January 2010, Vol. 22, No.1

Extra

Hydraulic Forces

Straight talk about the split between operations and engineering

Randy Rosbury

During my nearly 20 years in the wastewater industry, I have worked as an operator and as an engineer. I started out managing and maintaining pump stations. Over time, I learned more and more about hydraulics, which are so important to the effective and efficient use of pumping within the industry. About 13 years ago, I began performing quality assurance reviews on the designs of pumping systems.

As I moved from an operations to an engineering perspective, I realized that when it comes to hydraulic modeling, there’s a big split in how these two groups see things.

My experience taught me that hydraulics is a science, but not an exact one. If a system is designed to perform at a particular point on a system curve and during installation something in the field changes that system ever so slightly, the performance will be changed.

Common sense, you say? Well, let me tell you, in the operations community, those performance changes are a way to put an engineer in his or her place. I can hear it now: “You said that pump would pump 2000 gal/min and it only pumps 1990 gal/min. Stupid engineer!”

I can’t tell you how many times I have heard just that.

This confrontational attitude leads to two problems. First, many engineers dismiss the fact that some operators, while they may not be able to explain Hazen–Williams equations or Young’s Modulus, can “feel” when a pump isn’t running correctly. Second, many operators dismiss the fact that designing hydraulic models requires some art, as well as science.

I don’t tell you this because it is news or to change human nature, just to ratify what many of us understand but won’t say. This type of relationship is counterproductive and doesn’t benefit anyone, especially the company or utility you work for.

An Operator’s Touch

Some operators can sense when something isn’t right with a pump, just as my wife can look at our children in the morning and tell they’re not feeling well. She may not be able to tell me exactly what is wrong, but she can certainly tell me something isn’t right.

To many operators, their equipment is their baby. They look at it, listen to it, and feel it operate every day. They know when something isn’t as it should be.

Many operators realize they have a knack for this and resent engineers that dismiss them, so they will take any opportunity to “put them in their place.”

Years ago, when I was on an operations staff, I mentioned to the design engineer that a set of pumps didn’t sound right. I was dismissed because he had measured the pressures and the flows, and he said the pumps were working as designed.

To make a very long story short, after three rebuilds during the first 5 years of operation and a cost in the tens of thousands of dollars, the station was re-examined and several design issues were found. They have since been corrected, and now the station performs as designed. It also sounds right.

An Engineer’s Practice

Now, after nearly two decades in the wastewater industry, I have wound up performing hydraulic modeling. Modeling is essentially putting electrical, hydraulic, and operational experience into a graphical representation of hundreds of mathematical formulas — a move that in the operational world often is considered a worthless endeavor.

It took me 18 months and hundreds of hours working with trained modeling consultants before I considered myself even halfway proficient working with and understanding models. Now, I consider myself fair, and only fair, at it. There is so much to learn, and as soon as you learn it, the industry evolves and there is more to learn.

One day, I had the opportunity to perform some quality control work on a force main that I was familiar with. A consultant had performed the initial modeling.

Initially, I found a great deal “wrong” with this model. Variations in elevations? Wrong. Pipe sizes? Wrong. But I asked myself, am I still in that old operator mode and looking to “put that engineer in his place”?

So I dug a little deeper. As I examined each “error,” I tried to think of why it might have been designed that way. Why would the modeler do that? What would the result of those choices do to the overall model?

Then it dawned on me. Each software program has its own capabilities, and each modeler has his or her own capabilities. Something I had been told by a consultant I had worked with before came to my mind. He said, “Sometimes, you have to fool the model” — “creative license,” as he called it. Of course, that creative license has to be verified, validated, checked, and rechecked, but it is the means to an end.

If software won’t calculate a 36-in. (900-mm) valve that is partially closed, the modeler might fool the model by telling it that the valve is a smaller pipe with the same restriction. Obtaining the desired result justifies some creative license.

But, when the next person takes a look at the model, depending on his or her mindset, that person may say, “There isn’t a smaller pipe in that force main, so this is wrong.”

So there is a little art to modeling after all, and if everyone understands that, we are better for it. I called the modeler that made the “errors” on these models and asked about them. Most were creative license, as I thought, and, yes, a few were true errors.

Finding Middle Ground

The moral to these stories is this: Let’s give each other some respect for what we each do well.

Operators, don’t dismiss the models that engineers make because the model doesn’t match how things look in the field; instead, insist that the engineers explain why they modeled things in such a way. You might be very surprised at what new tricks you can learn when you look through a new set of glasses. You may discover that this newfound tool can help you a great deal with your operational strategies.

Engineers, don’t dismiss an “old dog” who tells you something doesn’t sound right. Just because your spreadsheet and your model say it is right doesn’t mean that the creative license we use in the models didn’t miss something.

 

Randy Rosbury is a planning manager and modeler in operations and infrastructure support for the Department of Water Resources in Gwinnett County, Ga.

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