All About the Self Priming Well Pump

A self priming well pump is simply a centrifugal pump that can be located above the suction reservoir with no need for an external priming system. It comes with an enlarged case that holds some liquid for supporting priming. It does not require a check valve whenever the liquid to pump is below the level of the pump. It does not also need to be primed so as to fill the suction pipe with water. Instead, it starts turning whether it has air or not. Nonetheless, it can never operate if there is no water. They are capable of handling a wide variety of liquids including solids, slurries, and even corrosive fluids.

How a Self Priming Well Pump Works

  1. Air enters the impeller and mixes with water during the priming cycle.
  2. The impeller through centrifugal action discharges the water and air into the water reservoir.
  3. The water sinks and the air rises.
  4. The water that is free from air and heavier, through the force of gravity, flows back to the impeller chamber. It is now ready to mix with more air that flows into the impeller.
  5. When all the air has been eliminated, a vacuum is created within the suction line. This ultimately pushes the water up the suction line by atmospheric pressure. That is how pumping begins.
  6. The water re-circulation within the well pump stops the moment pumping begins. If the pump is started later on, the pump automatically self primes. It will mix the water and air on its own so as to create a fluid that can be pumped.

Advantages of Self Priming Well Pumps

The self priming well pumps offer a great advantage when it comes to handling solid substances. They can handle solids of up to 3 inches. There is no single pump out there that can handle what self priming well pumps can.

The second advantage with self priming well pumps is that they are capable of continually pumping the fluid even if the pump is located outside the pit.

Disadvantages of Self Priming Well Pumps

The self priming well pump is at times inefficient since it requires a larger clearance for it to handle solids. It also needs a larger volute to facilitate self priming.

It also has issues that come up as a result of continuous usage. Most of the problems are encountered on the pump’s suction side.


A new self primed well pump should be subjected to priming before use. The process is clearly laid down on the manufacturer’s manual and therefore this should never be hard to conduct. The pump should also be primed once more after the initial priming. This guarantees maximum efficiency since various factors may come into play including fluid evaporation during initial priming.

A Final Word

You cannot operate a self priming well pump without water in its casing. A new self priming well pump that is out of the box will not begin to pump when turned on. To avoid seal failure, never try to use the pump when there is no water in the casing. The main difference between a self priming well pump and standard centrifugal well pumps lies in the ability of the former to retain water after the first priming.