I have a 13 Gallon tank in my compressor. I can get the pressure up to over 100 PSI, but when I allow air to flow into individual sprinkler zones, the pressure at my manifold reads only about 10-15 PSI, although the guages on the compresser read over 80PSI during the whole operation. My guess is that the flow of air is limited by the diameter of the hose fittings, or maybe I don't know how to set the regulators on the compressor. How can I get more volume of air to flow? My compressor has 2 outlets. Can I attach 2 hoses to the compressor and have them attach to the sprinkler manifold using 2 couplers with a "Y" connecter? I know the professionals use a larger hose and I believe go through a garden hose size opening.
There are probably two things at work here, the limitations of the diameter of your hose and fittings, and the volume capacity of your compressor.
You are attempting to move air through 1/2" or larger sprinkler pipes, probably many feet, and possibly many branches; you need to deliver the air into the system faster than it exits through sprinkler heads, etc., in order to build up pressure (although I think for purging a system, volume is probably more important than pressure).
Your compressor has a rating in CFM @ PSI -- this indicates how many cubic feet per minute can be delivered at a specific pressure; one 13 Gallon unit I picked at random on Google supports 3.8CFM @ 90 PSI, which is not a lot to pressurize an open system with many feet of tubing.
If your runs are not too long, you may be able to get by using two hoses in parallel to get more volume into the sprinkler system (assuming they aren't both fed by a common small fitting somewhere; it's likely that the two fittings are intended for convenience rather than parallel operation), otherwise, your best solution is probably to rent a big compressor to do the job.
You probably don't want 100PSI in your pipes, and from the sounds of things, you don't. What I do on my sprinkler system is set my compressor regulator to 50psi (the same as my water pressure). I then apply the air pressure to the piping. Then I open and close each valve several times, allowing the air lines to come back up to the full 50psi before opening the valve.