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I am using this setup to maintain Mash temp.

Pump 1 circulates hot water from the HLT through one side of the Counter Flow Chiller.
Pump 2 circulates wort from the Mash Tun through the other side of the Counter Flow Chiller.

I was able to maintain the Mash temp within 2 degrees of target over a 90 minute mash.

This is completely manual setup. I found it best to keep the HLT water temp at about 180 degrees. Start Pump 1 shortly before you need to start Pump 2. This allows the Counter Flow to heat up prior to pumping the wort through it.