Is it OK to blow air through a Back Flow Preventer?

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  #1  
Old 11-08-16, 09:27 AM
R
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Is it OK to blow air through a Back Flow Preventer?

I want to blow out my sprinkler system for the winter. It has a 1" Watts 800M4 FR pressure vacuum breaker installed. The only way I can see to put air into the system is through the upstream or downstream test cocks on the PVB, or into a hose bib drain valve that is located upstream of the PVB (and downstream of the irrigation water supply cutoff valve).

Question: Will it damage the PVB to introduce compressed air into the hose bib drain valve? That way, air will flow completely through the PVB and into the sprinkler lines. I have tried putting air into the downstream testcock valve, but the air just escapes out of the PVB and I don't get pressure into the sprinkler line.

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Old 11-08-16, 05:27 PM
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Just a suggestion, but have you googled/youtubed winterizing sprinkler systems? I just found this video (by searching for "winterize sprinkler system pvb): https://www.youtube.com/watch?v=t3gaEXbvtIc

Hopefully it helps, otherwise try another one. (Sorry when I saw backflow I checked the thread, but I don't have much experience with pvbs or lawn sprinklers, dcva/rpzs and fire sprinklers on the other hand...)
 
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Old 11-10-16, 07:21 AM
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Thanks Evan. Good suggestion.

I actually had already watched all of the YouTube vids about winterizing an irrigation system. When it comes to blowing out the sprinkler lines, most of the videos connect compressed air downstream of the back-flow preventer, a few say "don't connect upstream of the back-flow because the air flow can damage it", but, a few clearly show connections upstream of the back-flow device through a hose bib drain like I have.

Since I can't connect downstream of the back-flow device, I thought I would post the question in this forum to see if anyone had more information on potential damage to the PVB caused by flowing compressed air through it.
 
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Old 11-14-16, 11:32 AM
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I don't know the answer to your question. Like you, I've seen warnings not to blow air through the PVB, but I don't know how dire the consequences really are.

When I installed my sprinkler system, I intentionally added a hose connection after the PVB and a shutoff at the PVB (actually part of the device), so I could isolate the PVB and blow out the rest of the system.

Could you add a hose connection there easily enough? If it's PVC, it may be able to be added pretty easily?
 
 

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