Pump Suction Straight Run

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16 years 4 months ago - 16 years 4 months ago #4365 by Anton
Replied by Anton on topic Reducer straight on to the
Reducer straight on to the suction nozzle is fine ... the straight section (5D / 10D whatever your standard) would be to the first elbow, tee, valve etc..

- If you're the smartest person in the room ... you're in the wrong room.

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16 years 4 months ago - 16 years 4 months ago #4366 by 2ndMoment
Replied by 2ndMoment on topic Apart from the valuable data
Apart from the valuable data available from the Hydraulic Institute, another credible source for back up as a hard reference may be found in the book:

Troubleshooting Centrifugal Pumps and their Systems by Ron Palgrave.

It is explicitly stated that 5 diameters of straight run pipe after an elbow or tank nozzle before the pump suction (or sensitive process equipment) is recommended. As the book is an EXCELLENT source of empirical knowledge I would use it as a rule.

For reducers directly onto the pump suctions, As Jop stated this is standard practice in order to increase the NPSHa to the pump suction. However, for suction lines running without a lot of “meat" between the NPSHr and NPSHa, although the impeller may be healthy, I have seen cavitation damage on the reducer due to turbulence - an unfortunate downside.

Thanks
2ndMoment

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16 years 4 months ago - 16 years 4 months ago #4367 by Bob
Replied by Bob on topic thanks!
I hadn't heard of API 686 before gpsvn's post and thanks 2nd Moment for the tip on Ron Palgrave's book. gpsvn... would you happen to know where I can get a copy of API 686, or at least the excerpt on the 5 diameters? I don't want to infringe on copyrighted material, but would like to learn more (smiling)...

This all goes to show that if a needy piping designer (like poor old Bob) needs pertinent, accurate and timely information... just visit one of the PipingDesigners.Com forums... thanks guys! Thanks also to James and Anton... the guys that keep this valuable flow of information from cavitating (smiling)...

Bob

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16 years 4 months ago - 16 years 4 months ago #4368 by gpsvn
Replied by gpsvn on topic I do have a copy
I do have a copy in pdf. I Google for the first sentence and found it at www.lightmypump.com/forum/showthread.php?t=1307 so I think it's ok to copy the same excerpt and share it here. In addition, I copy the note explaining the rational behind the requirement for clarity.

3.1.2.6 The pump suction line shall have a straight run (typically five pipe diameters) between the suction flange and first elbow, tee, valve, reducer, permanent strainer, or other obstruction sufficient to ensure stable and uniform flow at the pump suction nozzle.

Note: A piping straight run length of five pipe diameters, based on the pump suction nozzle size, is usually sufficient to ensure stable and uniform flow at the pump suction nozzle. In some situations, the type and orientation of valves and elbows in the pump suction line may affect the flow distribution to the impeller and necessitate a longer piping straight run length. Flow straighteners may also be utilized to reduce the piping straight run length.

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16 years 4 months ago - 16 years 4 months ago #4370 by thehat
Replied by thehat on topic It is irelevant what codes
It is irelevant what codes and standards say.

If the pump vendor wants 15d or 10d or what ever then that whats required.

Anything less may void the warranty.

So look in the I/O manual for installation requirements.

I would be more worried about axial thrust on the bearings than cavitation. As would a vendor.

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16 years 4 months ago - 16 years 4 months ago #4382 by pipingguy
Replied by pipingguy on topic Light My Pump (ex-FluideDesign.com)
I see you've read my buddy Jacques' writing. There's a lot more interesting pump and hydraulic-related stuff at his site, including home-grown, kitchen video experiments that demonstrate pressure and other neat stuff.

Jacques is a pretty cool guy, a karate black belt instructor but also an engineer. Two out of three ain't bad.

Uh-oh, I hope he doesn't kick my ass next time I see him.

Paul
pipingdesign.com

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