minimum/maximum flow as a function of the specific speed 2

Relationship is to % of BEP Flow.

See Attached;


"The top of the organisation doesn't listen sufficiently to what the bottom is saying." Tony Hayward X-CEO BP
"Being GREEN isn't easy." Kermit

wrong button,

here it is

"The top of the organisation doesn't listen sufficiently to what the bottom is saying." Tony Hayward X-CEO BP
"Being GREEN isn't easy." Kermit

Thank you, Biginch. The picture does look familiar, but it has been completed with some quantitative data and the bell-shaped graph. Would you really consider the 0,1*efficiency a good practice? It looks to me being a bit too far from the desired situation or am I misinterpreting the graph here?

Karel Postulart, The Netherlands
Nuon Power Generation

There is no efficiency on that chart. That's MTBE data.

"The top of the organisation doesn't listen sufficiently to what the bottom is saying." Tony Hayward X-CEO BP
"Being GREEN isn't easy." Kermit

We use minimum flow criteria that are based on specific speed and suction specific speed. We use a table that we generated ourselves. But, it is based on a figure in "Pump User's Handbook", Bloch and Burdis, 2004. This, in turn may be based on work by Val Labonoff. Our table defines a recommended reliability minimum flow but does not specify a maximum flow. I have attached a spreadsheet with our version of these criteria.

Johnny Pellin

That's interesting. Do you see any correspondence between the reliability curve and your figures, ie. should the general reliability curve be tightened up so the lower range matches your figures?

"The top of the organisation doesn't listen sufficiently to what the bottom is saying." Tony Hayward X-CEO BP
"Being GREEN isn't easy." Kermit

There are so many parameters to consider. It is difficult to make general criteria without being too conservative in some cases and not conservative enough in others. We use the criteria that I posted above for existing installations. But, if we are building a new system, we use even tighter criteria (more in line with the Best Practice line in the figure you provided). For most new applications, we require that the pump system be designed to operate the pump between 85% and 105% of BEP. For any existing single pump running alone, we would not normally allow operation below minimum stable continuous flow for more than a few minutes. For pumps operating in parallel, we would strictly require that they meet the minimum requirement in my posting above. And for new applications, we hold them to the highest standard. This inconsistency may seem strange. But, when building a new system, we can insist on the highest standard without adding too much additional cost. Once the system is built, it is difficult to justify the cost to upgrade to this higher standard. But, our experience with pumps running in parallel tells us that we must increase the minimum flow requirement or we are very likely to have trouble.

And, on top of all of this, we have to consider the service. A failure of a pump in 500 °F Naphtha is much more of a concern than a failure of a cooling water pump. So, for non-hazardous services, we are more likely to compromise. And, some things are just impossible to predict. We have pumps in our products blending system that are regularly operated as low as 10% of BEP, but are among the most reliable pumps in the refinery. And we have others that will fail quickly if they are operated below 80% of BEP. So, we set criteria and try to minimize the exceptions we grant. And, then we use Root Cause Failure Analysis and vibration analysis to identify applications where the criteria are not stringent enough.


Johnny Pellin

As a general guideline, the reliability based curves are idealistic and we know there are many cases, as you mention, where low range ops do not cause the any of the faults you would anticipate based on that curve alone. The suction speed variable looks like it goes a long way towards allowing a more reasonable application of the reliability curve to specific installations. I like it.

"The top of the organisation doesn't listen sufficiently to what the bottom is saying." Tony Hayward X-CEO BP
"Being GREEN isn't easy." Kermit

I did follow your discussion and I am quite pleased with the goven considerations and information. In the meantime I have found two things of which I will present one here right now. I got it from the german book Kreiselpumpen
(Springer Verlag ). It does indicate a limit for the minimum flow and the maximum flow as well.

Karel Postulart, The Netherlands
Nuon Power Generation

As I promised I enclose with this message another source of information, that deals with minimum flow with respect to avoiding the occurence of recirculation.

Karel Postulart, The Netherlands
Nuon Power Generation