These articles will help you understand how to use variable speed drives on pumps and when.

This book "Variable Speed Pumping, a guide to successful applications" by the Hydraulic Institute is excellent. This version is a summary of the book that is made freely available by The Hydraulic Institute on the web. The full version of the book is available on their web site

Another good book "Variable Speed Driven Pumps, best practice guide" by the British Pump Manufacturers Association (BPMA) is also made available freely on the web. You can visit their web site at

Another article is "Variable Speed vs. Constant Speed" by David Carrier and Ryan B. Stickney of the Plumbing Systems and Design magazine whose web site is at

Also see articles on variable speed on this web page: pumpworld.htm