1/2" 9D-M3 Backflow preventer replacement

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Old 02-27-14, 09:12 AM
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1/2" 9D-M3 Backflow preventer replacement

I am going to be replacing my 9D also, and I have a question about the procedure.

Is there anything I need to do to avoid getting air into the system - once I isolate the 9D, remove and replace do I just open the valves and let the air into the heating system assuming it will get removed by the air scoop above the expansion tank?

Thanks
 
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Old 02-27-14, 11:15 AM
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Hello..

Yes you are correct. the small amount of air will be removed by the air scoop. As long as the AAV's are working.

Also the less air if you have valves on each side to isolate the 9d completely..
 
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Old 02-27-14, 03:55 PM
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I had a small issue with mine being air locked after change as it was between the Pressure reducing valve and a shut off. The PRV did not allow the air through and the 9d leaked. A few quick open and closes of the water feed solved that
 
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Old 02-27-14, 04:08 PM
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I have a shut off (feed side), bf preventer, pressure reducer, shut off (system side) - so I may also have get an air lock issue - did you open and close the feed side shut off, or cycle the pressure reducing valve?
Thks
 
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Old 02-27-14, 04:45 PM
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You could also pressurize it and slightly crack open the union connetions to vent any trapped air.
 
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Old 02-27-14, 04:52 PM
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Water/air should not get past PRV. I was air locked between the PRV and 9D I cycled the PRV, but you could also leave the union loose a smidge and turn on the feed and let the water take the place of the air. That way no new water in the boiler
 
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Old 02-27-14, 05:04 PM
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Thanks for the help, I'll wait until our temps go above zero in case I screw things up and am left with no heat, then give it a go
 
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Old 02-27-14, 05:36 PM
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really a no brainer if you have unions, it takes about 5 minutes to change it.
Here is the thread when I did mine.
http://www.doityourself.com/forum/bo...l-leaking.html
 
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