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Shop Air Piping

DanH

Legacy Member
Mentor
Today's front page photo (Paul in Oz) reminds me...I ran across this illustration in the bottom of a drawer. It's from Sharpe, the spray gun people, the correct way to install your shop air supply.

The fundamental principle is simple. A long run of iron pipe cools the hot compressed air, condensing the moisture, which drops into on of the multiple drops spaced along the run.

My shop has 60~70 feet of 3/4 pipe prior to the drop I use for painting. Actually it tends to be a general use drop, as the long shop flex hose stays connected there. It all stays dead dry. I have a bead blast cabinet at about 50 feet, and it stays dry too.
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Yep. Mine is all copper, that I've been moving from space to space for the last 30yrs, with drops taken from the top, with everything sloping back to the source and blowouts at each of the six drops. I too have 70' to the "paint" location and also have no moisture in any drop in the shop with the compressor outside.
 
I was just thinking today - - and wondering what piping you were designing your new shop. I have 1/2" black pipe and had to rethread over 140 internal and external threads. They were lathe cut and stopped the rotation without withdrawing the cutter and made an axial groove on every single part. Further, after 35 yrs, it is beginning so spit rust chunks. So when you reach 100 yrs old it might give you trouble, but won't leak.

I first saw copper in a Delphi ECM factory, they did it to prevent Fe contamination. It was beautiful, and would well over the 175psi of most 2 stage compressors.
 
The next time I plumb for air, it will be with PEX.

That is much cleaner, faster, and cheaper. Considering you are the Gasman, I have to assume you know what you are talking about. I imagine it would cool the compressed air just as well as metal - maybe better in summer?

Thanks for the tip. When I painted my plane I did have some trouble with water in the line. I wish I had seen the Sharpe drawing before then!
 
Apparently PEX and other plastic pipes can bust violently and send shards of plastic flying at everyone nearby. Metal pipes burst in a much safer fashion.Just a split and no shrapnel flying throughout the shop. Copper pipe for me. My shop isn't big enough for the length of runs mentioned. Did the best I could with the small shop I have. Probably should have used 1/2" copper, and done double 45* elbows instead of 90* elbows. Maybe next time.
 
Apparently PEX and other plastic pipes can bust violently and send shards of plastic flying at everyone nearby. Metal pipes burst in a much safer fashion.Just a split and no shrapnel flying throughout the shop. Copper pipe for me. My shop isn't big enough for the length of runs mentioned. Did the best I could with the small shop I have. Probably should have used 1/2" copper, and done double 45* elbows instead of 90* elbows. Maybe next time.

While your statement may be true for PVC pipe, it is not true for PEX. PEX is found most everywhere, including professional shops…
 
The problem with PEX is UV. It just won't stand up to UV light. That and it's ugly.....

-Marc

A coat of latex paint will solve both issues.

PEX is so reasonably priced and easy to install it is worth the effort to paint it.

PEX will not shatter. It does need to be fastened down. In long lengths it can whip like an air hose if cut.
 
Hmmm...

PEX won't stand up to UV light? That may be the case but I don't know of very many folks that run their line in direct sunlight and the UV from a lightbulb is insignificant.

Pex is being used everywhere in construction, and I have yet to hear of a failure because of UV...
 
I can't quantify this because there's too many variations in materials. If using non-metallics versus steel/brass/aluminum tubing/piping, give yourself some margin in run lengths. The thermal conductivity will be less so the heat xfer will be proportionally less. I don't have the time right now to calculate the individual components of velocity/dwell time/cooling as they relate to air condition. Obviously this will matter more for high, more continuous, usage like blasting.

Side note (drift warning). It makes practical sense that PEX rupture is more benign that rigid PVC, CPVC, etc. Question for anyone who's gone this route for shop air. Were all of the fittings for equipment connection and such readily available or did it take a look of sourcing effort? Thx
 
I doubt the pipe material makes a lot of difference; use whatever you're comfortable with. Key points are simply lot of length for cooling, and a pipe arrangement to separate liquid water.

There is more than one way to plumb a system. In the Sharpe drawing, the main line slopes down for the entire run, and all the water supposedly runs to the last drop. The other approach is a level main line with water removal at each drop. It's more convenient to install, as it can run close to the ceiling. An upward turn to ensure air separation is relocated to the side of each drop pipe. The photo below is my shop some years ago, with a whole bunch of freshly painted biplane bits. You can see some of the air piping in the background.
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It has to matter some. As mentioned, it will be benign for low flow conditions; but, for high/continuous flow, it will affect the the overall Q. U being affected by material conductivity, among other things. Q=UA(LMTD)

In the end, the thermal driven potential is primarily affected by the (Logarithmic) mean temperature difference. In this case, the area between an inverse log function and a straight line (ambient). Don't get wrapped up in flow direction versus t and a graph. The area between the curves stays the same. While it the LMTD remains high, the specific heat of the associated mass flow inputs a lots of energy from the inefficient compression. Q=CpW(MTD). A quick energy balance, if you knew the inlet and boundary conditions, would provide the crossover point to do a new versus old length ratio.

That's from part of my life over twenty years ago as a system designer. If wrong, let me know. I'm not feeling challenged in the office today and don't mind re-learning something. In the end, will the material selection matter? In most cases = probably not. Adding some margin (length), especially when switching to less expensive materials, is relatively cheap.

Cheers boys.
 
