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I noticed a small leak of water when I turned on the sprinkler system this year. The leak seems to be coming from the top of the pressure vacuum breaker. Note this is not the exact picture of what I am dealing with, its the closest I could find online:

enter image description here

There are two screws at the top of this thing, should I be turning off the water and unscrewing these two screws...what could possibly be broken causing this leak? I really respect plumbers because boy do I hate leaks...

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up vote 5 down vote accepted

If you turn off the water to your sprinkler system you can them remove those two screws and take off the top of the pressure vacuum breaker. Inside you should see an O-ring that makes a nice seal. Check that the O-ring is in good condition and then also look for things like spider webs or wasp nests that are preventing a good seal.

If water is flowing into the sprinkler system the O-ring of the pressure vacuum breaker will prevent the water from leaking out. If water flows the reverse direction, the pressure vacuum breaker will open and prevent the water from going back into your house (and you drinking it). So if something is blocking the O-ring from making a good seal, then you could end up with a leak.

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The funny thing is I posted this at work and no one answered for a while...so I went home for the day. Popped it open and noticed the o ring rubber washer was worn out. Went to home depot and they didnt carry it, so I went to Ace / Aco (cant remember the name) and they had it. I replaced it and everything is fine now. I still will accept your answer because this is exactly what I did. – JonH Jun 15 '11 at 12:34
Ace has them. #39 O-Ring Bag. Part Number: 9D0035753B worked great for me. It was 59 cents. – user24921 Aug 31 '14 at 3:53

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