Backflow preventer - is it working

Hen

Hello.  How can I tell if my residential backflow preventer is good or not?  The preventer is over 20 years old.  Should the side port (has a short drain-like open outlet pipe) leak water when feeding the boiler?  The boiler water feed valve, does it belong above or below the preventer?  If I have two 'feed valves', one is above and one below the preventer, will that affect the function of the preventer?  One valve was leaking years ago and a second was added on the opposite preventer side without removing the original leaky one.  Thank you.

Dave in QCA

Test it

These devices should be tested by a certified tester who has the appropriate test gauges and the knowledge necessary to conduct the test.

Brad White

Quick Test

I presume you are using a Watts 9D or similar residential grade BFP? The commercial ones (e.g. Watts 900 Series) have shraeder valves and/or petcocks for test gauges. These are typically for commercial work and are what Dave is perhaps speaking about.



The simple test for a 9D type is to open a large upstream branch valve (I would detail this going-in. If you actually have one, awesome). Ball valves are best.



By opening the valve suddenly you will immediately drop the pressure in the incoming line, possibly to a point below your heating system side. (Which is the idea, what you are protecting against).



When suddenly opened, the BFP checks should snap back toward the potable side and you will have a drip out of the center vent. 



I make the analogy that a BFP is like a building vestibule with two sets of doors in series which swing only in one direction, into the building. When both doors close suddenly, a trap door in the floor opens. Escape is impossible, or at least, very very difficult.



But you know what? If in doubt or if you are thinking of cutting in a test valve, buy a new one. If still made in the same model, it should go in easily.