3 replies to this topic

[arundhamodharan]

I've been thinking about a problem that comes up when working with older pump data: you have a manufacturer's performance curve from an old project, catalogue, or paper document, but the original digital data is no longer available — and sometimes the OEM product line itself is no longer active.  

The curve may still be perfectly useful, but you're left with a scanned or paper Q-H curve rather than a digital dataset.

Curious how others here deal with this:

• Do you digitize the curve manually and recreate the Q-H data in Excel or another tool?

• How do you handle interpolation between the published points?

• When the operating conditions change, how do you generate a revised curve using speed or impeller diameter changes?

• For old curves, how do you handle efficiency and NPSHr data when only the original plotted curves are available?

• For pumps in series or parallel, do you digitize and combine the curves yourself?

I've ended up building an Excel workbook for my own work that takes a pump performance curve from a paper/PDF/image source, converts it into a usable digital curve, and then allows the curve to be evaluated under changed operating conditions using the relevant scaling relationships. It also allows the resulting performance data to be generated in a usable engineering format.

The reason I built it was mainly to make older or otherwise inaccessible pump curves usable again — particularly where the original OEM digital selection software or product database is no longer available.

Happy to share what I developed if anyone is interested. I'm mainly interested in how others here approach this problem and whether there are established methods or tools that you use.

[Pilesar]

I found Engauge Digitizer free software very helpful for digitizing pump and compressor curves. There are other digitizers out there, but this had everything I needed. One of its great features is the ability to digitize graphs even when the x and y axis are not at 90 degrees! Sometimes the old copies are warped or wrinkled and Engauge Digitizer does a much better job interpreting than my eye-brain combo. See more info here: https://engaugedigitizer.com/
 

[arundhamodharan]

Thanks for sharing that. I have been using WebPlotDigitizer (automeris.io) for this type of work and have found it very effective for extracting pump curve data from scanned catalogues, PDFs, and older paper documents.

The computer vision-assisted approach makes it fairly quick to calibrate the axes and extract Q-H, efficiency, power, and NPSHr curves into a usable digital dataset. I've also found it helpful when dealing with older OEM curves where the original selection software or digital records are no longer available.

 

One advantage is that it's web-based and handles a wide variety of graph formats without much setup. After digitization, I typically export the data to Excel where I can perform interpolation, affinity law calculations for speed or impeller diameter changes, and develop revised performance curves for engineering evaluations.

 

I'm also curious whether anyone is using tools that go beyond digitizing the original curve and can automatically generate or re-rate new pump performance curves from the extracted data (for speed changes, impeller trimming, series/parallel operation, etc.). I'd be interested to hear what software or methods others have found effective for that part of the workflow.

[Pilesar]

The major steady state process simulators allow pump curves as inputs so I never developed my own software tools for pumps. Determining fluid properties and hydraulic system requirements seemed more important than the pump design itself. I did not specialize in pumps. I usually determined impeller sizing by visual interpolation from the graphical curve for simple systems if needed. Usually I just selected the 'large enough but not too large' pump and confirmed that the system did not require a full-size impeller. I had a good relationship with a reliable pump expert who worked for the pump supply company. He enjoyed helping solve complicated pump system problems and I was glad to steer business to him. While I could specify impeller size for pumps, I deferred to his expertise and usually just delegated the impeller sizing to him for simple pumps also.