Leak from PVB on Backflow Preventer


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Old 05-08-20, 11:00 AM
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Leak from PVB on Backflow Preventer

Have a slow leak on my backflow preventer.
I replaced the bonnet and added a new o-ring, but I still have some slight seepage coming through.

Any idea what could be causing this? Would plumber's grease or a silicone sealant on the o-ring and threads of the bonnet help?
 
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Old 05-08-20, 10:26 PM
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Doubtful grease would help.
Not sure I'd want any type of sealant like that inside the valve.

Post the model number off its tag.
 
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Old 05-08-20, 11:33 PM
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It's a Watts 800M4QT 3/4"
 
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Old 05-09-20, 09:07 AM
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I was looking at the construction. The valve is bronze and the bonnet is plastic or bakelite. Not likely there's a problem with the casting which leaves the o ring or the actual bonnet as the problem.

You could try some vaseline or plumbers grease on the o ring.
Your next step would be to try another o ring and then replace the cap if the leak is still there.
 
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Old 05-09-20, 09:17 AM
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A few wraps of teflon tape on the threads would also not hurt but it is the Oring that should do the sealing.
I am with PJmax on greasing the Oring. This should help prevent it from deforming when tightening/compressing..

 
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Old 05-09-20, 09:56 AM
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Any chance it was left out and froze? I have seen several of those, that plastic cage holds the valve asm and the plastic can crack. Take it out and inspect, they are cheap to replace!
 
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Old 05-09-20, 09:58 AM
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There is a plastic assembly inside but the problem is the bonnet cover is leaking.
Possibly the plastic bonnet is distorted from freezing.

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Old 05-09-20, 04:45 PM
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I was thinking about the tape

its not frozen because itís a brand new bonnet and o-ring

ill try some grease on the o-ring as well
 
 

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