What type of multi-stage pump has three impellers?

The correct answer indicates that the multi-stage pump in question has a configuration that specifically includes three impellers. In the context of multi-stage pumps, a three-stage pump is designed to have three distinct impellers, each contributing to the overall increase in pressure and flow rate of the fluid being moved.

Multi-stage pumps are utilized to achieve higher pressures than what a single impeller can provide. Each impeller in a three-stage pump works sequentially, increasing the pressure of the liquid progressively as it moves through each stage. This design is particularly useful in applications where significant elevation changes or higher pressure is necessary, such as water distribution systems.

Single-stage pumps have only one impeller and therefore cannot achieve the same pressure increases that multi-stage pumps can. Two-stage pumps would only have two impellers, and a quad-stage pump would have four, thus being inconsistent with the requirement of having exactly three impellers like in the question. This precise arrangement of three impellers is what designates it specifically as a three-stage pump.