# Connecting air compressor to irrigation



## Movingshrub

Anyone found any easy way to attach their air supply line to the sprinkler system? I've got 1.25" pipe. All the solutions I've come up with involve way too many adapters and bushings to get down to my air hose coupling of 1/4".


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## chrismar

My system came with a hose bibb directly after the PVB. I hook up my compressor to that for blow outs. I've seen people hook up to the test cocks too, but I've personally never tried.


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## William

Winterize Sprinkler Systems And Outdoor Faucets: Air Compressor Quick-Connect Plug To Female Garden Faucet Blow Out Adapter Fitting (Solid Lead-Free Brass) https://www.amazon.com/dp/B017CKUKHS/ref=cm_sw_r_cp_tai_hI3dAbTQP8E3B

This might be a good idea.


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## Movingshrub

Thanks for the input. My system is on a separate supply water meter, and I didn't install a water hose bib, so unfortunately those aren't viable options at the time.

I installed my valves between unions. 
So I piece together something that could mate to one of the unions, as a trial run for my solution and air compressor.


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## Ware

I don't think blowing the system out is very common in the south.


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## J_nick

Here is my set up. Mainly just used spare fittings I had laying around.


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## MasterMech

Movingshrub said:


> Anyone found any easy way to attach their air supply line to the sprinkler system? I've got 1.25" pipe. All the solutions I've come up with involve way too many adapters and bushings to get down to my air hose coupling of 1/4".


How handy are ya? If you can adapt a 1 1/4" slip joint to 1 1/4" female threaded pipe, then just drill & tap a threaded PVC plug for 1/4" NPT and install a male QC nipple.


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## Movingshrub

Ware said:


> I don't think blowing the system out is very common in the south.


I am inclined to agree. However, I have sprinklers with the rainbird SAM check valves. I wasn't sure if that would present an issue or not. With that being said, here is where I got to this evening.


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## Movingshrub

I managed to hook it all up and use an undersized compressor to blow out the system.

The CFM of the compressor I have it about 4cfm. Based on how blowing out the lines went, if's time for a higher CFM compressor.

Any idea how to determine what size compressor is required? One website said take GPM and divive by 7.5 to come up with CFM, but that seems inaccurate. I can change nozzles on everything and dramatically change the GPM.


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## MasterMech

Movingshrub said:


> I managed to hook it all up and use an undersized compressor to blow out the system.
> 
> The CFM of the compressor I have it about 4cfm. Based on how blowing out the lines went, if's time for a higher CFM compressor.
> 
> Any idea how to determine what size compressor is required? One website said take GPM and divive by 7.5 to come up with CFM, but that seems inaccurate. I can change nozzles on everything and dramatically change the GPM.


I'm all for buying a bigger compressor (insert Tim Allen grunting) but hopefully it's not just for blowing out the irrigation. Changing your nozzle flow to flow less air won't help either. You want to push as much air as possible through the system. I'd be looking at options like hooking up an accumulator or surge tank to get a big temporary blast or renting a big compressor for a half-day or less to get the job done quickly.

For BIG systems, we hooked up a big 100-200hp diesel compressor and charged the system. Then opened the drain(s) sequentially and let 'er roar. Blowing through the heads is only necessary if you want to confirm the zone is dry or you know you have low spots in your piping that hold water.


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## Movingshrub

I've got a small air compressor that will do 3.7 cfm at 40psi. It took me quite a while cause I didn't want to overheat the compressor.

Locally, I can rent a 210 cfm, 185cfm, and another that will do 14cfm.

I'd be willing to upgrade from my $75 compressor to something more robust so I can run an impact gun, an angle grinder, and other garage tools, while also being able to blow out the irrigation system. I'm in no hurry to replace the compressor - I really am just trying to discern what CFM compressor I would need to run the tools and blow out the sprinkler system.


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## chrismar

Movingshrub said:


> I'd be willing to upgrade from my $75 compressor to something more robust so I can run an impact gun, an angle grinder, and other garage tools, while also being able to blow out the irrigation system. I'm in no hurry to replace the compressor - I really am just trying to discern what CFM compressor I would need to run the tools and blow out the sprinkler system.


I have a 27 gallon craftsman compressor that does 6 or 7 SCFM at 40 PSI. I've used it to winterize my pool and irrigation system as well as run an angle die grinder and impact driver. I also use it to blow up tires and pool inflatables. It's an indispensable tool in my garage and probably one of the best purchases I've made. It's paid for itself already in the 2 years I've had it, in the pool closing and irrigation blow out costs alone.


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## Movingshrub

chrismar said:


> Movingshrub said:
> 
> 
> 
> I'd be willing to upgrade from my $75 compressor to something more robust so I can run an impact gun, an angle grinder, and other garage tools, while also being able to blow out the irrigation system. I'm in no hurry to replace the compressor - I really am just trying to discern what CFM compressor I would need to run the tools and blow out the sprinkler system.
> 
> 
> 
> I have a 27 gallon craftsman compressor that does 6 or 7 SCFM at 40 PSI. I've used it to winterize my pool and irrigation system as well as run an angle die grinder and impact driver. I also use it to blow up tires and pool inflatables. It's an indispensable tool in my garage and probably one of the best purchases I've made. It's paid for itself already in the 2 years I've had it, in the pool closing and irrigation blow out costs alone.
Click to expand...

