The Scope of Pump Reliability

The Scope of Pump Reliability

Thirty (30) some years ago I skimmed through an exhaustive study of the possible modes a prototype nuclear pump could fail and the probabilities connected with these events. In the report, the first reliability study I had seen, there was no discussion on how to influence or change failure probabilities. Absent a linkage to changing […]

Common Centrifugal Pump Terms in Plain English


The terminology of a technical subject is key to understanding it. The language of modern pump technology has evolved for well over a hundred years. During this period, meanings of terms have changed. Good definitions are sometimes difficult to find. In nearly four decades of experience I’ve located key terms and their useful meanings. In […]

Suction – It’s Not What You Think It Is

Upside-down glass of water

Suction is often defined as a force that causes a fluid or a mixture to be drawn into an interior space. Some dictionaries more accurately define suction as a force or condition produced by a difference of pressures.  Both definitions are correct. However, the first tends to support the illusion that suction is the action […]

Which pump engineering units do you use?

Metric and USCS mass equivalency

It was over 35 years ago when I began what was to become a career in pumps. The company was Byron Jackson, an American firm headquartered in Los Angeles. US Customary System (USCS) units remained prevalent within the company despite its international manufacturing presence and a growing global adoption of metric. Years ago there were […]

What is the connection between Suction Specific Speed and Minimum Flow?

Suction specific speed and inlet vane angle

The connection between suction specific speed Sω (NSS) and minimum flow (Qmin) is that, in general, a higher value of Sω (NSS) is associated with a higher value of Qmin.  Beyond that generalized statement, however, there is wide range of deviation and exception. For rotodynamic (centrifugal, mixed-flow and axial flow) pumps suction specific speed is the main […]

Critical Pump Selection Webinar – Video

critical pump selection three major issues webinar video

After the success of my webinar, I am making a recording of it available for everyone who was not able to attend, and those who wanted more time to go over the material and illustrations. Thanks again to everyone who attended the live webinar! If you want to hear about future webinars, subscribe now for […]

Centrifugal Pumps Second Edition – A Book Review

Centrifugal Pumps, Second Edition by Johann F. Gulich

The first pump text book I purchased when I began my career in pump engineering 36 years ago was Centrifugal and Axial Flow Pumps by A.J. Stepanoff.  At the time, in the US anyway, that book was considered an essential text on the subject for centrifugal pump engineers.  Gülich’s Centrifugal Pumps Second Edition is now today’s […]

Impellers – why underfile?

Underfile Performance Curve Chart

Underfiling is the removal of material from the underside (also back side, “non-working” side, or suction side) of an impeller vane at the inlet or the exit.  In this article, underfiling will refer to the exit.  The terms “underfiling”, “back-filing”, “S2 cutting”, and “Sv cutting” are equivalent.  There are probably others.  A related term is […]

Should pump users care about axial thrust?


Normally the user shouldn’t have to care about axial thrust.  Pump failure from an axial thrust-related problem is relatively uncommon.   But very few, if any, pumps are entirely immune to this class of problem. Why is this?   First of all, a rotating single-entry impeller wants to move in an axial direction and usually with lots […]

What is the Purpose of Minimum Flow?

Chart of pump phenomena and minimum flows

Over the years use of the term “minimum flow” has evolved.   Decades ago industrial centrifugal pump manufacturers quoted a single, relatively low value for minimum flow intended to prevent users from running their pumps to destruction.  The term “minimum flow” generally meant the lowest continuous flow the pump was permitted to operate, without reference to […]

Hydrodynamics of Pumps (2011 edition) – A Book Review

Hydrodynamics of Pumps, 2011

Hydrodynamics of Pumps by Christopher E. Brennen was first published in 1994.  Aside from my long-time professional acquaintance with the author, what caught my attention in this book are the various technical passages related to rocket propulsion turbomachines, including the Space Shuttle Main Engine.  Over the years I would hear about the technical issues with these […]

Diffuser versus volute


The stator section of a centrifugal pump, after flow exits the impeller, is usually either a ‘diffuser’ or a ‘volute’. The purpose of each of these two stator types is to efficiently diffuse velocity energy into pressure. Diffusers are characterized by a plurality of radially symmetric diffusing passageways surrounding the impeller. Either a volute-shaped or […]

Pump Handbook Fourth Edition – A Book Review

Turbine-Driven Mainline Pump: by Randal Ferman, Ekwestrel Corp

Years ago I owned a copy of Pump Handbook 1st Edition, by Karassik, Krutzsch, Fraser, and Messina.  While it was a book to have on the shelf, it was not my primary source of pump engineering reference material.  I obtained most of my pump technical information from other books and publications.  Eventually someone “borrowed” my […]

Horizontal or Vertical?


In selecting a pump for a given application there is sometimes the option of choosing either a vertical or a horizontal shaft pump arrangement. For instance, in a process plant certain product transfer applications might be performed by a can-type vertical pump, or a vertical in-line pump, or a horizontal process pump. Large capacity cooling […]

Specific Speed – Does it Matter?


To the pump engineer or pump manufacturer specific speed is terrifically important.  To the specifying engineer or user – maybe, maybe not. The term specific speed comes up frequently in pump literature, in technical papers and is always covered in pump text books.  It is frequently heard in pump technical banter and if one doesn’t […]

Is there any confusion about NPSH?

double suction pump profile

Net Positive Suction Head (NPSH) is perhaps the most misunderstood concept in pumping technology.  The main source of confusion stems from multiple uses of the term in different but related contexts. One usage of the term NPSH is to denote the suction performance characteristic of the pump itself, independent of the system into which it […]

Multi-stage pump in-line (tandem) versus opposed impeller arrangements


Common to early twentieth century multi-stage rotodynamic (centrifugal) pumps were design features for minimizing axial thrust.  At that time the thrust bearings available had limited load carrying capability.  Design solutions evolved in two principal directions. One design approach was to hydraulically balance the thrust for each stage or for the entire series of in-line (tandem) […]

The ideal pump

Turbine Driven Mainline Pump - photo credit Randal Ferman

Consider a pump that functions reliably under all possible operating conditions, no matter how abusive, including complete loss of prime or dead heading. Imagine this pump converts all of its mechanical work input into useful liquid energy output. Next, the seal or seals are zero leakage and require no flush, quench, or support system. The […]