Pipe union and teflon tape

One of the four water pipe unions that I used to install two backflow preventers has a very minor leak.

Is the possible problem that I used teflon tape on the male part of the union threads?

That may be the problem. I hate teflon tape myself, I use old fashioned pipe dope. That said, the most likely problem is the unions don't perfectly line up. Some springs I have a hell of a time getting the backflow preventer on so that the two unions mate perfectly. End up with a small leak. Best thing I have found is to go back to square one and get them both in position and snug them down slowly like you were tightening lug nuts on a wheel. After they are both firm, then put the muscle to them.

Gary Swart said:

Some springs I have a hell of a time getting the backflow preventer on so that the two unions mate perfectly.

Click to expand...

Are you saying that you remove the backflow preventer during the winter??? That, actually, sounds like a good idea.

So do you stub out the two risers or just leave it open to the air?

I do remove the backflow preventer during the winter. I built an adapter for my air compressor that screws onto the 1/2 union left on the output side and blow the lines from that point. The other side drains via a stop and waste 5' underground where the tee from the main line is located. I store the unit inside during the winter so there is absolutely no chance that a little water left might freeze and break something. I put a plastic baggy over the exposed ends to keep any debris out. The adapter is just 1/2 of a 1" union, reducers, a 1/2" ball valve and an air hose fitting. My compressor is 7 hp with a 60 gallon tank. I use 2 tanks of air to blow each zone. It's slower than the pros who use the big industrial compressors and can blow the whole system at once, but I save $50 a year using equipment I already have. Reassemble of the backflow preventer in the spring takes just a few minutes.

Gary Swart said:

I do remove the backflow preventer during the winter. I built an adapter for my air compressor that screws onto the 1/2 union left on the output side and blow the lines from that point. The other side drains via a stop and waste 5' underground where the tee from the main line is located. I store the unit inside during the winter so there is absolutely no chance that a little water left might freeze and break something. I put a plastic baggy over the exposed ends to keep any debris out. The adapter is just 1/2 of a 1" union, reducers, a 1/2" ball valve and an air hose fitting. My compressor is 7 hp with a 60 gallon tank. I use 2 tanks of air to blow each zone. It's slower than the pros who use the big industrial compressors and can blow the whole system at once, but I save $50 a year using equipment I already have. Reassemble of the backflow preventer in the spring takes just a few minutes.

Click to expand...

Thanks, Gary, that answers a lot of questions.

Actually, what I did (without knowing it) mimics what you did and what I did and intend to do. The "only" added thing was the removal of the backflow preventer. I think that that's quite clever. Thanks.

Questions: How large is each zone of yours? What pressure do you use? Do I blow out zones with drip systems attached? Is there a difference in technique between blowing out a drip zone and a sprinkler zone?

My pressure is around 70 psi. The system was designed by a professional, and I really don't recall how many gmp's each zone uses, but I run 9 Rainbird impact sprinklers on each zone with no problem. The pipes start from the valve box with 1-1/4", drop to 1", then to 3/4" during the course of the runs. This is further reduced to 1/2" going into the sprinkler. I was told this has to do with friction loss. I can't answer your question for certain about the drip systems as I have never used one. I would assume however, you would have to open the ends to blow the water out. I'd suggest you speak to an irrigation installation company about that if you don't get an answer of this forum. I'd really hesitate to just apply air pressure to a drip line that was closed. Oh yeah, if I haven't already mention this, I have a 1" meter and it is piped to the backflow with 1" copper. There is about a 30' run from there to the valve box and that is with 1-1/2" just after leaving the backflow preventer.