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Using a 125PSI compressor for sprinkler blowout??

Peter78's Avatar

Join Date: Aug 2008
Posts: 6

10-11-08, 07:38 AM   #1 (permalink)  
Using a 125PSI compressor for sprinkler blowout??


I have a small 5 Gal, 125 PSI compressor and I wish to use it to clear out the sprinkler system.

However, some information I have read on sprinklers recommend using a steady 30 CFM at a pressure of only 30 PSI. The high pressure could fracture the pipe and high speed could cause excessive heat and wear. If I fill the tank to 30 PSI, my tank is too small and I bleed all the air in less than a minute.

I thought about adding a 11 Gal portable tank to the system.
Is it possible to connect my 125 PSI compressor with 5 gal tank to an 11 gal tank and then put the regulator on the end? That would give me a 16 gal tank, allowing me to run 30PSI about 3 times longer.

Would this work?

What additional hardware would I need?

Thanks, I appreciate your advice.

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nap's Avatar
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Join Date: May 2006
Posts: 4,163

10-11-08, 11:02 AM   #2 (permalink)  
Your biggest problem is providing the 30 cfm. That is a lot of air. If you do not have enough flow (CFM) it will not push the water from the lines. It will be able to flow past the water and leave the water in the lines.

the pressure you are releasing is not as relevent as the pressure within the sprinkler lines. If you do not have enough flow, you could run 500 psi into the lines and still not develope any pressure in the sprinkler lines.

The developed pressure in the lines is what needs to be limited to 30 psi, not what you are releasing into the lines. If you have enough flow, then yes, you would limit your release pressure to the 30 psi but if that does not maintain 30 psi in the sprinkler lines, you are not getting the job done.

Peter78's Avatar

Join Date: Aug 2008
Posts: 6

10-12-08, 07:19 AM   #3 (permalink)  
Thank you for your response.

My compressor cannot maintain that flow rate so I was hoping to use the 11 and 5 gallon tanks together as a buffer so that I can maintain 30 CFM for at least 30 seconds.

Last year I cleared the sprinklers by giving short puffs of 125 PSI out of the 5 gallon tank only. I wasn't too happy with that as I think the high pressure might damage some of the components.

This year I hope to use lower pressure out of a the combined tanks and maintain it a little longer.

chengny's Avatar

Join Date: Aug 2007
Posts: 28

10-17-08, 03:24 AM   #4 (permalink)  
Just a couple of thoughts on winterizing your irrigation system:

1. Properly blowing lines clear of water is more dependent on the volume of the compressed air than the pressure. And, the flow rate/volume is a function of several things, the number of heads on the zone having the most impact. To illustrate my point I will exaggerate - imagine that you have 100 heads on one zone. Each nozzle will share the task of allowing the pressure in the lines to equalize with atmospheric. So, assuming that you are supplying the blowing medium (compressed air) via a 3/8" hose, the flow through an individual nozzle/head would be negligible. Taking it to the other extreme; say you, for some reason, had a zone with only one pop-up on it. When you admitted the air to the system the entire volume that passed through the air hose would be directed to that one little orifice - effecting a very thorough blow-out.

If you follwed that line of reasoning, then you can see the importance of the size of the air hose and the fittings that you use to hook up with. No matter what the pressure or capacity rating of the compressor - if you try to force it's output through a reduced diameter you will lose the blowing effect to some extent.

I realize that at this point you have what you have as far as heads on a particular zone. The only thing you can control is the volume of air.

At this point I have to interject; whoever told you that 30 psi was the maximum allowable pressure that you could apply to your irrigation system is shooting it out their butt. Think about it; most household potable water systems run anywhere from 60 - 90 psi. This is the pressure that the piping sees all summer long - when the solenoid to a zone opens. A properly plumbed sprinkler system - using black poly pipe and double clamps could easily withstand 200 psi - as will any name brand (Hunter, Toro, even that Home Depot junk) head

Anyway - if you want to do a good, quick job of blowing your lines, go to the local equipment rental store and get a nice big rotary compressor. They have them now that can fit right in the back of your van or pick-up. It will come with about 100 feet of 1 inch air hose which will have a quick connect fitting on the end. The guy at the counter will lend you (or sell you for about 3 bucks) a similar fitting with pipe threads to connect to the one on the hose. Go to the hardware store and ask the man for a "hose to pipe adaptor" (again maybe $3)of the proper size to thread on to the quick connect. Get male threads on the garden hose side. Also, while you are there, if you don't have one laying around, pick up a washing machine water hook up hose (the kind with double female connections). This will go from the garden hose/pipe adaptor and the other end will screw right on to your blow out connection that is permanantly piped into the irrigation system.

Start the compressor and run through all of your zones 3 or 4 times for 5 mins or so each. You will have already done all the hard work, so just sit back watch all the pretty mist and have a cold one.

When you are done - and this is a real good tip - leave the blow out valve wide open. If, during the course of the long winter, the isolation valve (you know, the one you shut before you began blowing the lines) should ever leak and the blow out valve is shut.... It won't take long before that tiny leak will fill up the pipe between the nice warm cellar and the water will get out into your control box. Thats where the solenoids live and they do not tolerate ice like your lines can.

It is seems to me that a drip in the cellar is a small price to pay to keep that cont. box dry! BTW - that control box (and the solenoid valves that it contains) is the real reason that we blow lines. Black poly pipe and the heads can take the expansion caused by ice formation. The money is in the box!

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