Copper pipe for airline Question

[bdierks]

I see that most people are useing type "L" pipe. Can i use type "M"? Reason is i can get a bunch for free. ive been trying to find a psi rating for the type M and from what i have found so far, it seems like it would be fine. What do you all thinks????

Thanks, BRIAN

 

[Junkman]

Free is always good. I wouldn't use used copper pipe, but if it is new, then go for it.

 

[aac1431]

I used left-over (from plumbing the house) copper pipe (3/4") throughout my shop for air-supply. It has held up for two years now.

 

[the dude]

here is the copper pipe guide. It has all the info on using copper pipe for compressed air and what solder to use etc. Great resource that was posted up here before.

copper tube handbook

 

[bdierks]

What is the advantage to use 3/4" insted of 1/2"

 

[the dude]

volume and air flow

 

[mike944]

unless you're planning to run hundreds of feet, or hook up some huge sandblast machine, your flexable lines are going to be way more restrictive than the runs of 1/2" copper tubing. Yes, the 3/4 will give you less restriction, but you're always going to be limited at the single most-restrictive point in the whole system, and i'd be willing to bet it's not the tubing.

If you're getting it for free, you're damn lucky. Prices of copper are rediculous. Build the system out of watever you can get.

 

[Charles (in GA)]

Working pressures, annealed tubing, 150F degrees, type L
1/2"..... 613 psi
3/4"..... 495 psi

working pressures, drawn tubing, 150F, degrees, type L
1/2"..... 1242 psi
3/4"..... 1002 psi

Working pressures, annealed tubing, 150F degrees, type M
1/2"..... 420 psi
3/4"..... 346 psi

Working pressures, drawn tubing, 150F degrees, type M
1/2"..... 850 psi
3/4"..... 701 psi

Ref p.25-26 of the Copper Tube Handbook

Solder joint strengths at 150F degrees, up to 1" pipe.
50-50 tin-lead..... 150 psi
95-5 tin-antimony..... 625 psi

ref. p28 of the Copper Tube Handbook.

http://www.copper.org/resources/pub_list/pdf/copper_tube_handbook.pdf

Charles

 

[bdierks]

ya, im not going to be running anything near 420 psi. So i think it will be just fine.

MIKE944--- define huge sandblast Machine. I just built a cabinet that is 48wx30Dx30T. Thats actually the main reason i am going to be putting in the new lines. the cabinet is just to contain the sand. I actually have a presurized 20 gallon sandblaster that i will be useing.

Thoughts?

 

[1320stang]

I plan on getting a cabinet, but I'll be using the pressure pot as well. I'm going to run 3/4" hard L copper in my garage.

 

[fefarms]

An excellent article on compressed air piping design can be read here:
http://www.chemicalprocessing.com/articles/2005/12.html

To summarize: the critical criterion is air velocity in the main distribution line, not whatever point acts as the minium choke point. By keeping the air velocity at around 20 fps in the main line, water and dirt will be correctly captured by the drip legs, and won't be carried across them by high velocity air.

What this means is that 1/2 inch copper tube is good for about 11.7 SCFM max as a main line at a distribution pressure of 90 psi and a sea level shop. This corresponds to a velocity of 20 fps in the mainline. 3/4 inch copper tube gets you about 26 cfm under the same conditions

The absolute max suggested mainline velocity is 30 fps, which would mean 1/2 inch copper tube is good for 17.5 CFM. 3/4 inch copper tube is thus around 39 cfm

A pressure pot sandblaster with a small nozzle uses about 15 CFM steady state. As the nozzle wears the air use goes up. Main air tools such as impact wrenches use a great deal of air as they actually operate, but are rated at a more modest CFM, since there is an assumed (low) duty cycle.

1/2 inch copper pipe is fine for most drops, since drop velocity can go up to 50fps. But if you are going to all the trouble to hard pipe your shop I'd consider 1/2 inch too light for the mainline. I'd go with at least 3/4 for the mainline to get the best effectiveness out of the drip legs. Another advantage of bigger mainlines is that the air will be cooled more effectively at a lower velocity (a given parcel of air spends more time in the line).

A loop-style mainline could be used to stretch a slightly undersized main pipe into working, assuming the flow paths going around the loop each way to the most critical drops are roughly equal.

Type M is adequate for the pressures involved. Type L might be indicated if the line is subject to additional mechanical stresses like being whacked by objects or bent by opening/closing valves or attaching quick-connects.

