Rotary Motors
Rotary motors turn the impeller in the rotary pump, it's simple yet there are several options.. Motors will vary slightly depending on weather they sit internally or externally to the machine, and the size with larger motors needs for high output accounts or larger machine such as four group machines. The connection the the pump also varies, with common options being clamp ring, two-bolt or three-bolt connections.
Generally, it is better for a motor to sit externally to the machine as this reduced noise at the counter for the barista and customer, as well as reducing vibration within the machine and allowing for pump pressure to be easily adjustable.
If the motor sits internally, water-cooled motors are a good option as this allows the inlet water to cool and motor and pre-warm the water to increase machine stability.