Submersible pump runs but does not pump any water

Imagine that you immerse your old or new submersible pump in water and turn it on. You hear it running, but it does not drain any water from the space. What is going on here, and how can you solve the problem?

Air in the pump body

When a submersible pump is immersed, water runs into its pump body, which is fitted with an impeller. The impeller ensures that water is transported from the pump body to the pump outlet. When a pump is placed in water, the pump house first fills with air,  which replaces the water. However, not all air will automatically exit the pump house. A submersible pump can only operate optimally when no air is in the pump house. Air is lighter than water and will always sit at the top, where the pump's impeller is situated.  A small amount of air renders the impeller unable to process any or only very little water, meaning that no water is being drained.

The solution

This problem is easy to solve. Let the air run out of the pump body, which is then replaced with water, and the pump can start operating. This is done by tilting the pump underwater.