[Greenbuilding] Special Valve

[Speireag Alden]

Hallo, all.

     Sometime over the winter, or in early spring, I'll be installing 
a small solar panel over my well head, which will run a small, 
low-flow pump in parallel to my regular well pump (and higher up in 
the well case).  I want the low flow pump to top off the house 
pressure, and then, as it keeps running, drive the remaining water to 
the pond.

     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.

     I called my local building supply, and they're not familiar with 
such a valve.

     Can anyone here think how to do this?  (Preferably without power 
consumption.)

-Speireag.

-- 
Leaves starting to turn
Anticipation shivers
Me as winter comes

-Speireag.