How to distinguish between single-stage centrifugal pump and multi-stage clean water centrifugal pump?

Single-stage clean water centrifugal pump is no matter how many impeller, as long as the water is in the same pipe access. Multi-level centrifugal pump is not the same water, each of the impeller out of water are not the same, the water is the first post-pole water, each one for the impeller, is gradually pressurized. Single-stage clean water centrifugal pump is an impeller and multiple impellers in a cavity. Multistage water centrifugal pump is a few chambers outside the pump can be divided.