Want to add speed control to a single speed circulator pump

[Smooky]

So, how do you control speed on a recirculating pump? Voltage control (ie. variac), or pulse-width-modulation or current limiting. Is this even possible? Isn't it a simple ac motor? I have Grundfos pumps, some 3 speed others 1 speed.

Instead of changing the speed you could add a valve to reduce the flow. What problem are you having that you need to do that?

 

[Dana]

For pumps running a very high duty cycle it can be worth swapping in a "smart" programmable pump with an ECM drive DC motor, using a small fraction of the power used by an AC motor with it's flow restricted by ball valves. (eg: Grundfos Alpha or Taco Viridian or B & G ecocirc, etc.) They're not cheap, but "worth it" in high-priced electricity markets for pumps that run almost constantly.