Pump Efficiency Study


I'm tring to run a energy cost scenario and need confirm how to insert efficiency points. 

One of the pumps it's a KSB 125-080-200, with rotor 190. 

I have uploaded the efficiency curve as it follows:

I'm considering the n [%] as the efficiency percentage corresponding to the determinated flow, just to confirm it's that right?

I also have a well pump:


How do i input efficiency points on this one? 

  • Since this is not a technical support question I have asked my colleague to take a look and provide insight if possible to help you.

    In the meantime: when you say "rotor 190" does that refer to the speed of the pump? The different curves shown in your first diagram may be for different pump rotational speeds, but I am not certain if the chart is trying to show the efficiency for the "n%" values. I would suggest asking the manufacturer for clarification if unsure.

    As for the well pump, I cannot read it and would similarly suggest asking the pump manufacturer for clarification if unsure.

    Other Community members may be able to interpret or confirm based on their experience with similar diagrams.


    Jesse Dringoli
    Technical Support Manager, OpenFlows
    Bentley Communities Site Administrator
    Bentley Systems, Inc.

  • The first pump curve for a KSB Megabloc 125x80 - 200 is for a pump with a single stage impeller.  In this particular model of KSB pump "125" is the flange diameter in the pump inlet = DN125 (mm),  "80" is the flange diameter of the pump outlet = DN80 (mm).   "200" is the nominal size of the maximum diameter impeller ("rotor") that can be fitted within it's pump volute.

    As the customer can order custom size impellers.  On this pump model KSB has differently sized impellor / rotor castings that can be lathed down to the size the customer wants, and then this in turn determines what maximum power rating is needed on the separate motor needed to swing this impeller.

    Usually the pump manufacturer will plot the full Flow vs Eta/Efficiency curves on the pump curve technical datasheet, but in this case KSB has used an abbreviated form where they only marked of with "tick marks" the points of different efficiency curve values where the intersect with the Flow vs Head curve, in units of %.

    As this process of using different castings or lathing those castings changes the impeller vane curve angles and the distance between the impellor perimeter and the fixed dimension outer pump volute casing, then there are different efficiency curves for each impeller size/diameter option, and when manufacturers plot full curves rather than just the points the curves intersect on the flow vs head curve, this becomes more apparent when visualised this way.  For example, here is similar single-stage pump with the full efficiency curves plotted against different impellor size options:

    The second pump has, unlike the first pump, a multi-stage impeller ie. Pump Head is added by the first impeller, where the flow exits to the inlet of second impeller to get more head added, which exits to a third impeller ,,,,  etc. etc.  Multi-stage pumps were historically used in Relatively high head vs low flow situations,  such as the very high lift heads needed from wells / bores.

    The "19" etc. on the pump curve is representative of the number of impeller stages, sometimes it is a number that is the actual number of stages, and other times it is a manufacturer internal model code for the number of stages, and the diagram itself is for completely separate models of pump, and each model variant physically changes how long the vertical pump volute chamber is, and the length of the impeller shaft, whether it needs to have 1, 2, 3 .... n impeller stages fitted within it.

    On vertical multi-stage pumps like this, the impeller "rotor" diameter is usually fixed and cannot be changed.  Instead the flow vs head curve is changed by adding or subtracting impeller stages, each stage with a fixed diameter impeller,

    Most often on multi-stage impeller charts like this that cover different model variants, the Pump Eta / Efficiency vs Flow is not plotted, and it isn't plotted here.   The way this is usually documented for multi-stage pumps is instead in supporting Tables in a pump manufacturer supplied pump technical manual.   There are exceptions, Grundfos was the first mainstream manufacturer to go to an all digital catalogue, first with WinCAPs (they sent you a CD-ROM instead of a paper manual) and then moved it to the internet with WebCAPs.  On their digital catalogue, it narrowed it down to which variant of multi-stage pump you had selected and would plot a single pump head vs flow curve, and an efficiency vs flow curve on the same digitally calculated-on-the-fly diagram.

    Examples though of paper copies of what is typically done for Vertical Multistage Pumps.  Eg. Davey Pumps does like this, making it "easy to read a Graph of Eta vs Flow

    ...whereas Caprari pumps on their Multistage units make a more "hard" to read catalogue.   This is not a graph of a curve but instead tables of Flow vs Head vs Power.

    Harder still in that they leave the engineer to work out Eta(%) themselves.   You have to spreadsheet this data from Caprari and then use the formula below to get the values needed to put into Eg. Models or engineering calculations.

    Eta (%) = Fluid Power / Shaft Power (P) x 100  where Fluid Power (kW) = Q (m3 / s) x Fluid Density (kg/m3) x g x H (m) / 1000

    For me, if the manufacturer didn't have the information published online, I always just emailed them or phoned them to get it, and usually had a reply within 1-3 working days.   Same for pump moments of inertia where pump manufacturers won't bother publishing it for the very small group of engineers who want this for transient analysis, but will supply it on request.

    Answer Verified By: Fabio Lobo Araujo 

  • I have a lot of material on pump efficiency studies. Send me your email and I'll send you some things.

    You can start with this blog post


  • I didn't expected so many information! That's pretty awesome! Thanks for all the help! I've just emailed the manufacturer! Thanks Ben! This helped a lot!