I doubt the pipe material makes a lot of difference; use whatever you're comfortable with.


Dan, this is incorrect. I used to work for a water treatment products supplier and one of the elements of our products was air scour backwashing. In our products we used air at pressures as low as 60 psig (high volume) and in our pilot tests and R&D facility we used pressure up to 120 psig for the supplies.

We had a policy that no PVC piping was ever to be used for air transport, as it had been demonstrated (both at low pressure and high pressure) that when PVC piping ruptures, it fragments into sharp shrapnel, presenting a significant threat to safety. I wasn't present for it, but our R&D shop once had a PVC system rupture at 30 psig and it threw shrapnel all over the shop.

Other polymeric pipes (including PEX and, I think, ABS) form fishmouth ruptures that do not shatter, and are much safer for use with compressed air. I would never use PVC for compressed air.
 
Dan, this is incorrect.

We had a policy that no PVC piping was ever to be used for air transport, as it had been demonstrated (both at low pressure and high pressure) that when PVC piping ruptures, it fragments into sharp shrapnel, presenting a significant threat to safety.

That's fair, bad blanket statement on my part.

Hey, I plumbed mine in steel pipe.
 
That's fair, bad blanket statement on my part.

Hey, I plumbed mine in steel pipe.

Well, strictly, your statement was OK, because you said "use whatever you're comfortable with," but I thought it important to point out why people should NOT be comfortable with PVC in this application.
 
PVC BAD

OK having been in the industrial and construction world most of my life and having plumbed my own shop with PVC 35 years ago (Stupid)
Thought I'd save a buck.
I can tell you personally that PVC is a no NO no. I put PVC piping inside the walls and ceilings before insulating and closing up a 4,500 foot shop.
I have had to take the walls apart in three places because the fittings swell and blow apart.
The pipe has blown apart in two places in the barn that is part of the same building and I wasn't around to get hurt.
So that's 5 failures in 35 years. All preventable
I do not leave the system under pressure when I'm not working.
My three cents on iron pipe is I ain't going there ever again. To much leak potential.
As a millwright in a factory for two years 45 years ago and one of my biggest problems was air leaks from black iron piping threaded joints. Seemed like miles of it. And who ever built the system failed to put in any unions.
The company had just bought another 25 horse screw compressor because the existing 50 HP wouldn't keep up. After I fixed a few hundred leaks they were able to take it off line and the 50 now had room to spare and actually shut off now and then.
I won't use PVC BOOM, PEX (manufacture said it's not stable) or copper $$$$. BUT, I have found the new MAXLINE product to be superior to them all.
That is what I installed in my hangar. I feel it is a permanent system.
AS for water, I have an 80 gallon compressor outside in a small enclosure piped to another 120 gallon tanks inside ($100.00 Craigslist) I do not have any water in my airlines.
Giving the air a chance to cool allows the water to condense out and settle in either of the two tanks. Auto drains on both.
Oh for the giggles of it I bought an aircondenser to extract any left over moisture for painting.
I really like the Maxline system and yes it is expensive.
Oh the stories I could tell about air line problems.
Art
 
I've had black pipe similar to Dan's setup that runs uphill and several downdrops. If it leaks I should be really worried about my house gas lines, but have never had a leak in either. It seems (I couldn't say for sure) that black pipe is better at cooling but has the possibility of rust flaking off the inside. The drop lines are very useful and it's obvious the first drop removes most of the moisture in the system.
 
OK So I'll pipe in here about gas piping.
Comparing gas piping to an air system in a shop is way off base.
The gas piping in your house is at most -2- pounds pressure. Yes, I said 2 pounds of pressure. Unless you have large house with 6 or more gas appliances then they will jack it up to 3 pounds.
Quite a bit different than 175 pounds in my compressors air system.
Most in street gas mains are only 4-6 pounds and regulated at the house to 2 pounds.
Built houses for 43 years and have cut many a gas line with my shovel trying to find that little yellow pipe in the mud or dirt.
Heck the gas company has a running joke about me cause I plugged one by jamming in felt pen once. ON bang just dirt blown around a bit.
There is my experienced three cent worth.
Art
 
175# of air pressure will only happen if you have a two stage compressor. Looking at the compressor you will see a large and a small cylinder. If they are the same size, they are single stage and limited to about 125#. A single cylinder is a single stage and 125# max output.

Most shops will limit discharge pressure from the tank into piping to shop pressure 90# or a max of 125# psi.
 
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Consider Air brake tubing and fittings.

Consider air brake tubing and fittings. Available, easy and cheap and reliable. Heater tanks are a good idea for pressure stability at points of use. I use 1/2” and have no issues with pressure sags, the headers don’t need to be big. Two gallon HF specials are ok if you’re running a dryer. I would plumb half inch to a ball valve on a header tank, regulator to the connection. Your local truck distributor will have what you need. I personally (and professionally) prefer the Parker push to connect fittings. You want the DOT approved stuff, and CLEAN cuts on the tubing. Secure it every four feet, even zip ties with screw holes are fine. I ran a 60’ run from the back garage to my front garage and ran air tools with no problem when plumbed above. I fed my HVLP gun no problem ( although I needed a second compressor for long sessions)
 
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Isn't it a hoot how Dan can spark this passionate conversation that comes up periodically. Tip-up / slider, primer, shop air lines... He knew exactly what would transpire :). The distraction is welcome.
I think I'll enjoy my candies that arrived today from the greater VAF community.
 
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