Pump flow control with variac.

Hi all,
My brother just gave me a little Grundfos hot water circ pump. It has a bronze housing and pumps 17 GPM. It was used for hot water recirc. I want to use it if I can for my brewery build, but I think the flow rate is way more than I need. I would like to get it down to 4 GPM.

I have a 120Vac Variac transformer rated for 10A. Could I use this to slow the pump down? or would a ball valve on the output side be better?

Thanks, Dan.

If it's a magnetically coupled impeller then you can put a ball valve on the output side. Otherwise, the variac should work, but you might run into cooling problems if you run it too slow. depends on the motor type.