"Steve Kraus" wrote in message
k.net...
What is the normal working pressure? Just city water main pressure?
What's that, about 50 psi or something? Probably no need to exceed
working
pressure and a bad idea I would think, if you are leaving the heads in
place. The other idea, if there is water in the section you need to blow
out, is just to ease on the pressure gradually and watch the water flow
out
the drain at the other end using just enough pressure to do this. If it's
a fairly flat run between the two point then only a few lbs would probably
do it. If you have verticals connecting floors then a bit more.

Is there a way you could push 50/50 antifreeze/water solution through the
affected area so it could just sit there?

This is just reasonable speculation. Maybe someone more knowledgeable
will
know for sure.

There are a couple websites which explain this process. Try Rainbirds site,
or do searches.
Don't confuse pressure with volume. You need a high volume compressor,
which most homeowners don't have. You can rent a high volume compressor, or
just pay someone who does this service.
We're talking 25+ CFM airflow at a relatively low pressure- 20 psi or
lower.
Do not equate water pressure with air pressure. If you go with 50 psi, you
may end up blowing your sprinkler heads into orbit, and or melting your
sprinkler components. Compressed air gets hot.
You can't use a typical 120v air compressor (6 - 10 cfm) and make up for
the low airflow by increasing the pressure.