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AFT Blog

Welcome to the Applied Flow Technology Blog where you will find the latest news and training on how to use AFT Fathom, AFT Arrow, AFT IMpulse, AFT xStream and other AFT software products.
Erin Onat

Inherent vs. Installed Control Valve Curves and How They Relate to AFT Software

As tech support engineers, we sometimes receive questions from users confused about what control valve characteristic curve (inherent or installed) they are inputting into AFT Fathom, AFT Arrow, or AFT Impulse. The inherent control valve characteristic curve plots the valve open percent versus the percent of maximum Cv. This curve is true regardless of the system effects on the valve. The installed control valve characteristic curve plots the valve open percent versus the flow through the valve, and this plot is dependent on the conditions specific to the system. For example, if the control valve flow setpoint is fixed at 250...
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Dave Miller

Tolerable Convergence

Trying to design and analyze piping systems can be a complicated, and difficult task for engineers. This was especially true before the advent of easily accessible computer technology. Hand calculations required hundreds of hours of painstaking work, by entire teams of people. Great care had to be taken to ensure the reliability and accuracy of the results. Human beings do make mistakes, after all.

In today’s engineering world, there are a multitude of computer tools designed to make the design process simpler, faster, and more reliable, such as AFT’s family of analysis products. AFT products revolve around graphically based, drag and drop interfaces that makes creating a computer model of piping systems quick, and easy. Being able to create simulation models with little effort, however, can be a bit of a double-edged sword.

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Erin Onat

Give me some details about Detailed Tees!

Frequently in tech support, when a difficult-to-converge model comes in, one of the first things we check is whether or not any tees in the model are being modeled as detailed tees. The reason for this is that the hydraulic calculations involving detailed tees can be complex due to the interdependence between velocity and pressure loss for each pipe connected to the tee. Iteration must, therefore, be performed to find a pressure loss and flow through each connecting pipe that agrees with the rest of the flow and pressure solutions in the model. This begs the question, then, what calculations are...
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Ben Keiser

What Does “Head (HGL)” Mean for Submerged Pumps and Exit Pressures?

In AFT Fathom and AFT Impulse, it is possible to model a submerged pump where a short and possibly frictionless suction pipe for the pump’s inlet does not need to be modeled.  When modeling a submerged pump, there are two options available for specifying the system inlet boundary condition at the pump suction.  As shown in Figure 1 below, the Submerged Pump’s Suction Pressure can either be specified as “Head (HGL)” or “Pressure”.   Modeling a submerged pump is not the only time where the “Head (HGL)” or “Pressure” choices will arise.  If an Exit Valve (i.e., a valve that discharges...
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Ben Keiser

Know Your Pump and System Curves - Part 1

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...
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Recent Comments
Guest — Tom MacWilliams
It would explain why flat curves are popular in HVAC
Saturday, 07 October 2017 23:06
Guest — Jerry
Such a great article this can really help a lot of people to decide what is the best for pressure equipment t
Wednesday, 26 September 2018 14:39
Guest — Dreamer
Amazing explanation.
Sunday, 09 December 2018 12:19
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Ben Keiser

When Should You Use Variable Pipe Resistance?

Have you ever finished running an AFT Impulse model and then received the following Warning message shown in Figure 1 and then wondered what it means? During a waterhammer analysis, the flowrates are constantly changing all throughout the system, therefore, the velocities and Reynold's numbers are also constantly changing.  The friction factors will also be constantly changing during the transient.  By default, AFT Impulse will use the friction factors that are obtained during the steady-state analysis and then use the same friction factors during the transient and they will be assumed to remain constant. Since it is possible for the flowrates...
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Erin Onat

Combining Pipes in AFT Impulse to Decrease Model Run Times: How Resistance Curves Are Merged into Pipes to Increase Pipe Section Length

They say that time is of the essence, and as engineers, that couldn’t ring truer! AFT pipe flow software is there to help engineers save time by more safely, efficiently, and rapidly designing and analyzing their piping systems. AFT Impulse, Applied Flow Technology’s waterhammer tool, helps engineers analyze transient incompressible flow behavior that can cause potentially detrimental pressure surges. It uses the Method of Characteristics, which requires the pipes to be sectioned using a Characteristic Grid. In this Characteristic Grid, all of the pipes are broken into an integer number of section lengths, and pressure waves are assumed to propagate through...
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Recent Comments
Ajay
Hi Erin, This method really helps to reduce the runtime of model but in some model like the one which i have with me has few small... Read More
Friday, 05 May 2017 06:37
Erin Onat
Hi Devendra, Thank you very much for your comment, and I'm very glad that you have found this blog useful. There is no way to ig... Read More
Monday, 08 May 2017 17:25
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