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Old 04-18-2019, 11:13 AM   #1
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Plumber ???

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Ok...confused here.

http://www.airforums.com/forums/f163...ml#post1708060

So we have a new brass vac breaker yet still need a check valve?

I thought the vac breaker prevents back flow? What am a missing?

https://www.bing.com/search?pc=DOWI&...vacuum+breaker

https://www.bing.com/search?pc=DOWI&...of+check+valve
Any plumbers our there that can explain the different function of each or why both are required as it appears the functions are the same.

Looks like the AS OEM part is a combo back flow preventer and check valve. Those needing to replace the failed OEM with a brass unit it seems now have two parts.


Thx, Bob
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Old 04-18-2019, 12:00 PM   #2
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A standard vacuum breaker prevents water from being sucked backward through the vacuum breaker. It relieves this suction by admitting air to the inlet side of the vacuum breaker. It does not prevent water under pressure from the outlet side from flowing backwards through the vacuum breaker.

A check valve stops water from flowing backwards under any circumstances. It does not relive suction by admitting air like a vacuum breaker does.

The reason there are often a vacuum breaker and a check valve installed in series is for code requirements and redundancy.

Buildings sometimes have a double vacuum breaker and backflow prevention valve for similar code required reasons. These are usually really big valves.
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Old 04-18-2019, 01:10 PM   #3
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Like Rich said, redundancy in case of a very unlikely situation. For example, you have your black tank flush hooked up and a pipe in the campground potable water source bursts and water is able to flow backward into the system. If your check valve is working it stops any backflow. If your checkvalve is broken and allows back flow, the vacuum break lets air into the line and stops the syphon, and vice-versa.
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Old 04-18-2019, 02:03 PM   #4
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The subtle thing with check valves is they are usually ok stopping pressurized water flow, but donít always seal tight against air or vacuum.

And the rubber seals donít always last Ďforeverí. Iíve had cheap backflow valves on garden hose connectors fail and leak all over the place. It also does not help when they use a setscrew that breaks off by design to keep them on. When that happens, you have to replace the hose valve as well.
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Old 04-18-2019, 02:29 PM   #5
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... It also does not help when they use a setscrew that breaks off by design to keep them on. When that happens, you have to replace the hose valve as well.
Which is why I remove those setscrews and throw them away prior to installation.
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Old 04-18-2019, 02:49 PM   #6
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Thanks!

Perfect everyone, thanks.


Ex of the city as a housing rehab manager...Code and redundancy I understand.



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