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Discussion Starter #1
Has anyone ever seen an affordable PTO driven air compressor? I always have a tough time blowing out my sprinkler system in the fall beacuse of its location. The manifolds are in different locations around the yard so we end up dragging 3 portable electrics around and they just dont have to cfm to hold the heads up properly. I am not having any luck locating a portable pto driven for the tractor, but maybe they don't exist? Any help would be appreciated. Thanks!!
 

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Surplus Center

There's a business that I believe is called SURPLUS CENTER. Never ordered anything from them, but used to get their catalog. If that is the correct name, they might have the parts and hardware you could build one yourself. They used to have either entire military surplus PTO generators and/or the parts to build one. I know they had all kinds of hydraulic cylinders and airplane generators, and much, much, more. Think I recall seeing several types of air compressor pumps in the past.
 

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Discussion Starter #3
Thanks for the info! I will look into that, but unfortunately I am not so handy to be able to build my own. I was looking for a ready-made unit.
 

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Surplus Center is the name of the place. I've ordered from them before.

Here's one that has a max RPM of 800. You could run it at the 540 PTO speed, and the CFM would just be lower. You'd need a mounting arrangement, PTO coupler, air tank, pressure regulator, and some fittings to make it work.

Surplus Center - 30.16 CFM AIR COMPRESSOR SINGLE STAGE 5 HP

I don't think you will find a dedicated PTO-driven compressor for under $2000.
 

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Discussion Starter #5
pto air compressir

Andy, I took a look and this compressor seems like it would do the job at 30 some cfm. I assume you just get rid of the flywheel and replace it with the pto coupler? Do you think this would be a pretty involved project?
 

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I would think the cheapest way would be to rent or purchase a large nitrogen cylinder. Especially if you will only need it annually. Biggest benefit is...You could dial the regulator up to the output needed to clear the lines (max about 2000psi,but you'll not even come close to needing that high of pressure,nor will your lines handle it).
 

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I rent a diesel powered trailer mounted compressor every year to blow out my lengthy system, and I do a friend's too. It has plenty of grunt (185 CFM) to blow out the lines and I regulate the pressure to about 70-PSI to protect the pipes.
 

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I would think the cheapest way would be to rent or purchase a large nitrogen cylinder. Especially if you will only need it annually. Biggest benefit is...You could dial the regulator up to the output needed to clear the lines (max about 2000psi,but you'll not even come close to needing that high of pressure,nor will your lines handle it).
I would think your nitrogen bottle would freeze up at the flow rates needed to do this job...
 

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Discussion Starter #9
pto air compressor

I'n not familiar with the nitrogen option?? I am familiar with renting the trailer mounted units. Things like that are extremely tough to rent in North Dakota beause of the oil activity. If you can fine one to rent, it will be very expensive. That is why I was trying to find one on my own. It would be paid for in a couple years worth of rentals.
 

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Since you already have a fairly large 3 pt generator, maybe pick up a big electric compressor and mount on a small trailer. You may have to mod the trailer to have clearance for the PTO generator. While it does not seem to make a lot of sense to use a generator to make electricity to turn a motor to compress air, it may be the most cost effective approach. Then, for the rest of the year, you will have one heck of a compressor to use in the garage.
 

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Andy, I took a look and this compressor seems like it would do the job at 30 some cfm. I assume you just get rid of the flywheel and replace it with the pto coupler? Do you think this would be a pretty involved project?
You know, actually, it may be even simpler than I was thinking.
Yes, you would just get rid of the flywheel and get a PTO coupler.
I was thinking of the tank and regulators and fittings and all the other "normal" compressor junk. But in reality, all you want to do is have a compressor to flood the lines with air and shove out water, correct? Well heck, just have a connection on the compressor that you can hook between the compressor and your sprinkler water lines. Hook the line up, engage the PTO, and flush the water out. Once the water is gone, shut off the PTO. You really don't even need the tank, although a regulator may be needed if you don't think your sprinkler supply lines will handle it. You'd need to bleed off excess pressure somehow because you don't have a tank, but a simple ball valve and tee would work.

I would think you could get the PTO coupler and airlines for less than $100. You would still need a friend to make the mount to hold the compressor on the back of the tractor (a drawbar mount would be simple, like I did for my log splitter pump), but the entire project should cost under $700. Not real cheap, but much cheaper than any PTO compressor you're going to find.

Of course, as jnelson pointed out, you have a big PTO generator at your disposal. If you can find a normal electric compressor that will work for under $700, you could use it for other things than just clearing water lines.
 

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Discussion Starter #12
pto compressor

I have thought about the big twin cylinder 60 or 80 gallon compressors also but those are not cheap either! I really like the idea of just getting a compressor that has enough cfm to just clear the lines and have a way to regulate or blow off the excess as you suggested. I dont think those big trailer mounted units have tanks?? Do you think 30 fcm would be enough to hold those lines at about 60 psi even when most of the water is out? That is when the small electric compressors run out of steam. They hold the heads up while there is some water, but as soon as the line is mosttly clear, they drop and wont flush fully. What do you think about 30 cfm being enough??
 

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Trailer mounted compressors don't have storage tanks like shop compressors do. How many feet of sprinkler lines are you looking to blow out?
 

