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Posted by Heatpro on January 22, 2006 at 11:42:06:
In Reply to: Re: a few minor problems after our repiping posted by Dave on January 22, 2006 at 11:18:17:
It would make sense that there will be gravity flow through the standing vertical large pipes through the middle of the pipe and down the outside of the same pipes. That does happen with large pipe.
The same can happen in pipes that are as small as 3/4-inch. The reason for the flow checks inside or after the circulators is to stop that gravity flow and to stop other pumps from pumping backwards through other loops when one of the pumps is on and the others not; their purpose is to prevent flow at the point they are installed. If they are allowing gravity flow, they are either manually opened, stuck open, installed wrong, the wrong kind, or simply not doing the job due to amazingly high differentials in gravity from supply to return, (which shouldn't be happening with radiant floor, nor fan coils, as they have heads over 2 psig by themselves without piping resistances added.)
http://64.226.150.132/hydronic/multcirc/multcirc.htm