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I I I I I I I I I I I I I I I I I I I minimum and maximum tank levels. If three tanks are used, the controllers should be identical, allowing a spare to be provided that can function for any one not workin(j. These controls will be such that a manual override can be induced. The manual operation will he simole; open a valve to any tank to fill, and shut off wh~n filled to the desired level. The valves will not be designed for low flow throttling, and as mentioned ea~lier, they will be desi'lned to control rate of closure even when manually oDe~ated. 3.4.2 Metering The total volUMe of water supplied to Towaoc must be measured. It is also desirable to have rate-of-flow indication. With the water supply line generally operated fully open or fully c10serl, the flows to be measured ~/ill generally be in the 800 to 1350 gpm range, except when the control val ves are in the process of opening or closing. In the event that Towaoc someday treats its own water, it is reco~ended that the selected meter be suitable for both treated water and raw water applications. ~ecause of the relatively low hydrau1 i c gradi ent avai 1 abl e to provi de flow to Towaoc, the flow meter type and size will be selected to keep the head loss small, even at the peak design flow rate. Based on these criteria, either a magnetic, an ultrasonic, or differenti'll pressure meter is proposed. To minimize hea1 losses, the meter s~ould probably be no smaller than eight inches. The meter wil 1 be housed in a vault near the tank and provi ded wi th a lonq- term recorder. There will be additional valvin'l in this valllt that will allow manual shut off of the entire line to provide the capability to isolate the line in case of a break, or to make repairs. 3.4.3 Va1ving and Drainage The Towaoc water supply line \~ill need other valves besides the automatic control valves discussed above. Air release and vacuum valves will be 3~l Ii l060c