I have a small 4-zone system at my house. My property is about 100 feet
deep and 50 feet wide so the sprinkler system does not really cover much
land. The system has a Wilkins Model 420 Pressure Vacuum Breaker right
where the main water line comes out of the house before it goes to the four
zone valves. There is a drain plug in the main water line outside the
house that sits right below the Wilkins breaker. This drain plug is where
the pressure tap is connected to blow out the system.

I have a Sears 5.5 HP 25 gallon compressor that is rated at 8.6 CFM @ 40
PSI and 6.4 CFM @ 90 PSI. I have 50 feet of 3/8 copper tubing in a coil at
the output of my compressor going to a water filter and a quick release
fitting. I ran 75 feet of ½" rubber air hose (after the 50-ft copper coil)
out to the drain plug below my Wilkins breaker. I filled my compressor,
turned on one zone of my sprinkler and set turned my compressor regulator
to 50 PSI of output. I heard a lot of "gurgling" at the Wilkins breaker
but my sprinkler heads did not pop up. I raised the pressure a bit to 70
PSI but the sprinkler heads still did not pop up. I had a similar problem
last year but after a while of experimenting I got the sprinkler heads to
pop at 50 PSI and the "gurgling" went away. I am not sure how I got it to
work last year but I cannot get it to work again this year.

Does anyone have any ideas what the problem might be? Is it possible that
my compressor is not flowing enough CFM? Would it help if I pulled my
compressor out of garage and put it near the sprinkler drain plug and used
a much shorter rubber airline to hook up my pressure tap?