5 replies to this topic

[albrocky]

I am currently undertaking a project where i need to make a large number of pumps more efficient. i have so far been able to work out the efficiency of the pumps by using the flow rates, motor inputs, pump outputs, etc.

i would now like to predict how efficient the pumps could be if we were to make some alterations. one of the propositions was to lower the speed of the motor (this would lower energy consumption) and install a larger impeller. we believe this would keep the flow rates the same as they currently are, but at the same time it would lower the enery consumption of the motor, saving money.

my question is does anybody know of any equations or methods that i could use to relate the diameter of an impeller to the efficiency of a pump.

any help with this matter would be much appreciated.

[djack77494]

Refer to the pump affinity laws which relate impeller size, rotational speed, capacity, head, and other factors. But understand that the affinity laws have limited accuracy and work best when only small changes are contemplated.
Doug

[ELEMAN]

Hello everybody:

albrocky, I think this document can be of some help for you. http://http://www.driedger.ca/ce1_cp/CE1_CP.html

Good luck !

[Art Montemayor]

The URL furnished by Eleman doesn't seem to work.

If you are trying to get information from the Walter Driedger collection of control papers - especially the one on centrifugal pumps, then you can use: http://www.driedger.ca/index.html#home

I think that will get you there.

By the way, I don't believe that simply lowering the speed of the motor drive on a centrifugal pump (by increasing the number of poles on the motor driver) will lower the pump's energy consumption. The amount of energy that a pump requires to do a job is not dependent on the speed at which it runs. The speed may affect the efficiency, but not the energy consumption. One thing leads to another. Also, lowering the speed of a centrifugal pump doesn't necessarily make it more efficient. It all depends on the head and system characteristics of the hydraulic application.

Another good website to gather information on pump operation and efficiency is at: http://www.mcnallyinstitute.com/

An excellent site to read and learn about pumps, efficiencies, and pumping in general was www.fluidedesign.com. This is (was) Jacques Chaurette's website but I have not been able to connect to it. The website may be experiencing problems and that's a tragedy for young engineers. What you can do is use the Google search engine to find information on Jacques Chaurette and/or Fluide Design. You will find a rich quantity of information from Jacques on impellers, different types, different pumps, and their relative efficiencies - most of these articles and tutorials are in .pdf format and can be readily downloaded and printed out. I highly recommend you google for Jacques Chaurette and you will profit by it if you are serious about learning more about pumps and their efficiencies.

As a coincidence, both Walter and Jacques are Canadiens - and damn good engineers.

Good Luck and good pumping.

[pawan]

I will suggest using characteristic curves supplied by the vendor. They are the most accuarte tools to predict reslut of any modification.

If you do not have them, just try to construct at different speed or impeller dia by cosnidering small step changes. This will give you a no which can be analyzed based on uncertainity or sensitivity analysis for performance range.

[Chris Haslego]

Hello all,
Mr. Driedger contacted me and wanted to pass along with reply to this thread:

"I think your best gain in pump efficeincy may be in examining the circumstances in which the pumps are used to see if these are inherently inefficient. If the pump has a control valve at the discharge, check the typical position of the valve. If it is less than 60% open, perhaps your pump is simply too big. Energy savings will certainly result if you dump less across the valve. Another example is if you have a pump in on/off control. If it is usually off this means that it is oversized. Remember that a pump running 50% of the time at 100% flow will use four times as much energy as a pump running 100% of the time at 50% flow for the same amouint of integrated flow. That's a saving of 75%!

Walter Driedger"