Blow air through PVB? - Page 3 - LawnSite.com™

Mjtrole · #21 07-31-2011, 11:19 AM

Quote:

Originally Posted by DanaMac

The best way is to blow out from a connection down stream of any backflow preventer. But we blew out through the PVB or RP on probably 700 of the 900 we did last year. Do it right, and you won't have a problem. it's not my preferred method, but I won't be able to convince the other 700 to change their set up when it's been done this way for years. And no way I would have time to change them all during the blow out season.

if we are doing freeze damage repairs in the spring for a customer, we add a tee in there for blowing out.

Same as here, its a waste of time explaining this to anybody we always would get "that's the way its been for 10 years" so we just dropped the matter a together.

It's rather comical, we have some cities that will not pass a backflow unless there is a 3/4" threaded drain cap that is used to drain/winterize from and others that will not pass a backflow if there is any threaded connection before the backflow.

Wet_Boots · #22 07-31-2011, 11:43 AM

I can see worries over an "opportunity to contaminate" that a garden hose connection upstream of a backflow preventer presents, but I would worry far more over losing the low-point drainage that those blowout valves provide, for a system supply that exits the house foundation above grade.

AI Inc · #23 08-01-2011, 06:34 AM

We plumb them all before the pvb. If thye system is being inspected , we will install a plug there and then put in a boiler drain come blowout.

DanaMac · #24 08-01-2011, 10:01 AM

if done properly, and if you set your compressor PSI at a manageable level, there should be no problems. If the hot air is going to warp or damage a bonnet/poppet/check valve, then it would also warp or damage a zone valve, pipe, or heads. It's all in how you do it, no different than an install.

Now if it's a massive system, with dozens or hundreds of zones, and the compressor is going to be pushing for an hour, then sure they may be more heat than you would like. On a system like that, if there is no blow out port, I will find a manifold or mainline drain to hook to.

Wet_Boots · #25 08-01-2011, 10:14 AM

I wonder, who here has seen a melted backflow from compressor heat?

DanaMac · #26 08-01-2011, 10:24 AM

I've seen damaged internal components, but whose to say that they were not already like that before I blew out the system. I've seen some weird things with PVBs/RPs where components are damaged but the unit does not leak at all.