Pump Suction Piping Rules – Cooling Tower Pumps and Piping – Part 6

Norm Hall
May 14, 2012
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Over the last several weeks we discussed the feared NPSH and showed it is rarely an issue at design conditions. More often than not, noise and pressure problems are caused by air in the suction piping system. The suction pipe, in many cooling pumping systems, is under very little pressure. In fact, the suction of the pump could be under a vacuum.


Bell and Gossett has several piping rule suggestions for cooling tower pump suctions.

RECOMMENDATION #1: Always specify an anti-vortex baffle, sometimes called a doghouse, in the tower outlets.

Towers normally have very low storage heights of water in the basin. Any vortex that starts will reduce the flow rate and pull air into the piping system.

Vortex and tower water level diagram

RECOMMENDATION #2: Avoid air traps caused by elevation changes in the suction pipe. Elbows used to go up & over pipe or obstacles cause an air trap. The improper use of a reducer at the pump flange can have the same effect.

Air traps in suction pipe. Not recommended.

RECOMMENDATION #3: When needed, use eccentric reducers at the pump suction. The orientation depends on where the suction pipe is located.

In both examples, we avoid trapping air while transitioning pipe sizes.

eccentric reducer and long radius elbow. Recommended.

Next week we will continue to look at cooling tower pump suctions.

Click here to request a copy of the Xylem Bell and Gossett
Cooling Tower Piping technical bulletin TEH-1209

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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.