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What do you think about 30 cfm being enough??
If this question is directed at me, I have no idea.
So if it was me, and once the heads start popping up they use too much air, I would just have a bunch of patio pavers and walk down the line and once the air starts shooting out the sprinkler head closest to me, I would stick a paver on it to hold it down and walk to the next one and so on. That way the water will be flushed out to the farthest head at the end of the system. Of course, I don't know if a paver would hold the head down, or if it would break it.
 

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Discussion Starter #15
PTO air compressor

Trailer mounted compressors don't have storage tanks like shop compressors do. How many feet of sprinkler lines are you looking to blow out?
The lines are quite long. The lines I have troble with are maybe 400' with 6 heads.
 

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Discussion Starter #16
If this question is directed at me, I have no idea.
So if it was me, and once the heads start popping up they use too much air, I would just have a bunch of patio pavers and walk down the line and once the air starts shooting out the sprinkler head closest to me, I would stick a paver on it to hold it down and walk to the next one and so on. That way the water will be flushed out to the farthest head at the end of the system. Of course, I don't know if a paver would hold the head down, or if it would break it.
Sorry Andy, I still learning how to use this forum so I apologize for being a bit confusing. Yes, I was asking you what you thought about the 30 cfm. I really do like yuor idea about getting a compressor from Surplus Center and mounting it to a 3 point skid or something of the like. By holding the heads down, they still expell air, albeit down in the base rather than out onto the grass. I know the commercial compressors can hold them up easily. I just need to figure out exactly how much cfm is necessary to hold them all up at the same time. I know that tractor has plenty of power, its just compressor size that is the unknown to me.
 

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I would think your nitrogen bottle would freeze up at the flow rates needed to do this job...
The outer bottle will eventually freeze up from pressure drop.But this alone doesnt stop flow, it just lowers bottle total pressure. But even if it lowers the bottle pressure to a quarter of its static (ambient) temp/pressure. You would still have over 500 psi. I pressurize very long / large line sets ( 3" plus)
pretty often . I don't think this would be a factor unless he let it flow for very long periods. I just wanted to give him a cheaper alternative that could be adjusted easily for enough output to clear his lines. Last time I. Filled a 120 cylinder it was around 45 dollars. That should give him a least 2-3 yrs of capability before needing refilled ( depending on length and number of heads etc)
 

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Discussion Starter #18
PTO air compressor

I had no idea a nitrogen cylinder could be used for this! How large would the cylinder have to be to accoomplish about maybe a half hour of run time? Also, would there be a risk of freezing the manifold at that long of a run time?
 

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Andy, I took a look and this compressor seems like it would do the job at 30 some cfm. I assume you just get rid of the flywheel and replace it with the pto coupler? Do you think this would be a pretty involved project?
I doubt that would work. The large pully on an aircompressor has a shaped spoke to cook the compressor. You would have to check the pulley reduction as well to make sure you drive the pump at right RPM. Not to mention you really need a tank unless you have one huge pump.
 

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The lines are quite long. The lines I have troble with are maybe 400' with 6 heads.
I have some lines on the order of 400' or more in length that are used for irrigating trees, and I seriously doubt 30-CFM will be enough depending on how much air escapes through each head.

I have a Crapsman compressor similar to this one. Craftsman 20 Gallon Vertical Air Compressor - Tools - Air Compressors & Air Tools - Air Compressors I tried it one year to blow out my lines, and it ran constantly, and I never could get all the water out of the lines, which resulted in some localized freeze damage to the system. Notice how puny the CFM output is on the Crapsman. An I-R 60-gallon compressor has just under 15-CFM Ingersoll Rand 60 Gallon Industrial Air Compressor, Vertical Tank, 5 HP, 2 Stage Pump - Tools - Air Compressors & Air Tools - Air Compressors according to Sears, which is better. In any case, the 30-CFM of the Surplus Center compressor is better yet.

Now for giggles I calculated how much uncompressed air is in a 3/4" x 400' line and I came up with this number. (0.375^2) * Pi = 0.44 square inches of cross sectional area. 0.44 x 12 = 5.30 C.I. per foot. 5.30 C.I. x 400' = 2,120.6 C.I. 2,120 C.I. / 12^3 = 1.23 C.F. in that 400' run of pipe. Obviously that's not much volume and one would easily surmise that a puny compressor could blow out that much water; but that volume is for uncompressed air, and does not take into account compression ratios, amount of air escaping from the heads, pipe size, friction losses in the pipe, etc.

The trailer mounted compressor I rent pumps out 185-CFM and I have it regulated to 70-PSI. My irrigation system has 1" pipe for the main header, with 3/4" pipe for each zone branching off at various distribution manifolds. At each tree, I have a 1/2" pipe coming out of the ground with a 1/4" drip line regulated to 24-GPH attached to the 1/2" line. At each tree is a 1/2" valve that I turn off to force the most amount of air I can for each drip line. It takes me about 30-minutes per zone to get the lines blown out to where I feel comfortable that freeze damage won't occur. My air system is 1/2" copper and was sized with my puny Crapsman compressor in mind. I use 3/8" air hoses to connect the rental compressor to my air system.
 
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