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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />3.4 Controls, Metering, Valving, and Drainage <br /> <br />3.4.1 Controls <br /> <br />Control valves are needed at the downstream end of the water supply pipeline <br />to regulate the pipeline flow. Two principal alternative operation techniques <br />have been considered. They are: 1) Using automatically modulating valves to <br />regulate the flow so as to maintain a given reservoir level, and 2) Using <br />automatically controlled valves \~hich fully open when the reservoirs reach <br />predetermined levels and require filling and then fully close when the <br />reservoirs have refilled. <br /> <br />The modulating scheme or flow rate controlling requires significantly more <br />complex and costly controls in order to solve the potential cavitation <br />probl ems that wi 11 ari se when flows are si gnifi cant1y 1 ess than the desi gn <br />flow rate. Operating valves in the fUlly open or closed positions essentially <br />eliminate the cavitation problems at the control valves. Primarily for this <br />reason, it is recommended that this latter flow control scheme be implemented. <br /> <br />The recol1Jllended control scheme wi 11 have the effect of drawi ng water from the <br />Cortez storage tank at peak design rates. However, the watel" will be taken <br />from a 2,000,OOO-gal10n reservoir, and if taken in batches that are small <br />compared to thi s reservoi r si ze, Cortez shou1 d noti ce no adverse effects. In <br />the event that Towaoc someday taps into the raw water supply line, taking <br />water at the design flow rate should not present a significant problem since <br />the feeder line above the Cortez plant was built with the capacity to supply <br />To\~aoc wi th up to 1320 gpm. In order to 1 imi t hydraul i c transi ents in the <br />Towaoc pipeline, the control valves must be automated so that they close and <br />open very slowly (in the order of several minutes). The rate of closure must <br />be evaluated in conjunction with the valve type and size, and the pipeline <br />type and class. <br /> <br />There wi 11 be a set of control s for each of the storage tanks. The control s <br />will monitor the water level in the tank and activate the valves to the on and <br />off positions. The controllers will allow changes in the settings for the <br /> <br />3-15 <br /> <br />l060c <br />