What size air compressor?

Tim (NY) · Dec 19, 2013

My son is looking for a new air compressor. Besides the usual tires and basketballs, his main need is to blow out his lawn sprinkler lines in the fall. He wants to blow the water out at 40 psi without running out of air and waiting to re-pressure. I can't figure out how to convert this to cfm and tank size. Any ideas?

big jt · Dec 19, 2013

Shouldn't need a huge compressor. 20 gallon should do. Don't think the little pancake compressors would cut it but shouldn't need a bodyshop type either.

Is there a way to cap off all but the last sprinkler head in each run? If yes it won't take very much air at all, just enough to fill the lines.

I do something very similar with my crop sprayer at the end of season. Doesn't take very much air to blow out the lines but once the water is out a 5 horse 80 gallon can't keep up.

Nother suggestion, get a regulator, will allow to blow out lines at 40 and also have the reserve of a tank pressurized to 120 or 175 depending.

HTH
jt

Anonymous-0 · Dec 19, 2013

I tried blowing out my system with a 30 gallon 11.6 CFM compressor and as soon as one of the heads in a branch blew air instead of water the air pressure dropped and would not blow out the rest of the line.

Craig45 · Dec 19, 2013

Like JT says it doesn't take much air. I have an underground pipe from the house to my shop. Once the temp. Gets below freezing for a while I blow it out with air. I have a 30 gal tank set at 90 psi and it blows the water out of the line just fine. The line is 80 feet long.

jeffcat · Dec 19, 2013

When you blow out systems like this you need VOLUME not so much pressure. I just blew down my parents house water system up at the farm. This included the barn and shop. I had my little 3/4 hp Emglo AM 39 air compressor hooked to the shop that is every bit of two hundred yards of inch and quarter water line away from the pump house. Took most of twenty minutes till I was blowin just clean air but you will always have a tiny amount of water left behind. Just a little in the bottom will not do anything. Remember you want the water out of any low spots and you should have a removal cap at the end of the line. Never ever set your regulator above 40lbs. pressure. The bigger compressor I have is an Emglo 15k. This has a 1.5hp electric motor and a 6cfm "K" pump on it This unit really blows a lot of air through the lines! A lot of lawn care guys use 125cfm big time air compressors but they like the air spray visual effects and they want to get finished. One of my neighbors does lawn care and when they are all done he pours a bottle of RV antifreeze in to the system and blows that through. Never had a freeze up!

Craig45 · Dec 19, 2013

Second thought, I guess the pressure you use would depend on what kind of pipe you have. Mine is 3/4 galvanize .

waltdavies · Dec 19, 2013

Use your shop vac connect to the air side not the vacumn. Tape the hose to the water pipe turn on vac. You get enough volume to blow it clean in short order. We used this method to blow up huge rubber fuel tank used in an army portable fuel station.
Walt

Anonymous-0 · Dec 19, 2013

just like building a garage . decide how big you want than go a size bigger,

dpendzic · Dec 19, 2013

if you don"t want to re-pressurize then its simply a mater of CFM CfM= area of line times the velocity
my research shows 10 ft per second should push the water out--you will need to know the number of heads and there CFM--it would be advantageous if you have separate line feeds to only a percentage of all the heads and do one branch at a time.

Russ from MN · Dec 19, 2013

I use 2 small compressors, we have a 20 gallon pressure tank in our system and no more than 6 heads per zone. I run the pressure tank up to about 60 pounds and then open 1 zone valve. If I do this twice it is good enough.

Rick Kr · Dec 20, 2013

I used to install sprinklers years ago. We used an Ingersoll 185 CFM compressor to blow out the lines in the fall. You need volume and lots of it.

For your compressor, you have 7.5 (7.48) gallons per cubic foot.

When the first sprinkler is purged the air will want to take the path of least resistance versus pushing the water out of the rest of the heads.

It truly depends on how many heads per zone how much CFM you would need. Worst case if you cant push the water out of all of them you could hold your finger over the ones already purged to force the air to the other ones. This is where kids would come in handy. On a smaller compressor, you will start losing PSI quick. More gallons of air would help, even on a small compressor, adding another tank and letting it charge up would help.

Most of the bigger Rainbird residential heads max out around 8 gpm. Depending on how your system was designed, most people would have setup the heads around 4 gpm or so. This allows for a little adjustment either way. They run 30-40psi.

My info is 20 years ago since I worked on sprinklers.

Rick

Pops1532 · Dec 20, 2013

Rick's info sounds correct. The sprinkler contractors around here use the big tow behind compressors to blow out sprinkler lines. I'd guess 135-185 CFM.

What size air compressor?

Tim (NY)

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big jt

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Anonymous-0

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Craig45

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jeffcat

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Craig45

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waltdavies

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Anonymous-0

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Russ from MN

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