Thanks. The math I saw was to take the rated GPM of the zone, and divided it by 7.5, to give you the CFM requirement to blow it out. My system uses 1.25" pipe, which seems like a lot of space to fill with air. The highest GPM zone I have is 25 GPM, so allegedly, a 3.33 CFM compressor should have done the job, but it seemed lacking. Also, I don't think the GPM to CFM calculation really accounts for the length of your pipe runs.

I think next year I'm going to rent the 13GPM compressor and see how that does.


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## g-man

That math is only correct for incompressible fluids. One cubic feet of water is 7.8 gallons of water. Air is a compressible.

The CFM needed will depend on your system/layout. For example, let assume your 1.25 in pipe is buried at 8in on a flat yard, but there is a section going underneath the sidewalk. This section goes down to 12in and then back up to 8in for each of the heads in the side walk.

When you first turn on the compressor and the pipe is full of water, it will push the water until there is a path for the air to go thru the pipe. Once the compressor airflow drops, it wont be able to push the water from the 12in deep section up to the 8in section and then up to the head. Water will likely travel back into the 12in section. You could recharge your tank and flow compress air again, but unless it has enough velocity and duration to lift the water from the 12in deep, water will remain in this section.

This is the best image I could find that shows what I mean (but think of it as a pipe in your yard).








The water in the bottom of the left side of the image will remain there if there is not enough CFM to push it out. This water could freeze (if the ground temp drops below 32F at that depth).


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## Movingshrub

Understood.

I just wish there was an easier way for me to figure out the CFM requirement other than just "a lot." With that being said, I really don't care if there is some water remaining in the pipes. I'm in North Alabama and I buried most of the lines 18" deep. I was primarily concerned with water remaining in the irrigation head themselves due to their integrated check valves. The run along the sidewalk was the only area where I wasn't able to bury 18" deep; I got to 12"-14" there. Using the air compressor, I blew out each zone to where all the heads were simultaneously blowing out just air rather than just mist. I'm going to count this as a success unless proven otherwise in the spring.


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## g-man

Oh! You should be more than fine. Remember, it needs to get below 32F for some time at the 12-18in depth. Plus there needs to be enough water to hard freeze and push on the wall of the pipe for it it break. North Alabama frost line is 10in, you should be fine.


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## AvidGolfer

Found this post SEVERAL years later... but wanted to share a bit of information.

It wouldn't be necessary for you to blow out ALL of the water. While it is best, if you have residual water in the bottom of the pipe, it would be okay. As you know, water expands (about 10%) as it freezes (freeze a sealed soda bottle to see). If you get the majority of the water out, you would be okay.

The important issue is leaving room for water to expand. If the pipes are at least half empty, you should be safe. However, the caveat is your pipe is not likely level. This means water will pool at the low lying areas. As long as this isn't a valve or sprinkler head, you'll be fine. If it is, you can leave these "on" or in the open position and allow for expansion through the valve. Just don't close it until after a thaw.


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## jtuber

Maybe running in some antifreeze thru the lines to help with freezing?


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## AvidGolfer

Ethylene glycol is bad for grass. Good thought though!


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## jtuber

This is not bad for grass, propylene glycol


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## SOLARSUPLEX

Its common in the aftermarket auto industry for air ride suspension to include a small amount of air brake antifreeze prior to the cold months to stop valves from freezing.

 CRC Air Brake Anitfreeze 

The main chemical is Methanol which is applied in foliar apps according to  this study  "No significant response, either beneficial or detrimental, to methanol application was found in any crop."

Somebody tell me I'm crazy but these all seems like you'd be good to put a bit in the system - then blow it out and whatever remains will be mixed with the water that is left over and aid in preventing freeze.

As for how much, well that comes down to assuming you know how much water remains in the system and how cold you anticipate the ground being. This chart could help. The bottle I linked was 32 oz. If using the entire thing and assuming there is 1 gallon of water left in your system, you'd be good down to around -20C.

In the study linked above they added either 200 mL Methanol to 800mL water or 400mL to 600mL and sprayed. With the dilution of the lower end being 1:4 that comes out to the same ratio as the 32oz in 1 gal of water i assumed..

Am I going to do it? nope, i just blew my system out yesterday and worked fine since my runs are so small.


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## AvidGolfer

https://www.tandfonline.com/doi/abs/10.1080/15226514.2010.525553?journalCode=bijp20&

https://cfpub.epa.gov/ncea/pprtv/recordisplay.cfm?deid=339126

https://www.michigan.gov/documents/deq/deq-ead-tas-antifrez_320830_7.pdf

Methanol (is a one-Carbon) alcohol. It is also extremely toxic. Causes neurotoxicity and blindness if ingested. Having said that, it is nowhere near the same thing as propylene glycol. Two completely different compounds and are achieved through different chemical reactions.


