Pump Suction Piping Rules – Cooling Tower Pumps and Piping – Part 8
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Traditional hydronic piping system designers use tools such as the Xylem Bell & Gossett System Syzer for pipe sizing. You may find this program at http://completewatersystems.com/brand/bell-gossett/selection-sizing-tools/system-syzer/. Tower manufacturers, the Hydraulic Institute (HI), and Bell and Gossett all suggest lower velocity for pipe selection in cooling tower pump suction piping. Bell and Gossett has several pipe sizing suggestions in their manual TEH-1209.
Many an engineer will point to many a project with the comment “I’ve never had an issue while following these suggestions”. The engineer is probably correct. It’s likely, if you do enough cooling tower projects, eventually, one will go bad. These suggestions are made to help avoid the problem job, which sometimes shows up.
EXAMPLE: Three towers at 2000 GPM each for a total of 6000 GPM in the pump suction header and three pumps at 2000 GPM at 60 feet each. Tower pan is 5 feet above grade.
SOLUTION: The pump is a B&G VSCS-6X8X10.5A at 40 HP with 10 foot NPSH. 2000 GPM leaving the tower should be 14” at 4.74 FPS. (Rule 4). 6000 GPM in the common pipe should be 30” at 2.97 FPS velocity. (Rule 3) We would select 24” at 4.79 FPS if the 30” pipe caused elevation issues with the pump on a housekeeping pad. Pump suctions would remain at 14” and we’ll use 2 reducers to the 8” suction. (Rule 1, 2, 6).
Disclaimer: R. L. Deppmann and it’s affiliates can not be held liable for issues caused by use of the information on this page. While the information comes from many years of experience and can be a valuable tool, it may not take into account special circumstances in your system and we therefore can not take responsibility for actions that result from this information. Please feel free to contact us if you do have any questions.