 

[bdierks]

fefarms------ That information is fantastic. Thank you very much, very helpfull. now I think I pretty much understnad exactly what i need to do.

Thanks, BRIAN

 

[bdierks]

OK tell me what you think about this idea. I will get a piece of 3 inch steel or aluminum, mabey 3.5" round. it would be about 8 feet long. Cut it in half at an angle and weld it back together so it would sorta look like this,

. /-->
. /
. -->\
. \


HA, only one solid piece of course. So then, the the line from my compressor would go into the tube at about 1/3 up from the bottom. the outlet would be at the top, and thats where my copper tube would start. And there would be a drain valve at the bottom. So the idea is that a lot of the water gets condenced in the tube first before the copper lines. it fall to the buttom where it can be drained out.

My grandpa has a system like this, works pretty well. Whats your guy's thoughts?

 

[the dude]

Make it out of 2" black pipe and make it look like this... It seems to be highly recommended on a lot of welding/plasma forums for keeping water out of the system. Note, it "should" be installed between your pump and tank.

 

[bdierks]

Dang my ittle picture didnt come out right.. o well. But yes that is the same idea.

Why does it need to be installed between the pump and tank? how much of a differance would it make?

 

[the dude]

"They" recommend going between so that the trap collects as much water in the trap before entering the tank. Ideally you would have an intercooler in line before the water separator.

i think I read it on here somewhere, you want to:

Compress; Cool, Separate; Store; Use

 

[Morrisman]

Dang my ittle picture didnt come out right.. o well. But yes that is the same idea.

Why does it need to be installed between the pump and tank? how much of a differance would it make?

You need to cool the charge so the condensate drops out, and you need to slow it all down, hence the large 'seperator' pipe, so the droplets of condensate don't just get blown along with the airflow into the plumbing. You could also use your main air reservoir as a seperator, instead of the tube deal, and fit an automatic drain on the bottom, at the lowest point. Or even a manual drain if you can remember to dump it daily.

I work on huge air compressors (1500cfm, 2000psi) for my daily bread, and they have five stages of compression, with a huge water cooled seperator/cooler between each stage. We pull about a ton of condensate from each machine every day
Here's some of the plumbing on one machine. The big bottle thing on the right is the 1st stage condensate bottle:

 

[bdierks]

wow, what does all that air do?

 

[wantedabiggergarage]

I work on huge air compressors (1500cfm, 2000psi) for my daily bread, and they have five stages of compression, with a huge water cooled seperator/cooler between each stage. We pull about a ton of condensate from each machine every day
Here's some of the plumbing on one machine. The big bottle thing on the right is the 1st stage condensate bottle:

A ton of h2o? So what do you do with those about 239 gallons?

 

[SteveU]

What would the velocity be for 1" pipe? Read that article & tried to figure it out with their formula but did something wrong Does anyone know of a site that has a table with this information?

 

[fefarms]

It isn't that hard. Let me walk you through some examples:

From the formula:

V = 3 * q / (D*D)
Where: V = in feet per second
3 = approximate unit conversion constant
D = Diameter in inches
q = quantity of air being moved

The confusing part is "q". Compressed air is rated in SCFM, which is basically sea level temperature and pressure. But you are moving compressed air, which is a lower volume of a higher pressure gas. The document suggest
adjusting for q using a "compression ratio".

Compression ratio = Pout / Pin, where Pout and Pin are in PSI absolute (not PSI guage)

So, at Pout = 90 PSIG and Pin = 15 psia (sea level atmospheric)
We get Pout = 105 PSI absolute, Pin = 15 Psi absolue, so the compression ratio = 7.

So our formula becomes

V = 3 * SCFM / 7 / ( D * D)

Let's find velocity for 1 inch ID pipe and 40 SCFM of air at 90 PSI

V = 3 * (40 / 7) / (1 * 1)

V = 17 feet per second

Try it for 47 SCFM

V = 3 * (47 / 7) / (1 * 1)

V = 20 FPS

Or another example:

Suppose you distribute the air at 125 PSI, and you live in Denver (atmospheric pressure = 12.2 PSI), and you want to push 50 SCFM through 1 inch pipe

Compression ratio = (125 + 12.2) / 12.2 = 11

V = 3 * (50 / 11) / (1 * 1)

V = 13 fps

Let's now suppose that we use 1 inch "nominal" PEX tubing instead of copper pipe and the ID is 0.81 inches, other conditions the same as previous case

V = 3 * (50 / 11) / (.81 * .81)

V = 21 fps


As an aside I tend to be conservative on the compression ratio (preferring the 90 PSI numbers) to ensure suitable piping size as I approach the limits of the capability of my compressor.

