A VFD pump is a Variable Frequency Drive pump. It will convert 1 phase to 3 phase typically and some can also act as a soft start depending on the size of the pump.
Its used in places where three phase is not available where you need three phase power to power a three phase pump. Normally, you would size the pump seperately and use a VFD to supply the 3 phase from the single source, but this is a cost-effective alternative.
A VFD is an electrical system that controls an AC motor.
AC power is converted to DC power, then the DC supply altered, and then the DC is converted back to AC in order to control the speed of the motor. It doesnt convert 1phase to 3 phase.
The basics are shown here:
Since you posted this in the water distribution and treatment forum, I assume you were looking for some inkling about how a VFD can affect something like water flowrate or water pressure.
You can use them to slow a motor down and, if the motor is a pump driver, you will slow down the flowrate and reduce the differential head of the pump.
See "pump affinity" estimate equations to predict the results the decrease in rotational speed has on flow and head. The basic premises are,
The New_Flowrate = Old_Flowrate * New_Speed / Old_Speed
The New_Head = Old_Head * New_Speed^2 / Old_Speed^2
The New_Power = Old_Power * New_Speed^3 / Old_Speed^3
The relationships are valid where pump efficiency does not change and where system flowrate is also roughly proportional to the change in pump's differential head.
