Quote:
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Originally Posted by Doctor Evil
...You put a check valve on each CH zone to prevent back circulation. Each pump can have its speed set to the needs of the zone. There will be no parasitic circulation if each zone has its own flow and return tapping off the store.
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Please explain what a check valve does - any weblinks with nice pictures?
I did a search and found lots of people trying to sell them, but I've still no idea why I would want one..