As long as the VFD will still run the motor at full speed, you can convert it to an electronic soft start. With some Drives you can use the two wires from the pressure transducer directly on a standard pressure switch. Other drives will have a place for two wires from a switch or pilot control and the transducer wires are just disconnected. You will have to read the wiring diagram for the particular Drive to determine which two connections to make to a pressure switch. Then if possible you want to program the Drive to ramp up within 2 to 3 seconds. Install a Cycle Stop Valve on the discharge of the pump and tee off to a small bladder tank with the pressure switch as per normal Cycle Stop Valve instructions. Adjusting the Cycle Stop Valve and pressure switch as per normal instructions will allow you to use from 5 GPM to 200 GPM and maintain 70 PSI. The pressure switch adjustment can be according to the size of tank installed. Normally a 60/80 pressure switch setting with about an 80 gallon tank will store 18 gallons for leaks and gives you almost 2 minutes of run time after all the sprinklers go off. Later on when the drive completely fails you can easily switch over to a standard across the line starter or another soft start. I find the old style Auto Transformer type soft start panels to be more reliable than electronic soft starters if you can find one.
