SUBJECT: Another look at dynamically balancing the pump rotating components 9-1

Everyone agrees that balancing the rotating components of a centrifugal pump is a good idea, but it's seldom done. Evidently it doesn't appear to be too important or it would be receiving some sort of priority when the pump is being overhauled or rebuilt.

To understand the importance of dynamic balance, visualize yourself going down the highway in your automobile at sixty miles an hour, and you throw off a small, lead wheel weight. Suddenly you notice a severe vibration in the steering wheel that makes you feel very uncomfortable. Do you have any idea how many rpm's the wheels were making at sixty miles an hour? Do you think it was slower or faster than the rpm of your centrifugal pump? Let's figure it out in the inch size and then we will do it in metric:

A typical fourteen inch automobile wheel has a tire that is approximately twenty five inches in diameter. This means that the circumference of that tire is 25 inches times 3.14 (pi) or 78.5 inches. Divide the 78.5 inches by 12 and you get 6.5 feet for the circumference of the tire.

At sixty miles an hour you car is going a mile a minute or 5280 feet a minute. Since the 6.5 feet represents one revolution of the wheel we divide that into the 5280 feet and we get 812 rpm at sixty miles an hour.

A typical metric tire would have a diameter of 635 mm. Multiply that by 3.14 and you would get just a little bit less than two meters for the circumference. At 100 Km/hr you would be going 1.7 Km or 1700 meters/ minute. 1700 divided by two meters for one revolution of the wheel is 850 rpm.

This means that if a small lead weight can become that significant at 812 rpm or 850 rpm what does an out of balance shaft in your pump do at electric motor speeds? Several things:

What causes a pump shaft to go out of dynamic balance, assuming it was balanced at pump assembly?

Balancing the Impeller

If you send the rotating assembly to an outside vendor for balancing be aware of several potential problems:

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