Electric motors have had a huge impact on the pump industry.
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Improved motor starters help Fabri-Kal achieve its green vision.
Facts can be tough—our emotions may get in the way. What we think we know is not always factual but is based on what we may intuitively feel is an undisputed truth. It is human to expect everyone else to agree with us, regardless if we truly know the facts or just think we do. And if others do not agree, then we think they are incompetent. Many people feel that all pump vibrations are bad, but is this a fact or only what we think is true?
Water and wastewater systems in the United States use a tremendous amount of power. The EPA estimates that these systems use 50 trillion watt-hours annually at a cost of $4 billion. Combined with electric rate increases upward of 20 percent in a single year, water and wastewater system operators are left with an enormous strain on their budget.
Mechanical resonance occurs when an external source amplifies the vibration level of a mass or structure at its natural frequency. For a rotating mass like a motor or a pump, this occurs at the critical speed(s). Electrical resonance amplifies the magnitude of voltage or current, or both.
Couplings are often forgotten until a project is nearing its end. With time running out, users often purchase whatever a supplier has in stock instead of the best solution for the system. Understanding the application and requirements for coupling selection allows the user to select the best coupling solution.
A paper or an electronic work order system can be used to capture alignment data.
An argument in favor of IEEE-841's provision for motor bearing protection.
In June, 2007, a reader asked Electrical Apparatus magazine, "How long should motor bearings last?" The answer will astound you:
"If (and it's a big if) ball bearings are kept clean and properly lubricated, their average or L-10 life should be 3 ½ centuries-3,180,000 hours."
Shaft failures do not happen everyday, but when they do, it can be a challenge to determine the cause of failure. Here's a technical explanation of what happens when the shaft bends or breaks.
Last month, we ended with a discussion of the relationship between peak and RMS (or effective) voltage. We found that the RMS voltage will always be 0.707 that of peak voltage, and peak voltage will always be 1.414 that of RMS voltage. This relationship holds true regardless of the sine wave frequency. But, as frequency changes, the total voltage applied to a circuit per cycle can differ substantially. To visualize this difference, we will need to introduce another unit of measure-volts per hertz.
Latest Motors Articles
Electric motors have had a huge impact on the pump industry.
Improved motor starters help Fabri-Kal achieve its green vision.
The industrial motor world has a new specification available for defining the requirements of general purpose, severe duty motors in the 250- to 3,000-hp range.
Proper alignment of the pump shaft with the driver can reduce vibration and significantly improve reliability. For appropriate applications, the time, expertise and instruments needed to achieve precision alignment (tolerances of less than 0.005 in) will prevent seal leakage and extend bearing life.
Introduced in June 2010, Super-E Motors with AEGIS Shaft Grounding Ring are used in commercial and industrial applications to drive pumps provides a path to ground for circulating currents, preventing bearing fluting.
A paper or an electronic work order system can be used to capture alignment data.
Last September, we spoke about the importance of pipe-to-piping alignment, evaluating actual numbers, and tabulating stress values as they approach yield stress of pipe at various values of misalignment. This time, we will discuss the effects of pump-to-motor misalignment, beyond hype or generalities, by numerically quantifying the conclusions.
A number of choices are available when connecting pumps, fans and other rotating equipment to an electric motor. There are numerous mechanical and fluid coupling designs and, in some cases, a belt drive option is available. Although a belt drive can be more forgiving, all mechanical couplings share the requirement for precise alignment. Since couplings provide a direct physical connection between the motor and the rotating machine, misalignment will create vibration and other stresses that can lead to premature coupling, seal and bearing failure. Misalignment can be due to poor alignment practices or suction and discharge piping stresses.
Editor's Note: Click here to see a sample alignment data form.
Proper alignment of the pump shaft with the driver can reduce vibration and significantly improve reliability. For appropriate applications, the time, expertise and instruments needed to achieve precision alignment (tolerances of less than 0.005 in) will prevent seal leakage and extend bearing life.
Columns and Blogs
In this multi-part series, we will investigate several aspects of centrifugal pump efficiency.
First of Five Parts
Since the original publication of this draft standard in the January 2008 issue of Pumps & Systems, I have received feedback, encouragement, numerous questions and criticism. The draft listed three basic levels of repair.
The McGraw-Hill scientific dictionary [5] states that a volute is "a spiral casing for a centrifugal pump... designed so that speed will be converted to pressure."
