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(Extremely basic) centrifugal pump design

  1. Jul 11, 2015 #1
    Alright everyone, I know this is a huge question, but I've done enough homework to at least have informed ignorance on the subject. I posted a similar topic here, but that question was more conceptual and this definitely is much more of an applied use question.

    (Edit: I realize that the above post was made on a newer account; issue of using multiple emails throughout the years. I may jump onto that account for replies for continuity purposes)

    I'm interested in designing an extremely basic, "proof-of-concept" centrifugal pump; it need not be energetically-efficient nor anything good enough to make it to a professional-level design; it simply needs to be able to supply fluid at the given flow rate and head that I need for the application, regardless of power input and efficiency (once I have a simple design, then I'll evaluate the feasibility). To make this somewhat easier, I'm willing to accept a wide measure of "tolerance" in the end specifications; it doesn't have to meet up. What I'm looking to gain out of this is the design practice, something I haven't been able to learn elsewhere.

    The reason why I decided to ask this here is that I've looked up many centrifugal pump resources, and I can't for the life of me seem to find a resource approaching them from a component-level design perspective. Most resources out there seem to be geared towards educating engineers or teams in the basics well enough to prepare them to be able to select the proper pump for an application, but no documents I consulted really broke down the design elements. I've found documents about impeller design (velocity triangles, etc.), but these don't account for the volute, of which I haven't been able to find any documents on. Even then, the impeller design docs I found don't tie the impeller specs in to the pump specs (head, flow rate, etc.) very well so even if I could make a simple impeller, I don't feel like I could make a very good pump. All of this feels like a very "black art" to me at this point.

    So, how would one go about designing a pump? Obviously, the operating conditions must first be quantified, so head and flow-rate, but how do these then get turned into impeller design considerations? I know the volute plays a role, but what is the math behind it? I suppose, if nothing else, I'm looking for some spirited discussion so that way I can know where to look better.
     
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  3. Jul 11, 2015 #2

    Baluncore

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    Centrifugal pumps are integral designs because all the parts must work together.

    Given an RPM, and knowing the maximum pressure required with no flow you can select an impeller diameter. Knowing the maximum flow at low pressure you can select an outlet diameter. Knowing the inlet pressure you can select an input port diameter.

    The pressure difference times the flow volume will give the power requirement and so determine the drive shaft diameter needed at the design RPM.
     
  4. Jul 11, 2015 #3

    SteamKing

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    The book Centrifugal Pumps and Blowers by A.H. Church (1944) is one of the classic texts on the subject. Second hand copies of this book are available thru distributors like Amazon.com or second-hand sellers like Abe Books. You can also use the book search feature at Amazon to find more modern titles on this subject if Church is too old.

    As far as I remember about my pump design class, no one cares about the volute, 'cuz it's there just to keep the water from spraying out of the impeller. The design of the impeller and the speed and power of the motor determine the flow rate and head you can obtain from the pump. Unless there are some unusual circumstances, I don't believe there are many people who do a complete, "clean sheet" design of a centrifugal pump. I think most pump manufacturers have designed enough impellers to suit just about any head-flow combination normally encountered in industry. There's probably not much new in pumps except for converting from paper drawings to digital CAD in the last 30 years or so. Maybe someone has studied CFD and pumps, but I'm not sure if the subject is advanced enough or the benefits of applying CFD to pump design are worth the effort.
     
  5. Jul 11, 2015 #4

    Baluncore

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  6. Jul 16, 2015 #5

    Nidum

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    The exit volute is there to allow some of the kinetic energy in water stream to recover into static pressure .

    Essentially the same as on CF compressor on gas turbine but technically less demanding .
     
  7. Jul 16, 2015 #6

    Nidum

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    There are three basic shapes for blading on the impeller - straight , back curved and forward curved .

    Each shape has merit for particular performance requirements .

    Since water is nominally incompressible the channels between the vanes need to be approximately constant cross section area with increasing radius so as to minimise cavitation problems .

    Ideally there would be inlet guide vanes and a curved lead in on impeller blades but many pumps omit these refinements .

    Ask more specific questions if you want to .
     
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