CU air lines for home shop - what diameter?

A smooth 1/2" air line at 100 psi will carry 40 cfm with a 5 psi pressure drop in 100 feet. There's barely a need for 3/4" nevermind 1". The only practical reason for using larger than 1/2" is to increase the storage capacity of your plumbing and also its ability to condense water out of the air. The latter only works if your system is plumbed with pitch and condensate collection stubs.

Bob

Larger is better, but 3/4 should be plenty good for you. Plan ahead for the items to connect the line to your couplers. If you wait until the last minute you may be stuck in the 5-to-do-what-1-would-do mode of any plumbing type of job. A threaded tee should be all you need to put in place to screw in your coupler. Often the particular tee you want will conveniently be on back order. That, by design, IMO. Make sure you do something to keep water out of the system, there was lots of good information in this group recently. IIRC, Roy Hauer had a pretty good setup. I have a second tank that is larger than the main plumbed inline, allowing the air to expand and cool which works very well. Prior to getting that tank, I had a small, portable sized tank inline which was in an old refrigerator. That worked very nicely. Stopped using that only to consume, and pay for, less kilowatts. Your local conditions regarding humidity will dictate what you need to do. Eventually you will certainly have occasion to use more than 1 drop at a time. Look at it in the same light as the "space available/how much can I collect" mindset.

michael

I used 1/2" air hose to plumb my shop, it has worked flawlessly for years and still looks neat and brand new. Much less trouble to install than any kind of pipe. If you want 3/4" or even larger, that is available also but the 1/2" works great for me.

Vaughn

I've put several small runs of 1/2 copper pipe in my shop, and they seem to work fine. Maybe if you were going to run air tools with high CFM ratings you might want to size up to 3/4.

Jim

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I ran some hose, too. Just 'till I get around to plumbing for real. It works fine, but I'm wondering: doesn't condensed water tend to accumulate in the inevitable dips in the hose? I haven't seen any sign of it, but I'm not sure what the signs would be.

Bob

On Wed, 17 Dec 2003 22:52:35 -0500, aribert brought forth from the murky depths:

If you want more volume, add a tank. If you use a quick disconnect and gate valve, you can add a 7gal portable which could be used in all sorts of weird places, including in the truck (You don't drive a mere car, do you?) on the road, in a field, etc. Very handy. I have QD females on 8' and 50' hoses from my portable tanks and use double males to connect it to the main line in seconds for filling or storage.

-- Remember: Every silver lining has a cloud. ----

Snipped bor brevity

IIRC, Roy Hauer had a pretty good setup. I have a second tank that

Please tell me one more time, if I have two tanks in my system, how the air is expanding into the larger tank ... ???????

If the are connected together by any reasonable sized piping the pressure in both should be the same. If I have 150 psi in the first tank connected to the second tank with 150 psi.... ???

Thanks in advance for clearing this up for me.

Pete

Would you please quote the formula you used and a reference? TIA

Ted

Sorry about my ignorance, but what is the danger of using PVC for this.

Thanks

Barry

Shatters sending sharp shards places you don't want them. Copper won't.

Lane

I had a chart somewhere....but if I recall the 40cfm is a bit over from the info I had. I think it was closer to 18cfm. At any rate for "normal" hand air tools 1/2" is plenty. In a shop I had a few years bad I had 1/2" ran for over 100 feet. With the highest cfm tool in my collection the pressurer guage at the end of the run would not even wiggle when the tool was run. Greg

We never got around to permanent plumbing in our machine shop. Dad suggested we use copper water line.

I understand it plumps faster than pipe, but I have concerns about vibration and pressure cycling causing work hardening and subsequent cracking.

Yeah, I know you can isolate the viration from the compressor with a soft line, but I still wonder...

Comments?

Put a hose between the compressor and the lines to isolate any vibes. It really is not a problem anyway! I work on HVAC equipment. You should see how bad some AC lines vibrate in AC equipment! I have seen copper lines vibrating so bad you can barely see them! Just a blur! Rarely see a cracked one. Greg

Someone else can explain the physics. It works for me.

mj

aribert,

I looked in my Pocket Reference Guide and it has a chart of recommended air line size based on air flow and run length. All information that I am providing is for runs up to 50 ft. For flows up to 10 cfm it recommends a pipe size of 1/2". For flows from 11 to 35 cfm it recommends a pipe size of 3/4". Remember that these recommendations are for steel pipe and 3/4" Sch 40 steel pipe has an I.D. of .824" and 3/4" Type K copper pipe has an I.D. of .745". If you really want to work out this problem you could get some reference materials and do the pressure drop calculations, but for a run of less than 50', this would be overkill.

From the above information I would go with 3/4" copper pipe. Even if you get a bigger compressor and run air tools with higher air consumptions, or get a sandblaster, you will probably never have to re-plumb your system. My other recommendation would be to use Type L or M copper pipe. It is thinner wall so it would flow more air, it will easily handle the pressure, and it is cheaper. Here is a website with the pressure ratings for copper pipe:

Regards,

Ron

I was in the ceiling area of my shop a few years ago, banging on a 2x4 near a PVC piped air drop. Next thing I know, the pipe explodes about a foot from my face! How I didn't get hit by the shrapnel, I'll never know. Upon examination of the area, I found that a guy who helped me a little on the original installation had run out of thick wall PVC, and had grabbed a piece of thinwall to finish the drop. My new shop coming up will definitely not have PVC air lines even though I have been well served by them other than that incident for 22 years.

RJ

Thinking further about it, I suspect it be:

1. larger surface area avaialble from the tank walls.
2. Larger volume = lower velocity, droplets can not be carried as easily, and collect on tank walls, drip to bottom.

Any other explanations?

Pete

The implications of (1) are higher thermal conductivity to free air, thus improved cooling. - GWE