Bo Gell is global product manager, wastewater, for Xylem’s Applied Water Systems growth center. Xylem has recently released a white paper on the importance of identifying the best efficiency point (BEP) for pumps in fountain applications. Mr. Gell sat down with MPT to correct some of the common misconceptions operators may have in pump selection and share insight from successful applications in the field.
MPT: What are some keys to selecting a pump that meets the specific requirements of the job and can stand up to the project’s demands?
Bo Gell: The first consideration is to ensure that the pump can run continuously and that it’s high duty rated, because not all pumps are. So when you’re selecting a pump, you need to make sure it meets that criteria. Another consideration is the heat generated by the motor and the dissipation of that heat is key.
In a fountain application, the pump is, generally speaking, submerged, and the ambient temperature of the water surrounding that pump needs to be considered. Even if the application is for a larger body of water—like, for example, a pond—it’s still important that the pump remains within the ambient temperature range. Many pumps might come with instructions stating that for continuous duty, the pump needs to operate in no more than 104 degrees Fahrenheit (40 degrees Celsius).
Also, the motor insulation classification is important. What that means is that the motor carries a certain insulation class. For example, Class S is a popular choice; Class B is a slightly lower temperature rating—about 266 degrees Fahrenheit (130 degrees Celsius); and Class F can handle temperatures that are a bit higher, 311 degrees Fahrenheit (155 degrees Celsius). Now, that temperature sounds very high, but that’s the internal temperature of the motor. But still think about how that heat needs to dissipate, because heat is the biggest killer of the pump and the motor.
MPT: How critical is it to rely on the manufacturer’s pump performance curve to obtain the maximum efficiency for a specific pump?
Bo Gell: Provided that the curve is correct, the main takeaway is understanding that the pump will always run along that curve. That’s a very important point for operators to remember: it doesn’t run off the curve, it needs to run exactly on the curve. So what that means is that the best efficiency point (BEP) is going to be somewhere in the middle of that curve.
A point to remember is that maximum amps will be when that pump is running on the right-hand side of the curve, or “max amps.” That’s not good. Now, the max amps is a specification found on the motor label, and with max amps in mind, what operators need to do is make sure the pump is not running at that level. Max amps is going to equate to the maximum heat, which is also going to equate to losses in terms of the pump’s being able to run.
Ideally, operators want to extend a pump’s life to its maximum before failure, and that’s why finding that best efficiency point (BEP) and striving to be somewhere near it, as opposed to nearing max amps, is so critical to the life of a pump.
MPT: What are some of the common pitfalls you see pump users find, and what are some methods to move flow back closer to BEP?
Bo Gell: The biggest issue with most fountain pump applications is that there typically is not as long of a discharge run, which means that the total dynamic head (tdh) is going to be very low. What that means is that the pump is running near open flow, so that ties back into running far back on the right-hand side of the curve: max amps and max heat.
The way that operators can reduce that is by reducing the discharge. Now that can be done with any kind of a valve, but it’s also a simple process to check the pump in the field to make sure you’re keeping it off the max amps. Remember, the max amps is on the label, so if you were to measure the current of the pump while it’s running and then throttle back the discharge, you can see how that pump then will move from max amps—if it’s near open flow—back to somewhere near the middle of curve. ◆
____________________________________________
MODERN PUMPING TODAY, February 2017
Did you enjoy this article?
Subscribe to the FREE Digital Edition of Modern Pumping Today Magazine!
How to Keep a Fountain Pump at BEP
