I want to run air lines in my garage using pipe to make getting air a little more convenient. Anything special need to be done at the pipe joints so I'm not leaking air through them at 150 psi?

 

my first question would be, Why do you need 150 psi air lines? You can regulate your pressure off of a manifold line or off the tank down to a more 'workable' pressure. If you MUST have 150 psi then you should go for high volume black iron pipe with schedule 40 wall thickness. Depending on the run, 25 ft or more use 1 1/2" and then reduce size from their to your work station. Pipe joint has a tapered fitting which gets snugger as you tighten it, use teflon paste on the joints. Make sure you wipe the inside of the pipe down with thinners to get rid of the mill oil. A coat of gyptol paint makes a durable finish on the inside and prevents rust and scale deposits from forming in the pipe on horizontal runs.

 

Schedule 40 Iron pipe will work well. Just don't try to use PVC pipe. It won't last! Also if you are going to bury it underground use schedule 80 or it will end up breaking and leaking where you can't find it. Also for compressed air the only sealant to use is locktite pipe sealant. will not set untill the joint is tightened up and will be leaktight. In order for the joint to leak the fluid must follow the the root diameter of the threads out. All you need to do is interrupt that path in only one place. It is not necessary to coat all the threads, all the way oround the pipe, to effect a good seal. All that is necessary is to apply the dope to one side of the threads.

When installing pipe in the overhead, loop completely around the shop and back to the compressor. The exits from the loop for your drops should come out of the top of the loop then down to a convienient level with a dripleg at each station.

Condensation occurs when the air in your pipes cools and moisture in your air condenses to form liquid water. The trick to dry air is to cool it and drain it before the air gets into your network. Any further cooling in your pipes will result in more condensation. The slope in your piping will cary the water to the low point where you can drain it. Very little will get into your droplegs as they exit from the top of the loop.

Also if you are using a two stage compressor then 125-150 PSIG is a good operating pressure. In order to get adequet air pressure at the tool (100 PSIG) you must have an elevated supply pressure to overcome pressure drop across the piping network, fittings and/or filters.

If you are using a single stage compressor do not exceed 125 PSIG regardless of what the label might say on the machine. Above 100 PSIG the efficeincy drops off rapidly for a single stage machine.

Good Luck!

 

You really think he would need 1 1/2 air lines? For a small garage 1/2 is plenty for short runs of up to 100 ft, 3/4 if you are going to be running big air guns, 3/4 or 1 inch, which I doubt.

 

Not that I recommend it but I ran 3/4" schedule 40 PVC pipe 100 feet underground and under a dirt road about 10 years ago to get air from my shop to a paint booth. Haven't ever had any problems with it.


-EDIT- PVC can only be used underground, see Read First: at the top of this forum re PVC pipe. -Admin

 

why waste your time with black pipe in you shop? run 3/4" copper water pipe, sweat it like just like you would water lines and any threaded fitting, teflon tape and teflon dope, just be careful it is real easy to over tighten. you can even get away with 1/2" if the runs are 50'(more or less) and you don't plan on running jack hammers off it. most air hoses are 1/4" to 3/8" od inside. don't forget to put ball valves at all terminations and pitch it to drain. include blowoffs on the bottom of drops.

 

That is good solid clear advice, a 1/2 line will carry twice the air of a 3/8 no problem. When I sandblast I run 3 comps thru a 1/2 hose about 50 ft, with 2 it will run way more air thru it than I can make. Of course it isnt a sudden burst like a big air impact would need but with one realitively small compressor and one or 2 users in the shop 1/2 is plenty. I used 3/4 mains but I have some 100 ft runs and multiple users. 1/2 is fine especially if you are running hi pressure and regulating at the hose.

 

I use 3/4 copper for my main and 1/2 for branch lines works great and no rust.

 

Make sure you run the heavy wall copper, not the cheap stuff from the home box store.

 

even the thin walled type M is more than enough to hold the pressure.

check out Tables 3a, b, & c.
use hard pipe not rolls it will look better.

 

You may want to visit tptools.com and select the "Tips/Technical" section. In that section there is a PDF file called "Air line hookup - metal piping diagram". The file has alot of good info on designing/sizing your air line system.

Bob

 

Those were some great charts, thanks for the data. A number of users have said the M-type was not good for airlines but it looks to be OK according to those charts unless someone can come up with prohibitions. Of course the M-type sold at the home box stores may be the problem... -hehe! The solder used looks like a limiting factor also. The 50/50 tin lead derated the pressure but the other solders looked OK. PVC is rated for the pressures involved in compressed air systems but the material shatters and the lines explode like a fragmentation grenade so it is outlawed.

Remember also that using high pressure air and then regulating it down wastes the energy it took to compress the air to the higher pressure.

 

You are right about it being a waste especially if you are hooking a hose right from the comp,,, but for most people the cost would certainly be insignificant and hi pressure makes transfer more effecient and reduces line losses and secondary pressure drops when demand is high. I regulate at point of use.

 

Type L copper pipe is available at the big box stores, and is the same vendor as sells to plumbing stores. I've used it for air lines, no problem.

 

I gave a formula in another thread here recently on energy loss thru regulation. It can be significant when the difference in pressure is high like 150 down to 90PSI.