AFT Blog

Any time a rapid transient occurs in a piping system, there is a chance for unexpected surge to impact the system. Though system shutdowns account for many surge events, pump startups can cause water hammer as well. For this blog I am going to cover the basics of setting up pump and valve transients for the startup case in AFT Impulse 7 , as well a...

The pistons, or diaphragm of a reciprocating (positive displacement) pump causes a cyclical variation, typically in some sinusoidal form, of both flow in pressure in a piping system. The magnitude varies, depending on the type and design of the pump. What is acceleration head?  Acceleration head is the energy required to change the velocity of the liquid in the system from an at rest, or zero condition, to some non-zero value. To help us understand acceleration head a little more clearly, you could compare it to a race car. In a drag race, the race car will accelerate to some maximum...

What comes to mind when you hear the expression “planning for failure”? For some, it carries the negative connotation that failure is the direct result of a design – intentionally or otherwise. Benjamin Franklin said; “If you fail to plan, you are planning to fail!” and I believe he would agree that any good plan addresses potential failures. In fact, not "planning for failure" as an element of a system is essentially failing to plan and therefore inviting unexpected and unmitigated failures. Life Cycle Cost One of the many reasons to avoid failure when possible is to reduce cost. When a...

Cutting through the mysteries of impeller trimming Centrifugal pumps are a common and integral part of many industrial applications related to fluid flow of any kind. They require significant amounts of energy to operate. Unfortunately, many pumps are oversized for their applications. When pumps are not properly sized this can lead to operational difficulties that must be addressed. A pragmatic solution to this problem may be to reduce the outer diameter of the pump impeller to better meet flow requirements and avoid costly operating procedures such as throttling or expensive replacements. Changing the impeller diameter will affect the performance of the...

Cavitation is an important subject in piping systems. Quite often, cavitation is an operating condition that is to be avoided, such is the case with pumps. Not only can cavitation cause serious decreases in pump performance, but it is also a maintenance nightmare if left unaddressed. Such issues are costly and may lead a system to be deemed unsafe. As you are likely aware, cavitation exists when the local pressure falls below the vapor pressure of operating fluid. Overtime the pressure may increase again so that the cavity formed then collapses. When this collapse occurs on the vanes of a centrifugal...

This past week I and Jeff Olsen, AFT’s V.P. of Technology, attended the annual conference of the Hydraulic Institute . The Hydraulic Institute (HI) was founded in 1917 and is America’s premiere pump organization. At this year’s meeting HI held a centennial celebration . For a technology organization like HI, 100 years is quite a feat and was rightly celebrated at the annual meeting this year. Many of you are familiar with HI through the standards HI creates. These standards show up in AFT Fathom in several places: Intake design  (pump submergence to avoid vortex formation) Pump viscosity corrections Slurry pumps...

AFT Fathom can easily generate a pump and system curve for your piping system.  Creating a pump and system curve for a simple system with a single flow path and no control features is an easy and typically well-understood process.  However, as piping systems are quite complicated with lots of branch points, control features, and dynamic interactions, creating a useful system curve can quickly become a common source of confusion.  This three-part blog series is going to help clarify concepts regarding pump and system curves to better understand them.   This Part 1 blog will discuss the basics of what pump...