Air compressor for winterizing inground sprinklers

[trader4]

"The sprinkler company says that it takes between 10 and 25 CFM to properly blow out the sprinkler lines. I have a 4 gallon/125psi compressor but the specs don't include it's CFM rating. Anyone know what it is for this compressor or how to calculate it? "

That is a basic compressor spec and should be on the compressor, in the manual, or at the manufacturer's website. Failing that, take a look online at similar compressors and you will get an idea of the possible CFM range. A compressor the size you' re talking about is not going to be anywhere near 10-25 CFM.

I blow my system out with an old Sears one that puts out 6.6 CFM at 40 PSI, with maybe a 10 gallon tank. It's not ideal though. I go through the zones twice. Each time I let the compressor build up to about 75 PSI, then turn on the zone. The compressor can't maintain that pressure, so it starts dropping. But it does a good enough job.

[Stuart Benoff]

The sprinkler company says that it takes between 10 and 25 CFM to properly blow out the sprinkler lines. I have a 4 gallon/125psi compressor but the specs don't include it's CFM rating. Anyone know what it is for this compressor or how to calculate it?

Thank you.

[Stuart Benoff]

I was thinking that it should be a "basic" spec but I can't find it anywhere (manual, compressor or the website). It's a Husky FP2021 and I bought it from Home Depot.

Thanks for your help.

[chocolatemalt]

Indeed it seems the CFM and pressure output numbers for that compressor are nowhere to be found -- probably because they're horrible. But it's just a small portable unit so that's understandable.

Likewise, I have a portable Porter Cable compressor that seems nice and solid and delivers 6 CFM @ 90 PSI, but it's inadequate for blowing out sprinklers. Like trader4's experience, I can let it build up pressure then try to "surprise" the zone with a fresh blast of air, but it's gone in a few seconds and the motor is chugging along while the heads are blowing out a little air and no water. So I disconnect and wait for a re-pressurization for the next "surprise". With 2 or 3 interations per zone, the heads seem to get cleared. Concerned about the 50% duty cycle of the unit and not too keen on burning out the motor, I give it 10 minutes on and 10 off... and it takes at least an hour and a half of tedium to blow out 8 zones. I'm not sure if I'll slog through it again this year or pay $20-30 for the pros on the truck.

I suspect you really need a $500-$1000 compressor to really get the job done, i.e. one of those hot-water-heater-sized monsters.

[Edwin Pawlowski]

Most small compressors are 4 to 5 cfm, When you hit 25 cfm you are looking at a rather large compressor.

[Stuart Benoff]

Thanks for the feedback. I guess it's the distance of the sprinkler lines that makes the difference because this compressor was good enough to blow out the lines in my inground pool (well, at least I think it was but won't know for sure until I try to open it next spring). And, for the record, they charge about $65 in my area to blow out the sprinkler lines.

[cod]

If they charge $65, I will hire them. My current servicing company wants to charge $150 or more for one-year service deal, starting up the sprinkler in the spring, checking the system once in the summer and winterizing the system in the fall.

I was thinking of doing it by myself next year and found out that I could rent a compressor delivering about 8.9 CFM for $54.00/day.

I am not sure I can find a service outfit that is wiling to do winterizing only.

By the way, I live in a Chicago suburb.

[trader4]

"Dumb question, can you blow out one sprinkler zone at a time. "

Yes, and that's usually the way it is done. For one, that;s how most controllers are set to operate. Second, it can be done with less CFM.

[Terry]

Dumb question, can you blow out one sprinkler zone at a time. Also agree most small 'plug into a wall outlet' compressors have limited cubic feet per minute capacity probably nothing like 10 to 20 cu.ft/min.?

[Don Young]

[rdglide03-dbasedos]

If they include repairs on any leaks in the spring, this is cheap. What's the company name? I also live on North Shore.

[Stuart Benoff]

I figured out that my Husky 4gal 135psi compressor is only capable of

0.8 SCFM so I may try it just for the heck of it but I'm not very confident that it will be able to completely clear the lines. I think someone said that most home compressors have between 4 and 5 SCFM. And, as mentioned, the correct process is to blow out one zone at a time but the distance between where the compressor gets connected and the last sprinkler on that run be in excess in 125 ft so the compressor needs to hang in there for a while.

[Chris Lewis]

According to Stuart Benoff :

That compressor _will_ do the job... But it will require some care.

The length of the lines doesn't matter as much as technique.

The commercial rigs shove very high volumes of relatively low pressure air, so much so, that they can maintain full air flow continuously.

You can't do that with a home compressor. You have to do it in "shots", and wait for the compressor tank to recharge.

Secondly, abrupt pressure changes can blow your lines apart - the commercial rigs don't deliver that much pressure, but a home compressor can. So you have to be careful in regulating air flow.

With my original home built compressor (4gal, capable of about 1 SCFM at

100PSI), it used to take 3-4 "shots" to clear a circuit. Secondly, I had a full aperture ball valve to permit me to slowly build air pressure in the lines, not cracking it open abruptly for fear of blowing the connectors apart, and waiting until I got air from the heads before (gently) opening up the valve any further. Having a pressure guage on the line helps.

I replaced the 4gal with a 10gal, and I can do it in 2 or 3 "shots" now.

As another point, you can make things go somewhat faster if you can "lock down" the sprinkler heads on all but the last head in the circuit (or, last N heads if it branches). Ie: by placing a brick on them. More concentrated push to clear the whole line before the small amounts of air needed to clear each fixture. But that's a lot more trouble/time, and I don't need to (even on the circuit with 13 pop up spray heads, or the other circuit with 4 pop up gearheads).

[Stuart Benoff]

I'll try locking down all but the last sprinkler head as you suggested. I also have a pressure valve on the compressor so I can slowly release air into the line until the last head on the line pops. Maybe I'll even move one brick at a time to release one head at a time to maximize the volume of air but still keep the pressure low.

Thank for the idea!

[Chris Lewis]

According to Stuart Benoff :

You'll need to experiment - I tried the brick trick, but they wouldn't stay where they were placed ;-) More importantly, you really do need to be careful slowly moderating the pressure.

In my case, the irrigation system is fed via a hose bib with a copper wye instead of the male hose thread. One side of the wye goes through a ball valve to a male garden hose connector thence to an ordinary garden hose reel. The other side of the wye goes to a universal fitting (so I can disconnect the irrigation system completely), a one-way check valve and thence to the irrigation lines.

I made up an adapter (M fitting to hose female connector). I disconnect the garden hose, and connect the air hose adapter in its place. Shut off the water inside the house. Then the garden hose's valve becomes my control valve for pressurizing the irrigation system by backfeeding air through it.

Once I'm finished, I disconnect the irrigation system at the universal and tape a plastic bag over the end to keep out the grit and critters.

Alternately, you could make up an adapter from your irrigation feed end to your compressor.