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16 comments
Member

Join Date: Jun 2008
Location: Malaysia
Posts: 9

Can a centrifugal pump be considered a low-shear pump?

07/16/2008 9:48 PM

Dear members,

Generally centrifugal pumps are considered high-shear pumps and usually the running speed is either 3000 or 1500 rpm (2 or 4 pole motor, 50Hz system). If these pumps are to be operated at lower speed say 600 or 500 rpm (10 or 12 pole motor), will they become low-shear pumps? Particularly I am refering to single stage end suction centrifugal pumps. I consider shear rate of 100 inverse seconds or lower is low-shear. (I am not sure whether centrifugal pumps can be operated at 600 or 500 rpm.)

Comments or feedback is appreciarted.

Thank you.

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Guru
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#1

Re: Can a centrifugal pump be considered a low-shear pump?

07/17/2008 7:45 AM

Not really.

The term "llow shear pumps" encompasses peristaltic and lobe pumps, among others.

Consider what pumps can be used to convey strawberry jam, or blood, without disrupting the solids in the fluid.

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#4
In reply to #1

Re: Can a centrifugal pump be considered a low-shear pump?

07/18/2008 8:01 AM

good answer PWslack,

one thing, I like to add, is determined or define shear, which depends on the product's Rheology. (relatively speaking)

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#2

Re: Can a centrifugal pump be considered a low-shear pump?

07/18/2008 7:11 AM

Centrifugal pumps can, indeed, be operated at speeds as low as 500 RPM. The question you pose is interesting, but there isn't sufficient informaton to determine if the centrifugal pump is applicable to your particular situation. I have used centrifugal pumps to pump whole tomatoes without damage, and I have used them to pump live fish without damage. I believe that qualified them to be considered low shear.

The first consideration is the medium you are pumping. If it is large solids, such as fish or tomatoes, you will want to consider a pump designed for that service. These are normally described with such names as non-clog pumps, solids handling pumps or trash pumps. They usually have an open or semi-open impeller that can pass solids as high as 4 to 5 inches in diameter.

The second consideration is where you want this pump to discharge. How much elevation difference and how long is the discharge pipe? The lower speed pumps are generally not able to develop a lot of head (pressure). That is because head is a function of the "tip speed" of the pump impeller. The only way to increase the head is to increase the tip speed. Lower speed pumps normally have an impeller that is rather large in diameter to allow them to develop a higher tip speed while maintaining a relatively slow rotative speed.

Interesting question you have posed here. I hope this helps you a little. Generally, if you are pumping a lot of liquid, the centrifugal will probably be your best option if the head requirements aren't that great. Good luck!!

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#5
In reply to #2

Re: Can a centrifugal pump be considered a low-shear pump?

07/21/2008 1:57 AM

crownvic, thanks for the commetns.

The medium being pumped is Produced Water (SG=0.99, Visc=0.39 cP) from offshore oil production. It contains hydrocarbon crude oil & seawater. The service is Hydrocyclone Pump. The pump shall be low speed low shear type to minimize oil troplet attrition.

The pump is required to boost up low pressure of produced water from MP Separtator to the MP Hydrocyclone vessel. The discharge head is 78 m, suction head is 32 m and the differential pressure is 46 m. The required flow rate is 104 M^3/hr. The available NPSH is only 0.97 m.

Do you know any centrifugal pump can handle this application and what would be the shear rate?

Regards.

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#8
In reply to #5

Re: Can a centrifugal pump be considered a low-shear pump?

11/10/2009 4:35 AM

We may have a pump that will meet your duty requirements please send datasheet to enquiries@amarinth.com.

Steve

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#13
In reply to #5

Re: Can a centrifugal pump be considered a low-shear pump?

03/30/2010 9:26 AM

Dear Elvis Chong

Just seen your comments on teh forum, Low shear centrifugal pumps have you considered vortex pumps? try web site www.eggerpumps.com we have many installations where low shear of either solids or liquid is required. We also have these pumps in refineries pumping oily water to separators and they have proven to be very successful over many years.

If we can help please contact us

Regards

Ron Franklin

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#14
In reply to #13

Re: Can a centrifugal pump be considered a low-shear pump?

03/31/2010 12:10 AM

Thanks for the info. Should I have requirement for such pumps. I will contact you.

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Associate

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#3

Re: Can a centrifugal pump be considered a low-shear pump?

07/18/2008 7:13 AM

I'm not aware of a formal definition of "Low shear", but you provided your own criteria (thank you!). For any given centrifugal pump, shear will be reduced as speed is reduced, but I agree with the other feedback provided. Peristaltic, diaphragm, progressing cavity, and lobed pumps are normal choices for low shear. There are some other special purpose pumps of similar designs to those just mentioned. Gear pumps are intermediate shear.

