I put my blowout port after the breaker valve and I have yet to damage
the breaker valve in 6 years by blowing out the lines. Keep your hose
from the compressor to the blowout port as short as possible and blow
out one zone at a time. The longer the hose from the compressor, the
more pressure that is lost at the end of the hose. I agree with a
number of the other posters that have stated that adding a little water
to the lines and then hooking up the compressor will get the heads up
assuming you have no leaks in your system. Once there is little to no
water in the lines, then air alone from your compressor will likely not
raise the heads. If that's the case, then you're done anyway. I've
been winterizing my sprinkler system and a few of my neighbors now for
the past 15 years and all of our systems have survived the winters.
I've gone from a 12 gallon tank to a 35 gallon tank and both have
worked fine. So should your compressor.