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Grade (slope) needed for flow between settlement tanks (in series)

Grade (slope) needed for flow between settlement tanks (in series)

Grade (slope) needed for flow between settlement tanks (in series)

(OP)
Hi.

We are putting together a simple water treatment plant, consisting chemical feed to the water stream thence settlement inside round tanks.

There are five settlement tanks (approx 12,ooo gal each, 9'6" high) piped together in series, all open to atmosphere.  Water will be pumped (discharged) into the first tank at a maximum flow of 555 gal/minute, thence flow through the five tanks under gravity.  Each tank will decant from the top, then flow to the next tank through 3 x 8" pipes (ID of 7.5").  The distance from the top of the decant pipes to the overflow (very top) of the tank is 3".  The tanks are 4' apart and the 3 x 8" decant pipes are 5' in length (inward projection inside the tanks).  The water will then exit the last settlement tank in the series and discharge into a smaller (and lower) discharge tank.  The pipes into the discharge tank will have an elbow downturn and will empty into the bottom of the discharge tank.  Water level in the discharge tank will vary because it is a feed tank to another downstream treatment process, but the difference in water levels between the last settlement tank and the discharge tank will never be less than 18".  We will keep all the 3 x 8" decant pipes full by installing an (adjustable) weir between the last settlement tank and the discharge tank.  We wish to keep the flow velocity between  all the tanks as slow as possible.  The total length of the tank-series footprint is 115'

What would be the minimum grade (slope) required on the tank footprint to ensure system integrity (no overflows anywhere)?

RE: Grade (slope) needed for flow between settlement tanks (in series)

Set your pipes to the flow you need to pump out of 'whatever'.  

Richard A. Cornelius, P.E.
WWW.amlinereast.com

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