Operation

balance the makeup water with tower operation. Ideally, the float valve setting will be such that no water is wasted through the overflow at pump shutdown. However, the water level after pump start-up must be deep enough to assure positive pump suction.

5.If a multicell tower installation is equipped with flow-control valves, adjust them to equalize hot water depth in the distribution basins after reaching design water flow rate. Each basin should have from 23⁄4" to 51⁄2" (70 mm to 140 mm) water depth, with uniform depth from basin to basin. Fix valves in this position when depth is correct. If the tower is a single cell installation this step is not necessary.

Uniform distribution depth of 23⁄4" to 51⁄2"(70 mm to 140 mm) is essential to efficient tower operation. Contact your Marley sales representative if you are considering a permanent change in circulating water flow rate that would prevent operation within these limits.

6.Continue pump operation for about 15 minutes, after which it is rec- ommended that the water system be drained, flushed, and refilled.

7.While operating the condensing water pump(s) and prior to operat- ing the cooling tower fan, execute one of the two alternative biocidal treatment programs described in the following:

•Resume treatment with the biocide which had been used prior to shutdown. Utilize the services of the water treatment supplier. Maintain the maximum recommended biocide residual (for the specific biocide) for a sufficient period of time (residual and time will vary with the biocide) to bring the system under good biological control

•Treat the system with sodium hypochlorite to a level of 4 to 5 mg/L

(ppm) free chlorine residual at a pH of 7.0 to 7.6. The chlorine re- sidual must be held at 4 to 5 mg/L (ppm) for six hours, measurable with standard commercial water test kits.

If the cooling tower has been in operation and then shut down for a duration of time and not drained, perform one of the two previous biocidal treatment programs directly to the cooling water storage vessel (cooling tower sump, drain down tank, etc.) without circulating stagnant water over the cooling tower fill or operating the cooling tower fan. After biocidal pretreatment has been successfully completed, cooling water may be circulated over the tower fill with the fan off.

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