A rotary pump is a mechanical device driven by an electrical motor. It also contains quite a few complex components to achieve the correct and constant pressure to the group heads
. To achieve this, the motor spins a series of vain's that are offset inside a central chamber. As the vain's rotate against the wall of the chamber, incoming water is compressed and thus pressurized before exiting the pump chamber. The pressure can be adjusted (within limits) by means of an adjustment screw mounted on the side of the pump body.
For: Stable pressure with quieter operation, longer lifespan.
Against: Physical size where space is tight.