Pat, I think you'd be better off to get a separate air compressor as you will loose about 10psi per 50ft of line. In order to keep the lose down you'd need to up the diameter of your air line quite a bit and it would need to be rated at about 200+ psi (even though your air supply will probably be about 135psi.). Also those flexible lines unless there rated for outdoor/under ground will probably rot in a few years and you'd be doing it all over again.
Sorry, but I disagree. Here is why...
I will not be trying to "use" air from the long run of hose but will just be filling a tank in the barn via the long run of small hose which I bought a couple days ago (250 feet @9 cents per foot.) It will fit inside 3/4 inch conduit along with the 6-3 with ground wire power run. This little tube will fill the 30 gal tank (which I will cannibalize from a failed Devilbiss compressor) via its check valve. At stasis the flow rate is zero so the losses are zero. The dynamic losses are not of consequence since I don't really care a lot how slow the initial or subsequent fills are (hours wouild be acceptable as I don't need minutes. My needs for air in the barn are not too HD, just maybe topping off tires, things a portable air tank could do (sort of) but I don't have to tote it back and forth to a compressor or air line doing it this way.
If I really cared I'd bury a larger pipe.
In the event I have to do some HD air work like with impact tools this set up will not be useful. But neither would a little HF pancake or similar which costs more and is more maint and failure prone than a run of tubing. If I have to get serious with air I can just press the button on my electric start 17,500 Watt (continuous rating) generator which is mounted on the same little trailer as a 10+ CFM @90 PSI compressor and air too away. The genny has an idle control so when the compressor runs the genny revs up and when the compressor stops the genny goes to idle (likewise other loads.) It has an electronic governor so load response is very good.
I will feed the little line from a regulator set at 125 pounds or maybe a tad less (Devilbiss was set for 125 max.) My shop air is a 175 PSI 60 gal. My air dryer (refrigeration compressor type) is not rated that high so I have to set the output regulator lower before distributing the shop air.
I understand your comments and they are appreciated. If I were trying to actually use air as it was delivered by the little tube all your comments would be valid and my installation would be really stupid. The little tube was less than $25 plus a couple fittings vs always having to carry a "turtle" back and forth from the shop to the barn to have a bit of air in the barn.
Regarding rot: Note the plastic tubing I bought is not your typical beaided air hose with cloth fibers in it. It is like what is often used for ice maker water lines and is pretty impervious to being buried. Since it is being installed inside a PVC conduit with no light exposure (UV degradation) it should last for a very long time.
I'd like to acknowledge other well intended suggestions such as Soundman's too. If my requirements were as some of you supposed then my approach NEEDED help. It never hurts to get a sanity check before doing unusual things.
Oh by the way... why not direct burial wire since the air line would be OK for direct burial? Because direct burial wire costs $1.11 per foot more and conduit is $0.24 a foot. I will save about $0.87 per foot for a bit over 210 feet (less the cost of glue and a few fittings at the ends.) $174 (200 ft) less the cost of the glue and fittings makes it worth while to assemble conduit. I can have a lot of fun with the $150 + difference.
Pat
