Frictional Heads at Given Rates of Discharge in Clean Cast-iron Pipes for Each 1000 Feet of Length. (Condensed from Ellis and Howland's Hydraulic Tables.) Effect of Bends and Curves in Pipes.-Weisbach's rule for bends: Loss of head in feet = = internal radius of pipe in feet, R = radius of curvature of axis of pipe, v = velocity in feet per second, and a = the central angle, or angle subtended by the bend. Hamilton Smith, Jr., in his work on Hydraulics, says: The experimental data at hand are entirely insufficient to permit a satisfactory analysis of this quite complicated subject; in fact, about the only experiments of value are those made by Bossut and Dubuat with sinall pipes. Curves. If the pipe has easy curves, say with radius not less than 5 diameters of the pipe, the flow will not be materially diminished, provided the tops of all curves are kept below the hydraulic grade-line and provision be made for escape of air from the tops of all curves. (Trautwine.) Hydraulic Grade-line.-In a straight tube of uniform diameter throughout, running full and discharging freely into the air, the hydraulic grade-line is a straight line drawn from the discharge end to a point immediately over the entry end of the pipe and at a depth below the surface equal to the entry and velocity heads. (Trautwine.) In a pipe leading from a reservoir, no part of its length should be above the hydraulic grade-line. Flow of Water in House-service Pipes. Mr. E. Kuichling, C.E., furnished the following table to the Thomson Meter Co.: Discharge, or Quantity capable of being delivered, in under the conditions specified in the first column. Nominal Diameters of Iron or Lead Service-pipe in In this table it is assumed that the pipe is straight and smooth inside; that the friction of the main and meter are disregarded; that the inlet from the main is of ordinary character, sharp, not flaring or rounded, and that the outlet is the full diameter of pipe. The deliveries given will be increased if, first, the pipe between the meter and the main is of larger diameter than the outlet; second, if the main is tapped, say for 1-inch pipe, but is enlarged from the tap to 14 or 11⁄2 inch; or, third, if pipe on the outlet is larger than that on the inlet side of the meter. The exact details of the conditions given are rarely met in practice; consequently the quantities of the table may be expected to be decreased, because the pipe is liable to be throttled at the joints, additional bends may interpose, or stop-cocks may be used, or the back-pressure may be increased. Air-bound Pipes.-A pipe is said to be air-bound when, in consequence of air being entrapped at the hign points of vertical curves in the line, water will not flow out of the pipe, although the supply is higher than the outlet. The remedy is to provide cocks or valves at the high points, through which the air may be discharged. The valve may be made automatic by means of a float. = height of jet, Vertical Jets. (Molesworth.)-H= head of water, h d = diameter of jet, K = coefficient, varying with ratio of diameter of jet to head; then h = KH. If H = d X 300 600 1000 1500 1800 2800 3500 4500, .96 .25 Water Delivered through Meters. (Thomson Meter Co.).—The best modern practice limits the velocity in water-pipes to 10 lineal feet per second. Assume this as a basis of delivery, and we find, for the several sizes of pipes usually metered, the following approximate results: Nominal diameter of pipe in inches: 3% 5% 34 1 12 2 3 4 6 Quantity delivered, in cubic feet per minute, due to said velocity: Average minimum price for 1000 gallons in 163 places... 66 maximum 66 66 FIRE-STREAMS. Discharge from Nozzles at Different Pressures. (J. T. Fanning, Am. Water-works Ass'n, 1892, Eng'g News, July 14, 1892.) Friction Losses in Hose.-In the above table the volumes of water discharged per jet were for stated pressures at the play-pipe. In providing for this pressure due allowance is to be made for friction losses in each hose, according to the streams of greatest discharge which are to be used. The loss of pressure or its equivalent loss of head (h) in the hose may be found by the formula h = v2 (4m) 2gd In this formula, as ordinarily used, for friction per 100 ft. of 2-in. hose there are the following constants: 21⁄2 in. diameter of hose d=20833 fɩ.; length of hose 1 = 100 ft., and 2g= 64.4. The variables are: v = velocity in feet per second; h = loss of head in feet per 100 ft. of hose; m = a coefficient found by experiment; the velocity v is found from the given dis charges of the jets through the given diameter of hose. Head and Pressure Losses by Friction in 