 pounds for 100 feet and 96 pounds for 200 feet.
From this brief explanation, it must be plain that the capacity of any engine is diminished as the length of the line of hose is increased.
For this reason, the greater the lift the smaller the stream that can be thrown effectively, and the size of nozzle used should depend upon the height the water is draughted, reducing it one-eighth inch for every five feet above a lift of ten feet. If the engine uses a 11⁄4-inch nozzle for ordinary work, it will answer for any lift up to 10 feet. If water has to be draughted 15 feet, a 11⁄8-inch nozzle should be used; if 20 feet, 1-inch; and if 25 feet, 7⁄8-inch.
Never start a fire unless one full gauge cock of water appears in the boiler.
The suction basket or strainer should always be attached when draughting water, and every precaution taken to insure tight connections in the suction. The basket must be kept well under the surface, to avoid clogging if the water be foul.
When the supply is taken from a hydrant, the valve should be fully turned on; if opened before water is wanted through the hose the discharge gates on the pumps must be closed. Unless the pressure is excessive, the hydrant is usually permitted to remain open while the steamer is attached, the discharge during temporary stops being controlled by the pump gates.
The apparatus should always be halted, or placed at a proper point, with reference to the source of the water supply. When attached to a hydrant or plug, do not run the engine faster than the water will flow to supply the pump, and if the supply is not sufficient to allow the pump to work to its full capacity, avoid using too large nozzles.
The safety of life and property is very often dependent upon the skill and good judgment of the engineer, and as the maximum effect of such apparatus is generally required at the most critical time and under the most exciting circumstances, it is important that the endeavor by constant and persistent practice to acquire that confidence and proficiency that will insure a correct and decisive action in all matters pertaining to the management of the machine.
From three-fourths to one inch of water should be indicated in the glass gauge, except when there is a heater attached to the engine, then from four to five inches should be carried. The bottom of the glass tube being on a line with the crown-sheet, when one inch of water shows in the tube, the water-line in the boiler is then one inch above the crown-sheet.