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New Handy Site On Plumbing
Diameter of the pipe has nothing to do with the static head or pressure; but its relation to the size of the orifice from which the water is to be drawn has much to do with the amount of pressure lost by friction. If a faucet and supply pipe are of the same size and we DOUBLE the size of the pipe, the velocity of the water flowing through it is reduced three-fourths; and friction is, under these conditions, but one-sixteenth what it was in the original size. Furthermore, as in drawing similar amounts of water under the same head through a one-inch and two-inch pipe, the amount of friction surface presented is twice a? great in the one-inch as in the two-inch pipe. The friction in the one-inch can be shown to be 32 times as much as in the two-inch pipe.
By using the formula it is possible to find the approximate theoretical delivery. A liberal percentage must be deducted for friction, based on size, length of pipe and head or pressure.
The two tables, with the rules of how to use them, will be of great value for ready reckoning.
Table No. 1 shows the pressure of water in pounds per square inch for elevations varying in height from 1 foot to 135 feet.
Table No. 2 gives the drop in pressure due to friction in pipes of different diameters for varying rates of flow. The figures given are for pipes 100 feet in height. Frictional resistance in smooth pipes having a constant flow of water through them is proportional to the length of pipe. That is, if the friction causes a drop in pressure of 4.07 pounds per square inch in a 11/4 inch pipe, 100 feet long, which is discharging 20 gallons per minute, it will cause a drop of 4.07 X2 equals 8.14 pounds in a pipe 200 feet long; or 4.07:2 equals 2.03 pounds in a 50 feet long pipe. The factors in the table are for pipes of smooth interior, as wrought iron, brass, or lead.
Examples. A 11/2 inch pipe, 100 feet long, connected with a tank, is to discharge 35 gallons per minute. At what elevation above the end of the pipe must the surface of the water in the tank be to produce this How?
How many gallons will be discharged through a 2 inch pipe, 100 feet long, when the inlet is 22 feet above the outlet? In table No 1 we find a head of 22 feet corresponds to a pressure ot 9 53 pounds Then, looking in table No 2, we find in the column of Friction Loss for a 2 inch pipe that a pressure of 9 46 corresponds to a discharge of 100 gallons per minute.
