SPRINKLER TALK FORUM - You Got Questions, We've Got Answers

I am trying to blowout a large irrigation system. The mainline is 2" thinwall SCH40, 1" SCH40 feeder lines, and then black poly running out to the sprinkler heads. There are 11 zones with the last zone valve being at least 1000 ft from the back-flow preventer. First I tried my portable compressor (under 5 cfm) @ 50 psi. I know you laughing now...so I don't have to explain how that went. Then I went and rented a 20cfm compressor from Sunbelt Rentals. That went exactly like the first attempt. Then I decided to use the commercial compressor (it was at a factory) inside the business and run 300 ft of 3/8" airline from that at 50psi. STILL NOTHING. So I hooked the water back up to be sure I didn't have a break somewhere and the water has no problem pushing the heads up.

Am I just WAY short in cfm on my compressor? I would have thought that an industrial compressor from the factory would have made short work of it. Instead, I spent 4 hours and didn't get anywhere.

I was connected to the system just past the backflow preventer. No air leaks in the line or connection.

Opinions welcome, smarta** remarks...not so much.

Should I just increase the pressure in order to compensate or do you think that I will be flirting with problems? My only alternative is to rent a pull behind compressor or bring in someone else who has one.

I was thinking of putting a pressure regulator/gauge at the end of the 300 feet of 3/8 line and slowly turning up the Pressure at the supply end until i have 50 psi at the end of the length of hose. I thought maybe i could compensate for the pressure loss that way. I'm not trying to beat a dead horse, only seeing if i have a solution that doesn't require additional equipment/tools. The hose is rated at 300psi so i doubt i would even be remotely close to needing that much to compensate.

Thanks for your responses....they have been very helpful.