100-ft. Lengths of Rubber-lined Smooth 21⁄2-in. Hose. These frictions are for given volumes of flow in the hose and the velocities respectively due to those volumes, and are independent of size of nozzle. The changes in nozzle do not affect the friction in the hose if there is no change in velocity of flow, but a larger nozzle with equal pressure at the nozzle augments the discharge and velocity of flow, and thus materially increases the friction loss in the hose. Loss of Pressure (p) and Head (h) in Rubber-lined Smooth 2%-in. Hose may be found approximately by the formulæ 1q2 lq2 p = and h = in which p = pressure lost by friction, in 4150d5 1801d5 pounds per square inch; 1= length of hose in feet; q = gallons of water discharged per minute: d = diam. of the hose in inches, 21⁄2 in.; h = frictionhead in feet. The coefficient of d would be decreased for rougher hose. The loss of pressure and head for a 1%-in, stream with power to reach a height of 80 ft. is, in each 100 ft. of 2-in. hose, approximately 20 lbs., or 45 ft, net, or, say, including friction in the hydrant, 2 ft. loss of head for each foot of hose. If we change the nozzles to 14 or 13% in diameter, then for the same 80 ft. height of stream we increase the friction losses on the hose to approximately ft. and 1 ft. head, respectively, for each foot-length of hose. These computations show the great difficulty of maintaining a high stream through large nozzles unless the hose is very short, especially for a gravity or direct-pressure system. This single 1%-in, stream requires approximately 56 lbs pressure, equiva lent to 129 ft. head, at the play-pipe, and 45 to 50 ft. head for each 100 ft. length of smooth 2-in. hose, so that for 100, 200, and 300 ft. of hose we must have available heads at the hydrant or fire-engine of 179, 229, and 279 ft., respectively. If we substitute 14-in. nozzles for same height of stream we must have available heads at the hydrants or engine of 133, 259, and 325 ft., respectively, or we must increase the diameter of a portion at least of the long hose and save friction-loss of head. Rated Capacities of Steam Fire-engines, which is perhaps one third greater than their ordinary rate of work at fires, are substantially as follows: 3d size, 550 gals. per min., or 792,000 gals. per 24 hours. 2d 700 66 1st " 1,008,000 46 66 Pressures required at Nozzle and at Pump,with Quantity and Pressure of Water Necessary to throw Water Various Distances through Different-sized Nozzlesusing 21⁄2-inch Rubber Hose and Smooth Nozzles. (From Experiments of Ellis & Leshure, Fanning's "Water Supply.") pressure at For For greater length of 2-inch hose the increased friction can be ob tained by noting the differences between the above given nozzle" and " pressure at pump or hydrant with 100 feet of hose." instance, if it requires at hydrant or pump eight pounds more pressure than it does at nozzle to overcome the friction when pumping through 100 feet of 21⁄2-inch hose (using 1-inch nozzle, with 40-pound pressure at said nozzle) then it requires 16-pounds pressure to overcome the friction in forcing through 200 feet of same size hose. Decrease of Flow due to Increase of Length of Hose. (J. R. Freeman's Experiments, Trans. A. S. C. E. 1889.)-If the static pres sure is 80 lbs. and the hydrant-pipes of such size that the pressure at the hy drant is 70 lbs., the hose 2%1⁄2 in. nominal diam., and the nozzle 1% in. diam., the height of effective fire-stream obtainable and the quantity in gallons per minute will be: With 500 ft. of smoothest and best rubber-lined hose, if diameter be exactly 21⁄2 in., effective height of stream will be 39 ft. (177 gals.); if diameter be in. larger, effective height of stream will be 46 ft. (192 gals.) THE SIPHON. The Siphon is a bent tube of unequal branches,"open at both ends, and is used to convey a liquid from a higher to a lower level, over an intermediate point higher than either. Its parallel branches being in a vertical plane and plunged into two bodies of liquid whose upper surfaces are at different levels, the fluid will stand at the same level both within and without each branch of the tube when a vent or small opening is made at the bend. If the air be withdrawn from the siphon through this vent, the water will rise in the branches by the atmospheric pressure without, and when the two columns unite and the vent is closed, the liquid will flow from the upper reservoir as long as the end of the shorter branch of the siphon is below the surface of the liquid in the reservoir. If the water was free from air the height of the bend above the supply level might be as great as 33 feet. |