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New Member


Tuesday, June 25th 2013, 3:41pm

Leaking PVB

I have a Watts 800M4FR pressure vacuum breaker. When I turned it on this year it started leaking from the top, apparently between the vent float and the bonnet. Information I found online suggested that I replace the faulty parts, so I did. In fact, I bought the full replacement kit and replaced every part in it, but it still continued leaking between the NEW vent float and bonnet.

I rebuilt it two more times, even tried using the sealant paste that the parts come with between the vent float and bonnet, but it still leaks. Here's a video: Any ideas? Thanks.

This post has been edited 1 times, last edit by "mrfixit" (Jun 25th 2013, 9:54pm)


Supreme Member

Posts: 5,330

Location: Metro NYC


Tuesday, June 25th 2013, 5:17pm

Did you use all the replacement parts? Including the large O-ring? Is this still the original cover/bonnet?


New Member


Tuesday, June 25th 2013, 9:18pm

Did you use all the replacement parts? Including the large O-ring? Is this still the original cover/bonnet?
Yep, all of them. Large O-ring, bonnet and cover included.



Posts: 2,393

Location: USA


Tuesday, June 25th 2013, 10:16pm

I can't say I've seen one do what your video's showing after being repaired so I'm grasping at straws here.
Since you have the same issue even after installing new parts I'm thinking maybe the issue is elsewhere.
Has there been a drop in water pressure?
Do the sprinklers have full pressure?
I've seen ball valves break where it looks like they're open because the handle is inline with the pipe but the ball inside only partially opened.
Is there a pressure regulator on the system?
Is there another shut off valve that's not on all the way?
Maybe you bought faulty parts.

Maybe the thing froze and is irrepairable.
That's all I have.


New Member


Wednesday, June 26th 2013, 7:22pm

I'm not sure if the water pressure is right. It appears to be working properly, but I suppose it might be a bit low.

The problem I see with the partially-open valve theory is that the PVB still leaks even when the sprinklers are off. My physics background leads me to think that the pressure in the PVB would equal the pressure from the main water source if the water isn't flowing, as long as the valves are at least partially open. Does that sound right?

It's hard to imagine how freeze damage could cause a leak between brand new parts, so I think your faulty part theory sounds most likely to me. Maybe I'll try parts from another vendor and if that doesn't work, hire a pro.

Thanks for your input. It's helpful to know that I wasn't missing something obvious!


Supreme Member

Posts: 5,330

Location: Metro NYC


Thursday, June 27th 2013, 6:22am

The poppet for the 800M4FR has an internal "freeze bypass" that is supposed to let water pass through in in freeze conditions, and it could allow a continuous flow, once it first opens.

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