Problem blowing out sprinkler

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 " 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?
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Not sure, but I know in general the problem is that your pressure can be high enough to damage system, while cfm is too low. I'm impressed that you got it to work last year, as it may with a small system, but usually wiser to bring in a pro. Irrigation co charged me $60 last year, seemed reasonable. Got new seed in this year, so I'm still using it.
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You're moving too little air. 50 PSI is right, but you need probably double or triple the volume you're getting at the pressure tap. http://www.sprinklerwarehouse.com/LawnCare/Winterblow.asp
R
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125 feet of small diameter tubing will not allow enough air to move through the system. You will need much larger diameter, or preferably shorter length. Moving the compressor close to the sprinkler piping would certainly help.
wrote:

You're moving too little air. 50 PSI is right, but you need probably double or triple the volume you're getting at the pressure tap. http://www.sprinklerwarehouse.com/LawnCare/Winterblow.asp
R
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Is there a way you can blow it out after the breaker? I also have a vacuum breaker and I had a similiar problem. Sometimes if I lowered the air output a little , the breaker would close, then I would gradually increase the PSI output again. What I eventually did is put a drain valve after the breaker, with a seperate shut-off as to not backfeed into the breaker.
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Computer Prog wrote:

What you suspect is the problem is indeed the problem. You need a lot of volume of air and 25 gallon 5 hp (it isn't really 5 hp) won't do it. People who blow out irrigation lines here all use the large gasoline powered pull behind a vehicle type of compressor.
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I think that the issue is with the vacuum breaker. You're losing pressure there and that is why the heads don't pop up. If you could bypass the breaker, I think you would be fine. Though, I am not sure how you can do that without seeing the setup. Is there a shutoff valve between the breaker and the drain plug? Also, do you know if you have an automatic drain at the end of each zone? I used to use a 12 gallon compressor years back on a similar sized sprinkler system at my old house and it was always sufficient to blow out the lines. Granted, I had to let the tank fill 1/2 dozen times per zone, but it did the job. It wouldn't work with the system at my new house due to more zones and longer lines. Now I'm using a 35 gallon tank. FWIW, I add some windshield washer fluid to each zone to mix with any remaining water in the lines when I'm through for added protection. I figure that's good to -20F. With a compressor, the key is tank size. Bigger is better when it comes to the size of the air tank. My 2 cents on your compressor setup: Always use the biggest diameter hose you can and keep the hose short. The longer the hose, the more pressure loss at the end of the line. I think that your 25 gallon tank can do the job.
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I have a similar compressor and have also seen problems like this sometimes when blowing out my system. And I've also seen problems where water mysteriously sprays out of the backflow preventer during Spring start up.
I'm not an expert on what's inside the backflow preventers, but essentially it relies on a moving plastic object being pushed by water to close a passage. I think the problem is that air has a lot less mass, and the widget may not move as easy with air as it would getting hit with water. So, I think it must get stuck mid-way, with the air continuing to go around it. This is probably less of an issue with a compressor that can deliver more CFM. The ones we have are marginal, though they will do the job.
I'd try the following:
1 - Go back to running water through it again. This should get the valve operating properly again. Then you can try air again.
2 - Rap the backflow valve with a hammer to try to free it up without air on it, then apply air and rap again if still misbehaving.
3 - Take the top cover off the backflow valve. On mine, the thing comes apart easily with just 3 screws and you can pull out part of the mechanism. Every time I've done that and put it back together, it's gone back to behaving again.
Also, the total size of the system is usually not a factor for a home system. They are set up on zones. You only need to have the capacity to do one zone at a time. Whether there are 3 zones or 12 doesn't matter. What does matter primarily is the nozzle size and how many heads per zone.
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Computer Prog wrote:

Hi, Tour compressor is too small. I blow my 7 zone system myself and compressor is belt driven Campbell Houser Extreme duty one. I can barely do the job with this one.
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Good heavens.
I blow my 9 zone system with a piddly 3/4HP CH compressor with a 3 gal tank without any trouble whatsoever.
Yes, it can't blow each of the lines continuously, but that's not the issue here - the air tank will recharge, it just takes a bit of patience.
Remember: there's water in the lines. If you stick 30PSI or more of air pressure behind the water, you can damn betcha that water is going to blow the popups up at least until the first one in the series blows air.
[In my case, the air flow from the _tank_ is enough to have all of the popups in a 13 popup string blow air. The popups that are closer to the air tank fall after blowing air for a while, but the later ones will still pop.]
If that's not working, you have either a massive air leak somewhere (which you should hear), or the valve/vacuum breaker/whatever aren't working the way you think they are, and the air isn't going anywhere.
Yes, 150' of airline seems kinda much, but, that should still be far more than enough to get more than a faint gurgle.
I think something's stuck somewhere in the OP's situation.
Perhaps the zone valves are being stubborn. I have some where the manual lever doesn't work.
My system has the water supply "fork" to the underground sprinklers and a hose bib just beyond the feed shutoff in the house. I turn off the shutoff, connect the air compressor to the hose bib, open the hosebib valve, and in turn manually switch each of the zone valves.
--
Chris Lewis, Una confibula non set est
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This is what my system looks like:
http://www.i2.i-2000.com/~rbartick/wilson.jpg
The lower right side of the picture is the water main from the house. The left side is the water going to the electronic valves. I was connected my air line to the removable drain cap seen at the bottom of the PVC on the right side of the picture. This cap is before the breaker. I also tried to connect my air line to the small test port on the upper right side of the picture right below the Wilson breaker. I didn't try to connect air to the small test port after the breaker on the left side of the picture because I was worried that air might flow back towards the valve in the wrong direction and possibly damage it.
I do not have auto drain valves and there are no other ports I can connect to. I definitely got the heads to pop last year using the drain plug but I am not sure what I did. I may have disconnected the 50-ft copper coil that sits on my compressor output. I am going to try to move the compressor right near the sprinkler valve and run a short line from the compressor to the sprinkler.
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Moving the compressor should help. If you really want to see the heads "pop", run the water first so the compressor can develop some pressure in the system. If the water is already gone, maybe your compressor is inadequate to develope enough volume with high leakage at the heads.
Bob
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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.
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Computer Prog wrote:

If you can some how put a hose bib after the shut-off valve after the breaker, that should solve the problem.
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I moved the compressor very close to breaker and ran a short hose to the pressure port. This allowed me to blow out my sprinklers properly. The breaker stops "gurgling" after I give it enough airflow to "open it", at which point the air goes to the heads and they pop up. That point seems to be an indicated 65-70 PSI on my compressor output gauge. Once the heads pop I can immediately reduce the air pressure and the breaker will remain open with the heads remaining up. I reduced it to an indicated 50 PSI after the heads popped up. The heads will remain up even if I dial the pressure down to an indicated 25 PSI.
My compressor was not able to keep up with the airflow at 50 PSI so the pressure dropped slowly as I blew out the lines. I had to cut the airflow to allow the compressor to catch up a handful of times.
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