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.
How to increase the volume of air going into the lawn sprinkler zones to blow out water for the winter
compressorsprinkler-system
Related Solutions
Something like this should do ya just fine. You'd just have to attach it to the faucet you have and shut off the nearest valve. Should redirect the air down your sprinkler system and blow the water out of the sprinklers. You'll probably need to have a pretty hefty air compressor though, it's probably going to take quite a bit of pressure to get through your system if it's extensive.
My guess would be that there is something wrong with the backflow preventer.
Most likely, the air inlet valve is not sealing properly. When pressurized from the side marked "normal flow" (which is where your tap is), it should open the check valve, and also force the air inlet valve shut.
It's probably a rubber gasket, and might be worn out and need to be replaced, or maybe something is physically holding it open. Try pushing on it to see if you can get it to close all the way. Some silicon grease around the gasket will help it form a good seal and prolong the life of the gasket.
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Best Answer
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.