Max RPM for Centrifugal Pump

[tmartin125]

Is there a maximum RPM for a centrifugal pump? I was just quoted a centrifugal sea water pump operating at 6756 RPM. Wont it wear out quickly at this speed? Pump material is 2205 duplex stainless.

 

[racookpe1978]

Did they design the pump and impeller material and seals and thrust bearing for that speed in that fluid?

High rotation usually means problems with impller and casing erosion yes, but also with NPSH and cavitation. You can meet a high speed with the right motor, but just because it "can" run that fast doesn't mean that it "should be" running that fast. Do you really want to turn it that fast? Usually is cheaper to go slower.

 

[tmartin125]

I'm somewhat limited on options with the required duty point. We need to move sea water at 240 GPM @ 380 PSI. The subject pump is one of the only ones vendors have quoted. The balance quoted are 50K more expensive. I did confirm the subject pump has a gear box so the drive motor only runs at 3600 RPM. NPSHr is 14ft which works with our system. I have to assume pump material was designed for the duty point but I do not know for sure.

 

[racookpe1978]

At the prices called out on today's quote, go back to that vender and demand his warranty period and conditions (what length he will guarantee performance for) under the service environment the pump (seals, motor, pressure, temperature, fluid, oil & lube requirements for the gearbox, etc) will see. Don't make assumptions.

 

[tmartin125]

Good advice. I will definitely do that. Appreciate your help!

 

[BigInch]

Speed is hard on the pump as well as the motor.
Just because the vendor wants to sell you this, doesn't mean it's a good idea.
It's attractive because high speed means smaller and cheaper.
One way or another you will pay now or later.
No free lunch as they say.
To level the playing field, make sure the warranty is for parts, labor and ... lost production.

I hate Windowz 8!!!!

 

[DubMac]

Wear increases to the 3rd power of speed increase. Double the speed, 8 times the wear! You are pumping seawater? Depending on how far from shore and how deep you are drawing from, sand content could wear that pump out in no time; nothing worse than sand for wear.

Can't believe your duplex stainless pump with a gearbox is much cheaper than a traditional 3600rpm centrifugal; or will have less reliability/Maintenance issues. You could look at a two stage offering from most any of the big players.

 

[Artisi]

Would be interested in some additional detail of the pump offered at 6756RPM (just love the "6" - certainly seems a very precise selection )
How about posting make, model, curve etc. for us all to see.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[tmartin125]

Quote is attached.

 

[Artisi]

Clear now that the pump has been identified.
Don't see any problem with the selection - one can only assume the vendor knows that he is specifying / supplying.

Wear out in what way? erosion of the wetted parts, bearings / seals, gearbox ??

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[BigInch]

"Don't see any problem with the selection - one can only assume the vendor knows that he is specifying / supplying."
As long as "cavet emptor" is equally in force.

I hate Windowz 8!!!!

 

[DubMac]

Sundyne does make a good pump; had no idea they offered one for seawater though. It is designed to run at the high speed, so I wouldn't be worried about the mechanical portion of the pump as much as any parts that contact possible solids in the seawater. Do you have any data on expected solids? If you put filters ahead of the pump, make sure your NPSH margin is not jeopardized. You do have a Plan 11, so you are flushing your seals with pumpage; might want to look at fresh water flush if available.

The only other options I can think of that could perform the Conditions of Service would be:

- typical 2-stage centrifugal splitcase run at 3600rpm. Many make them; seawater materials (NiAlBrz, CD4MCu, Duplex, etc) could make this cost prohibitive.
- vertical turbine style pump laid horizontally. This might take too many stages and could be very expensive if you had more than 410 series stainless fitted. However, you could possibly get away with 1800 rpm selection with a large diameter impeller; think lifetime costs.

WOuld like to see a $$ comparison of up front costs between these styles.

 

[StoneCold]

This application sounds like a Sundyne application. If it is one of theirs you should have pretty good luck. They are known for high head low flow applications.

Regards
StoneCold