Subject: Pumps installed in pits. How to correct some existing suction problems. 14-12

Vortexing at the pump suction looks like a whirlpool of liquid in a sump or pit and sounds a lot like cavitation. Vortexing will cause a loss of the pump's capacity and excessive pump shaft deflection that is harmful to:

One way to tell the difference between a cavitation or vortexing problem is to remember that vortexing problems are intermittent as the vortices form. Cavitation once started tends to stay with you. Proper pit design can eliminate this vortexing problem, but what do you do if the installation is not new and the problem already exists? There could be several things that could have caused the recent vortexing problem:

Maybe the original design was bad and that is causing the problem. Although this is a very large subject there are a few guide lines you might check out:

Now we will take a look at what you can do with an existing installation. Remember that a low velocity and straight line flow to all pumps is always desired. If you are getting vortexing problems you might be able to:

In the next few illustrations I will show you the recommended sump dimensions to prevent vortexing and eddy flows. The first chart shows the recommended dimensions:

The next two charts show where the dimensions came from:

  • Dimensions "Y and A" are recommended minimum values. They can be as large as desired but should be limited to the restrictions shown on the chart.
  • If the design does not include a screen, or if the channel has a sloping approach, dimension "A" should be up to two times as long.
  • If the channel approach has a down slope the angle should not be more than 15 degrees

 

 

  • About the screens:
    • The screen or gate width should not be less than "S".
    • Heights should not be less than "H". 
  • Use dimension "S" for the width of an individual pump cell, or the center to center distance of two pumps if no division walls are present.

 

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