I would like to have an explanation of what a balancing valve does in a hot water heating system and when manual valves are used and when powered valves are used. Any and all information about these hot water heating system valves would be appreciated.

I hope the link below will help you, Thanks.

John

How to balance your central heating system. How to get your radiators all to the same temperature

Manual valves are used for isolation and service so the entire system doesn't have to be drained to replace a pump.

Powered valves in a consumer system are generally used to turn on zones. In a commercial system they may be proportional. e.g. You want a particular loop temp.