There is no particular problem operating centrifugal pumps at low speed provided you have a suitable driver.

Throughput with no resistance to flow is proportional to speed.

Deadhead pressure is proportional to the square of speed.

Power is proportional to speed^3.

To a first approximation, you can re-draw a manufacturers pump curve using these principles, or perhaps the MFR will provide you the information.

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Location: Mumbai, Maharashtra, India
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#6
In reply to #3

Re: Can a centrifugal pump be considered a low-shear pump?

11/05/2009 3:50 AM

So, whats the conclusion?

Centrifugl pumps at low speeds can be considered low shear pumps?

I want low shear centrifugal pumps for pumping produced water from LP seperator to a header before the Produiced water conditioning PAckage.

So if anyone has worked on it, kindly help me with your insights.

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DAKK
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#7
In reply to #6

Re: Can a centrifugal pump be considered a low-shear pump?

11/10/2009 4:29 AM

There is a general concensus rule within the manufacturers of oil / water separator systems for the oil indusrty that a cetrifugal pump operating at 4 pole speeds (50 & 60 Hz) with an efficiency greater than 70% and a generated head of less than 50 m per stage can be considered a "low shear" pump. Companies such as NATCO, Petreco (Cameron) and FLS Smidth gMAX work generally within these parameters.

There is a case study on the web at www.amarinth.com/.../Amarinth-case-study-B-Series-FLSmidth-supplied-low-shear-centrifugal-pumps-for-use-in-hydrocarbon-separation-module

Steve.

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#15
In reply to #7

Re: Can a centrifugal pump be considered a low-shear pump?

01/08/2011 4:01 AM

I am looking for low shear pump with 300m head.water cut varies from 20 to 90%.capacity 120 m3/hr. Can i get a quote.

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Location: Mumbai, Maharashtra, India
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#9

Re: Can a centrifugal pump be considered a low-shear pump?

11/10/2009 4:49 AM

Dear Steve,

Thanks for the reply. In my case even the client did not specify wether it should be a API 610 or API 676 pump. So the next step for me is to look for suppliers supplying such pumps.

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#10
In reply to #9

Re: Can a centrifugal pump be considered a low-shear pump?

11/24/2009 7:34 AM

I would be pleased to receive your enquiry if it is for an API610 pump.

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Anonymous Poster
#11
In reply to #10

Re: Can a centrifugal pump be considered a low-shear pump?

11/26/2009 1:26 PM

I have exactly the same scenario for which I need a low shear pump (pref API 610, but flexible).

Media: Produced water, 1-5 cSt, max 68 degrees C

Capacity: 15 m3/hr

Head: 113 mlc

NPSHa: 14 mlc
Pls email awf@fuglesangs.no with any suggestions.

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Anonymous Poster
#12
In reply to #10

Re: Can a centrifugal pump be considered a low-shear pump?

02/20/2010 12:26 AM

Can you provide quotation for 8 pumps for GASCO?

We need low shear centrifugal pump capacity 20 m3/hr , head 75m , Sp gr = 0.9

Vis = 10 cp Service sour water , slop oil pumps

Please send cross-sectional drawings. PL PROVIDE your at the earliest as it is urgent requirement.

My email ID : RBabu@gasco.ae

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Anonymous Poster
#16

Re: Can a centrifugal pump be considered a low-shear pump?

01/10/2011 3:35 AM

We have many applications where crystals in suspension, oily water, vegitables in water, carbon slurries, latex, live shell fish and sand slurries are being pumped with recessed impeller pumps that have hydraulic efficiencies of 50 to 60%

We even have applications in Asia and USA where we are pumping Nitrocellulose slurries!

The vortex pump handles such solids with very low damage or impact to the solids, we have some reports and studies that our customers have made concerning these pumps and in some cases have compared with competitors designs where hydraulic efficiencies are in the region of 70 to 80%

Impact to the solids or the liquid seems to be more of an issue than the hydraulic efficiency, in some reports it has been proven that more damage occurs in the pipework (bends) than throught the vortex pump. It is clear as with everything there are limits but so far we have been successful in what we have been pumping, for our Nitrocellulose applications, we have one specfic customer for more than 20 years.

For us the proof of having a low shear pump is having the experience and applications, we have such applications.

Ron

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Users who posted comments:

Anonymous Poster (3); crownvic (1); dakk (2); Dats (1); Elvis Chong (2); phoenix911 (1); PWSlack (1); Steve Buckley (3); Turo (1); Worksalot (1)

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