[Greenbuilding] Special Valve

[Doug Horgan]

Speireag,

   "In order to do this, I need a valve which will let water go to 
the pond if pressure exceeds a given limit, but otherwise won't let 
water flow in that direction."

In our area (Washington DC) we sometimes use a supplemental pressure relief valve, in conjunction with a pressure reducing device at the main water inlet to the house. The conventional reducing device on the main prevents high water pressure in the house while water is being used regularly, but I've been told pressure eventually equalizes if you don't continually run water inside the house and thereby drop the pressure on the house side. I've seen pressure well north of 100PSI and plumbers seem to get very nervous when the see the gauge up in that territory. Anyway, the easiest relief valve to install is a toilet ballcock that also has a valve that pops at _x_ psi and lets the water run until the pressure comes back down to _y_.
I found a page on thermal expansion control that also mentions a few other kinds of devices that perform a similar function and may be more suitable for your situation:

http://www.coweta.ga.us/Resources/What%20is%20Thermal%20Expansion.pdf

best of luck,

Doug
Doug Horgan
Team Leader--Customer Service
BOWA Builders, Inc.
7900 Westpark Drive, Suite A10, McLean, VA  22102


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