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Answering Your Water Pump Questions

with RPS Engineer Mike

Can a pump be too big for a well? (4" in 4" casing")

You’ll routinely run across what's called a “4 inch” submersible pump, referring to the diameter measurement of the pump. But the name is misleading. A “4 inch” submersible pump is actually around 3.85 inches in diameter, which allows the pump to slide into a 4” well casing. Matching a 3.85” pump to a 4 inch well casing is totally normal and used widely within the industry, the pump WILL fit and won’t have any issues pumping water. 


The only times you might have a problem sliding the pump downwell, is if the well is quite old and the casing has shifted around, resulting in bending curves or protruding rock. This scenario is rare, and you’ll know immediately as you attempt to lower the pump downwell if there is a blockage. 

   

A pump can be too big for a well in a couple ways…


  1. Pump diameter is too large for the well casing 
  2. The pump produces a higher gallon per minute rate than what the well can produce 

Pump Diameter is Wrong


Submersible well pumps come in a variety of diameter sizes. Below is a chart of the diameter of pump fits in each type of well. 2” and 3” narrow wells can be found working with windmills in the middle and western United States, and shallow wells in states like Florida. 4” and 6” wells are common for residential and agricultural uses in all parts of the United States. 


2” Wells

3” Wells

4” Wells 

6” Wells

8” + Wells

2” Pump (2.01” diameter)

✅ 

✅ 

✅ 

✅ 

✅ 

3” Pump (2.9” diameter)

✅ 

✅ 

✅ 

✅ 

4” Pump (3.85” diameter)

✅ 

✅ 

✅ 

6” Pump (5.9” diameter)

✅ 

✅ 




The Pump Produces a Higher Gallon Per Minute Rate than What the Well Can Produce 


If you’ve sized the diameter of the well pump appropriately, the next step is to ensure that the well pump won’t over-pump your well. Your well report should detail the well production rate (how many gallons per minute is flowing into the borehole). A well that produces 25GPM generally shouldn’t use a pump that produces over 25GPM. Pumping over the production rate of the well stresses the well over time, and can actually lead to a diminishing well production rate.

Previous article How far from the bottom of a well should the pump be?
Next article How to DIY Install a Well Pump with Poly Pipe

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