You've placed a new or old submersible pump in water and turned it on. You hear the pump operate, but the water is not drained from the room. What's going on and what can you do to resolve this issue?
Air in the pump housing
After you placed the pump in the water, the water enters the pump housing. The pump housing also contains the pump's impeller. This impeller ensures that the water is transferred to the pump outlet.
When initially placing a submersible pump in water, the pump housing is filled with air. The air is replace by water once the pump is submersed. However, it is not necessarily the case that all the air leaves the pump housing once the pump is submersed. A submersible pump can only (optimally) operate when there is absolutely no air in the pump housing.
Air is lighter than water and will always move to the top of the pump housing. And it is precisely here where the impeller is located. Even a small amount of air prevents the impeller from working properly, which may make it impossible to drain water.
The solution to this problem is simple: make sure all air escapes the pump housing. As a result, the water will fill the entire pump, allowing the water to be drained properly. You can do this by tilting the pump under water. See the video below.