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## SOLARSUPLEX

AvidGolfer said:


> https://www.tandfonline.com/doi/abs/10.1080/15226514.2010.525553?journalCode=bijp20&
> 
> https://cfpub.epa.gov/ncea/pprtv/recordisplay.cfm?deid=339126
> 
> https://www.michigan.gov/documents/deq/deq-ead-tas-antifrez_320830_7.pdf
> 
> Methanol (is a one-Carbon) alcohol. It is also extremely toxic. Causes neurotoxicity and blindness if ingested. Having said that, it is nowhere near the same thing as propylene glycol. Two completely different compounds and are achieved through different chemical reactions.


So you're suggesting spraying it in the air within a neighborhood isnt best practice? :lol: :lol:


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## AvidGolfer

:lol:


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## RVAGuy

AvidGolfer said:


> water will pool at the low lying areas. As long as this isn't a valve or sprinkler head, you'll be fine. If it is, you can leave these "on" or in the open position and allow for expansion through the valve. Just don't close it until after a thaw.


This is nonsense. Water in a pipe will burst the pipe, it happens all the time. And leaving the valve "open" does not allow for expansion through the valve. By the time the water freezes, it's ice and won't form into any open space in the valve. The best way to not burst a line is to get all the water out. Period.

You also need a big rental compressor (or just pay someone). Hunter recommends 80-100 (!!!) CFM. The engineers know what they are talking about vs backyard recommendations.
https://www.hunterindustries.com/winterizing-your-irrigation-system


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## RVAGuy

SOLARSUPLEX said:


> Its common in the aftermarket auto industry for air ride suspension to include a small amount of air brake antifreeze prior to the cold months to stop valves from freezing.
> 
> CRC Air Brake Anitfreeze
> 
> The main chemical is Methanol which is applied in foliar apps according to  this study  "No significant response, either beneficial or detrimental, to methanol application was found in any crop."
> 
> Somebody tell me I'm crazy but these all seems like you'd be good to put a bit in the system - then blow it out and whatever remains will be mixed with the water that is left over and aid in preventing freeze.


I have also checked this out. It's relatively safe as we're not drinking the stuff like they do on the MSDS tests. I worked on trucks for 10 years with frozen brake lines and the stuff works great.

It is compatible with PVC and valve seals, from what I can find, however what keeps me from pulling the trigger is the corrosion inhibitors they add to the methanol.

IDK what the corrosion inhibitors are and if they're good for grass. Keep in mind too, this won't be a large amount at all. The way to apply it would be to add it to the compressor tank and let it boil/evaporate in the tank while the system is being blown out.


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## yesitsme

is it ok to connect the air hose to the irrigation system before the PVB? would it do any harm to the PVB if i keep it at 40~50 PSI


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## Lust4Lawn

RVAGuy said:


> I have also checked this out. It's relatively safe as we're not drinking the stuff like they do on the MSDS tests. I worked on trucks for 10 years with frozen brake lines and the stuff works great.


I think you have WAY too much faith in your sprinkler system's ability to prevent backflow. Putting anything with even the slightest potential for toxicity or harm into your sprinkler system hooked up to a pubic domestic water source or shared aquifer is extremely irresponsible.

You are completely overthinking this. Blow the sprinkler system out properly with enough air and call it a day. If you don't have that ability, is saving $75 worth hurting or killing someone?


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## Utk03analyst

Thought I would share my experience and cover an additional item. I'm in the south Nashville and I blow out my system myself. My lines are not super deep about 8 to 12 inches. The frost line for TN is 12 to 18 inches. So my lines would potentially freeze.

I've read about scfm. But an additional item is psi and the running hp of the compressor as well. The higher the hp normally the faster the compressor tank fills to help maintain the psi. Most nozzle charts start around 30 psi. In order to flow out all of the water the compressor would have to maintain roughly 30 to 40 psi.

My setup.





I put my system in myself I have a drain just after the ball valve that connects to the meter in the front yard. I open the drain to drain the water from the back flow to the connection to the main line which is about 2 feet deep. Then I turn off the valves at the back flow. I don't connect to the back flow never tried but I installed a spigot between the back flow and the first manifold which is where I hook my airline too.

Depending on the zone my compressor can keep 50 psi for 3 minutes once fully charged which depending on the zone is long enough to go from water, to mist to straight air.



I have 13 zones. It sucks doing one zone at a time but it gets it done. I usually do half one day half the second day and on day three just test to make sure everything is cleared out. This is my third season and I didn't have any problems the first 2 years. I wouldn't personally add a chemical through my line. I also don't think it's necessary to be 100% free of all water but I'm no expert just speaking to my experience.

I had an older craftsman air compressor that was a beast the running hp of the motor was awesome and it filled up super fast one day I'll upgrade but the running hp of the motor is a super critical number for me.


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