Arizona republican., 1919-06-12

or lSt0u0 gallons per minute. This, for convenience of calculation, may be stated as follows:
 Normal service 10,500 gallons per equal to 9 cubic feet per sec ond.
 Emergency service, 1s,0oO gallons per minute, equal to 40 cubic feet per second"
 Service Reservoir
 You are proposing to establish a service reservoir at 8 point which will maintain a minimum pressure of 60 pounds per square inch at the center of distribution in your city. Your pro- posed reservoir is to have capacity of 25,O0O,00o gallons.
 An inspection of the contour map and of the ground itself indicates a very favorable location, substantially on the 1250-foot contour, and approxi- mately one half mile south of the Ari- zona Falls power house.
 At first sight, it might appear that the inflow line between the intake and the service reservoir would be called upon to supply only the normal and average demand of 15,000, 900 gallons per day, or 23 cubic feet per second. If so, a S6-inch pipe would be ample. I will show later, however that this as- sumption is not safe.
 'The outflow line from the service reservoir to the center of distribution in the city must necessarily be propor- uoned within itself to carry the emerg- ency demand of 40 cubic feet per sec ond. review these two lines separately.
 Inflow Line
 "The total length from the service reservoir to the intake over the new line as at present located is 13O.700 feet, The difference of ground eleva- ton between the two points is 135 feet. This may, therefore, be taken as the available head when the reser- voir is empty. On the other hand. when the reservoir is full, this head will be diminished by 20 feet, leaving a net head of 115 feet.
 Tn the report of your city engineer. a 42-lnch pipe is recommended. This pipe will work under two conditions of service, normal flow and emergencr lIoW-and two other related conditions. namely, the service reservoir full and empty corresponding to the respective headS or ll5 feet and 135 feet.
 In computing the flow it is sllffi- clently accurate to assume the pine to be straight. There are. in fact numer- ous small Reflections aggregating a total curvature of 4S0 degrees. There IS also siphon under the canal. If these deflections are handled bv ,sne- clals' with a proper radius of curvature. their effect on the total flow will be practically negligible.
 Ihere will also be some resistance que to the sudden expansion of the pipe on entering the reservoir. This can De mlnimized by a special form of construction which can be examined when details are un6er consideration
 with the reservoir full, the inflow pipe will deliver in round numbers 35 cuDlc rect per second, equal to K 75o gallons per minute There will there0 lore be an excess of flow into the res erVolr over the average normal draft amounting to between 5000 and 00o gallons per minute, which must he amply provided for by an adeouafe waste-way. Of course, there are times ouring the night when the overflow VIII be materially exceeded and inc waste way must be proportioned ac- cordinsly. Fortunately there is an excellent opportunity at the proposed reservoir site for discharging the over IioW lnto one of the canals and SD NSiAANAiS US lTFlBdIlOn Nalnp
 under emergency draft, the inflow plpe VIII Tall short of the full supply to the extent of 3l gallons per second I ne water level in the reservoir will therefore slowly subside AS if faue .he elIecuVe head on the inflow line increases with corresponding increase ot discharge. If the emergency f1oy1 is continued until the reservoir is amnt,, the inflow under the head Of 1a5 feat VIII still be seven gallons Der second snort of the emergency requirements, The average deficiency will he 9IIL gallons per second. from which if "a n oe computed that the reservoir will last Tor 5l hours at a maximum enerp- ehcy HOW Of lS,000 gallons per minute
 IL seems to me that here is annie margin of safety for even the nost eAtehslVe conflagration. In such . crlsls all excessive use of water ae TOT lawn sprinkling, etc. wouId nat- trally cease, and the city autboritiae would undoubtedly issue warning to fbe cltZens to minimize the draft of water at all points. l think. therefore that no practical conditions can arise in winch the safety of the City can he JeopardlZed because of an inadeouat te supply in emergency. Ut must he rel memhered that all these computations are based on population of 75 O00 people). 'V''''
 Outflow Line
 nave taken the center of distrib,-
 ton as being at the corner of Seventh ana FOX streets. The total Curvature between that point and the service res. erVolr amounts to 120 degrees. of which sV degrees IS in one angle about one hlle north of the center of distribn- Iioh. rms angle should be carried on ticable. 10 prac 10 A similar computation, assuming q 4z-lnch pipe, and having referepca +o the emergency draft of 49 cuhic foe. per second, SHOWS a total loss of head Including curvature. of IA feet tha +ota- distance being 3S.300 feet and inc GiS ference of elevation 1eo feet Tb, aooYe Is with the reservoir snhstan' tialiy empty. With the reservoir fulI the effective head will be 1SO feet. Wlth the reservoir substantialI, empty there will then be an effectiy, mead al the center of distribution n, LIZ leet' corresponding to 4S.6 pounds Ihls IS sufficiently close to the 5t pounas required to justify the use oi .ne 9S7ineh pipe. It will be remen, i. pered, moreover, that this effective mead IS increased to an amount moi readily eomputable, by the suction Q, | the fire apparatus. VI
 The further reduction of pressurs due to distribution through the citS mains to any given point of fire sery. Ice IS outside the province of this re. port.
 I again point out the fact that the inflow at the service reservoir is prac. tically unrestricted except by the vary. ing head; whereas the flow in the lower section of the pipe is controlled by the hydrants and other service gates and cocks. It is not likely, therefore that under any working conditions con. ceivable to arise, the service reseryoi, can be drawn down to a point which will uncover the intake of the outflow