Submersible well pumps are multistage centrifugal pumps. Each stage consists of a stationary diffuser and a rotating impeller. Submersible well pumps usually work in a vertical position and the impellers are designed to “float” up and down between the diffusers.

What is Upthrust? When there is less pressure (low head) the impellers will “float” up and wear on the diffusers above. In an upthrust position there is a higher volume of water being pumped against lower pressure. As an example, this can occur in a shallow well application where the pump and motor have been oversized for the conditions of operation.

What is Down Thrust? When there is more pressure pushing down (high head) the impellers will “float” down and wear on the diffusers below. In a down thrust position there is a lower volume of water being pumped against higher pressure. As an example, this can occur in a deep well application where the pump and motor have been undersized for the conditions of operation.

What is the recommended operating range? When a pump is running within it’s recommended operating range the impellers will float between diffusers, thus reducing wear on the pump. This will occur when the pressure pushing down from above and the flow of water coming from below create a balance. The balance of pressure and flow when running in the pumps designed sweet spot will limit wear and, therefore, extend the life of your pump.

So, in conclusion, try to avoid upthrust and down thrust when possible. Please do not hesitate to contact us if you need help sizing a submersible pump for your system.

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