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#1

# What's the maximum tip speed for a centrifugal pump's impeller?

What's the maximum tip speed for a centrifugal pump's impeller?
02-24-2014 12:38 AM
Top #2
I will try to give a personal opinion as user, not designer.
Impeller Diameter and Speed are based in flow and the head developed from chosen specific speed. This is the first step involving basic hydraulics.
Then we have to take an account velocity limits for cast materials according fluid pumped.
To finalize design of the impeller to withstand mass forces due to centripetal acceleration, here mechanical materials properties and shape of impeller are the key factor.
Speed limits so depend on a number of variables : head, specific speed, fluid pumped/ speed limit for material and strength/ shape. But if still you like to have a rough estimated value think in 150 m/s in "low" specific speed pumps with clean and "friendly" liquids for material chosen
02-24-2014 03:09 AM
Top #3
I'd agree with Isidro, that 150 m/s in ideal conditions with a high strength material like CA6NM (Martensitic stainless steel) is generally the upper limit.

However getting close to that limit requires that the hydraulic and mechanical design are of high quality. At these sort of speeds:

- The fatigue of the impeller shrouds needs to be considered (I've seen incorrectly designed pumps fail in 48 hours of running)

- The B3 to B2 (impeller vane to diffuser/volute) clearance needs to be large in order to avoid excessive pressure pulsations and pump vibration

- Any significant solids in the pumped fluid, can cause rapid erosion of the impeller or casing.

These are general observations. If you have a specific application in mind, please post what it is and I can be more specific as to the velocity limits that Goulds would recommend.
02-24-2014 05:57 AM
Top #4
How can one calculate tip Speed for different Materials in Ideal conditions. Can some one suggest for write-up/ Technical paper or technical Book?
02-24-2014 08:43 AM
Top #5
Every pump company has its own methodologies that tend to be not in the public domain due to the high cost of the R&D in determining what works (and what does not).

Of the information in the public domain, the book Centrifugal Pumps by Johann Gülich has some good advice on maximum tip speeds for different materials
02-24-2014 10:47 AM
Top #6
Sorry one error in my previous comment. It should state D3 to D2 and not B3 to B2
02-24-2014 12:56 PM
Top #7
I have read in KSB Pumps literature that maximum Impeller speed is 40 m/s
02-24-2014 02:59 PM
Top #8
Impeller Tip Speed (ft/s)= (3.14/720) x RPM x Dia of Impeller(Inches)
Tip speed depends on impeller material & service fluid.
As a general For
Clean water----------145 ft/s
Dirty water-----------130 ft/s
Medium slurries-------115 ft/s ( less than 25% solid content in slurry)
High slurries-----------100 ft/s ( more than 25% solid content in slurry)
Elastomer impeller-----85 ft/s
02-24-2014 05:37 PM
Top #9
Dear Murli
I think tip speed also depends on material of construction
02-24-2014 08:28 PM
Top #10
Dear Murli
I think tip speed also depends on material of construction
02-24-2014 10:32 PM
Top #11
All infos above are accurate. I'll add to use the basic velocity formula: V=WR
Elastomer (rubber, hypalon, etc) impellers in slurry application is calculated lower than metal impeller in water application.
Pump manufacturers keep this info as proprietary. They will tell us that are the limitations, which is sufficient for users.
I've seen heavy erosion on Hypalon impeller in light slurry and Hcl application and solved it in bigger pump and lower speed.