 

[SteveU]

So running my 20 cfm compressor at an average of 130 psi thru 1" black pipe gives a velocity of 6 fps, looks like thats way below the 30 fps that they say will blow junk thru the lines I just tend toward overkill when it comes to sizing which in this case seems to be a good thing. This last summer I ran the compressor nonstop on a humid day for like 10 min with the air grinder then took a temp reading of the pipe, after the first 5' there was no measured temp rise & at the end there were only 2-3 very small water droplets in the separator. Would have liked to used 1" to 2" copper but the 1" was 57.00/ 10' stick & 2" was 14.00/ ft at the time

 

[fefarms]

Your math is correct.

I would make two adjustments.
1 inch black pipe is around 1.049 ID. Since this is an n-squared term it is worth considering.

I'd take the lowest operating pressure, not the average, since that is the point with the max velocity air. You mentioned the compressor running flat out for 10 minutes so it probably wasn't holding 130 psi.

So let's say the lowest pressure is 100 PSI.
This gives a compression ratio of 7.667

3 * (20 / 7.667) / (1.049 * 1.049) = 7 fps

Close enough to your figure of 6 fps -- your mainline pipe is plenty big enough.

 

[63Chevy]

Maybe I just missed it.

But what would be the difference going between copper or galvanized piping. The black pipe will rust so I know I dont wanna go that route. With copper being so expensive, I dont understand why alot of people choose this route.

Someone said they just liked the look. If that's the main advantage, it would be nice to know what the others would be...

 

[bmwpower]

Maybe I just missed it.

But what would be the difference going between copper or galvanized piping. The black pipe will rust so I know I dont wanna go that route. With copper being so expensive, I dont understand why alot of people choose this route.

Someone said they just liked the look. If that's the main advantage, it would be nice to know what the others would be...

Galvanized has a tendency to flake off, leaving particles in your lines.

 

[bdierks]

Galvanized can also rust. The "galvanized" part is gust a coating on the metal pipe.

 

[1320stang]

So if you came off the compressor head with copper to a section of 3" iron pipe that then went to the tank, that would be a decent aftercooler? It doesn't matter if it's galvanized or black, the air would slow down enough that anything should get into your tank. Plus you pour some gyptal into the iron pipe and drain it out, or send it off to be inside/outside powder coated so it'd look nice and perform well.

 

[Morrisman]

A ton of h2o? So what do you do with those about 239 gallons?

It all goes in the bilges, then through an oily water seperator and gets pumped over the side. There is a lot of oil emulsified in it from cylinder lubrication. Each machine ***** in 4 gallons of synthetic Rarus 827 oil every day.

The air is used to drive 'air guns', which make a huge bang underwater, bit like a glorified sonar, and we use that to map the ocean bed searching for oil and gas.

 

[Special55]

Maybe I just missed it.

But what would be the difference going between copper or galvanized piping. The black pipe will rust so I know I dont wanna go that route. With copper being so expensive, I dont understand why alot of people choose this route.

Someone said they just liked the look. If that's the main advantage, it would be nice to know what the others would be...

Just asking a question here so don't flame me.

How many people here have actually had their black/galv. pipe rust through in their home workshop application?

 

[malibu101]

Just asking a question here so don't flame me.

How many people here have actually had their black/galv. pipe rust through in their home workshop application?

Since you ask- 20 years ago when I lived at home I ran 1/2" galvanized pipe in my parents barn from my compressor on the 2nd floor to my work bay downstairs. Total run of pipe about only 50 feet. After I moved out dad put another compressor there and is still using my lines. On the end is a seperator with a clear bowl. Other than some smungy ugly water, which is why it's there, I have never even now seen any flakes or had a problem in any way.
FWIW- the lines have been under pressure since installed.
Does my experience make it right? No.
You asked and there it is

 

[tubeman]

I run 100' of galvanized with filters. I have inspected the filters several times and never seen any flakes.

 

[bmwpower]

What size filtration are you using?

 

[tubeman]

What size filtration are you using?

3 micron I believe... The filters are for paint spray guns.

 

[PAToyota]

Just asking a question here so don't flame me.

How many people here have actually had their black/galv. pipe rust through in their home workshop application?

It isn't as much an issue of rusting through as an issue of the rust and sludge getting blown through and clogging things up that are connected to the air supply...