Net Positive Suction Head: NPSHR and NPSHA
Addressing Net Positive Suction Head (NPSH) and its relationship to cavitation
Motor Horsepower & Torque Versus VFD Frequency
My January 2013 Pumps & Systems’ column focused on the reduction in motor horsepower (HP) as frequency is reduced by a variable frequency drive (VFD). I had several requests to revisit this...
Pumps & Systems, February 2009If you think hydraulic theory can be a tricky subject, consider the contemporary branch of physics known as string theory. It attempts to explain all of the...
Editor's Note: This is the second in a six-part series on centrifugal pump efficiency. For other articles in this series, click here. Early centrifugal pump design was heavily influenced by turbine...
A number of choices are available  when connecting pumps, fans and other rotating equipment to an electric motor. There are numerous mechanical and fluid coupling designs and, in some cases, a...
I hope that my last column (Pumps & Systems, September 2014) provided a clearer definition of power factor and how it can be calculated. Power factor can also be explained using a vector triangle, but...
For those of you old enough to remember Lawrence Welk, you’ll notice that the title of this brief column is the final quote from his show’s closing song. I am still a loyal fan of his reruns...
In my last column (Pumps & Systems, October 2014), I explained that a capacitor’s current is totally out of phase with that of a motor’s magnetizing current. This allows the capacitor to store...
In my July 2014 column, I demonstrated that three-phase voltage variation can significantly affect several alternating current (AC) motor characteristics. If that variation is large, it can also...
In my June column on pump and motor testing, I said that three-phase voltage variation and unbalance can have a significant effect on motor insulation life. Voltage variation is defined as the...
Pumps & Systems, June 2007Most of the electric motor information we use on a daily basis is pretty straightforward. Voltage, amps, efficiency, and service factor are all well understood terms in...
The Bernoulli Principle
Read Part OneRead History of Pumps seriesThe Bernoulli Principle explains the flow of fluids and was one of the earliest examples of conservation of energy. It states that during steady flow, the...
Many publications discuss the causes and cures of cavitation, but few address the reason those bubbles are so destructive. Boiling is the precursor to cavitation in a centrifugal pump. Boiling is not...
"Testing Centrifugal Pumps in the Field,” Pumps & Systems, February 2011, featured an Excel spreadsheet designed to simplify the field test procedure. The equation for total dynamic head (TDH)...
This article is part of our ongoing series on The History of Pumps. During the past few years, I have written articles about scientists who have contributed to our understanding of hydraulics....
In 2011, I wrote a five-part series on alternating current (AC) motors and motor efficiency. This column will go into more detail about the impact of efficiency. Efficiency defines how well a motor...
Memorization and learning are two different things. As I look back on my own education—formal and real life—most of the facts and figures that I memorized are long gone. Even today, routine...
Editor's Note: This is part one of a three part series about variable speed pump selection. To read the next article in the series, click here.When it comes to pressure and flow, variable speed...
Today’s federal requirements dictate the minimum efficiency of an electric motor, but they do not have any impact on the efficiency of a centrifugal pump. A 10-horsepower, 1,800-rpm motor must meet...
First of Two Parts Branch-line pumping applications abound throughout the pumping industry. These systems consist of a pump (or pumps) discharging into a single line that feeds a network of...
Last year, a Pumps & Systems reader asked about matching variable frequency drives (VFDs) and motors. “I have a spare pump in my warehouse that requires 15 horsepower (HP) at best efficiency...
Pumps & Systems, August  2008In part one of this two-part column, we will define water hammer and explore the events that cause it. We will also try to gain perspective on the additional...
In my opinion, the system curve is the single most important component of the pump selection process. After all, the system curve determines the operating point on a pump’s performance curve. Other...
In the February 2010 issue of Pumps & Systems, I discussed my Suction Specific Speed (S) Calculator and its ability to predict the stable range of flow for a particular centrifugal pump. In November...
The Life and Work of Daniel Bernoulli
Editor's Note: This is the first article in a two-part series on Daniel Bernoulli. The series is part of a larger ongoing series on the history of pumps.Have you ever noticed that the pressure...
Breadth of Efficiency
In 2012, I wrote a six-part series on centrifugal pump efficiency. In Part Five, I touched on the importance of the breadth of efficiency and how it can be more useful than the peak best efficiency...
Why Wye? Why Delta?
Pumps & Systems, July 2013Second of Three PartsThe secondary configurations reviewed in Part One (Pumps & Systems, June 2013) are typical three-phase configurations found in pump applications....
Why Wye? Why Delta?
First of Three PartsOne of the more confusing elements of three-phase power is the winding connection schemes for inductive devices such as transformers and motors. Although most of us with a basic...
Three Fictitious Forces & One Real Force
Pumps & Systems, April 2013Two schools of thought exist with regard to centrifugal force. The one I support views it as a false force. The other side believes that it is real. That is the side...