Copper lines for compressed air

[Bill Leonard]

What is the difference between type L and type M copper for shop air, and which is preferred? I need to make a short run of about 20 feet with three air drops, Nothin' fancy.

[Chris Damm]

L is thicker and preferred for your application.

[Maury Saggus]

Unless you are running 1" line or over, or if you are running 175psi in the line, I would feel safe using either. Regulate the pressure going into the header, and you should be around 100-115psi in the header anyway.

Maury

[Bill Arnold]

Type M is not recommended for air line applications. Types L & K are recommended. I just finished running about 60' of 1/2" Type L copper to create three ports - wish I had done it sooner!

Edit: I posted the following in an earlier thread but will add them here. One of my drops is in my finish spray area so I have the following arrangement. I moved an HVLP regulator to the drop so I would have less bulk at the guns.
http://www.sawmillcreek.org/attachment.php?attachmentid=131098&d=1256588408

Two other drops are in my milling and assembly area and are like this:
http://www.sawmillcreek.org/attachment.php?attachmentid=131100&d=1256588430

In both cases, the pipe extension and valve allow moisture to accumulate and be expelled.

[Maury Saggus]

Type M is not recommended for air line applications. Types L & K are recommended.


Bill, I hate to disagree with you, but per the Copper Development Council's own Copper Tube Handbook, it states:
Compressed Air—Use copper
tube of Types K, L or M determined by
the rated internal working pressures as
shown in Table 3. Brazed joints are
recommended.
http://www.copper.org/publications/pub_list/pdf/copper_tube_handbook.pdfNow from the handbook, 1" Type M annealed tube working pressure at 250F temp is 326psi. This is not burst pressure, but working pressure. Burst pressures are almost 4000psi. Also, joint working pressure at 250F for silver solder is 270psi - less than the tubing working pressure. Brazing will increase the joint strength to over 320psi.

So, using 1" Type M and brazing will give 320psi working pressure at 250F.
Using Type L or K and silver solder will give 270psi working pressure at 250F.

In either case, the joint strength is much weaker than the working pressure of the tube.

I would rather use K if the price is right, but under 1", I have absolutely no problem with Type M, particularly in a home shop.

Regards,

Maury

[Bill Arnold]

Bill, I hate to disagree with you, but per the Copper Development Council's own Copper Tube Handbook, ...
In that same handbook, Table 1 shows in the Application column that Types K and L are recommended for Compressed Air whereas Type M is not.

:eek:

[Sam Layton]

Not to agree or disagree with anyone or any handbook...

Regardless of recommendations by any handbook, Type L is thicker, and in my book better. My complete house water, and shop air is plumbed with type L. Type L is not that much more expensive than M. The labor is the same. My commercial plumber friend said type K is mainly used in commercial applications.

Easy decision for me, thicker is better for me, type L all the way.

Sam

[Maury Saggus]

In that same handbook, Table 1 shows in the Application column that Types K and L are recommended for Compressed Air whereas Type M is not.

:eek:

Bill,

Type K & L are shown there because there working pressures are sufficient through all size ranges up through 10" tubing. We are talking about 1" and under tube here. That is why the quote in the manual I referred to earlier says Type M is acceptable, but refer to the internal working pressures on the charts.
Compressors to fill scuba equipment are rated to >5000 psi for compressed air. But you wouldn't use copper to pipe it because the working pressure of Type K tubing is not high enough, even though it says Type K is recommended for compressed air.

We can agree to disagree, but the fact remains that at 250F (typical air discharge temps at the head) 1" Type K with an Alloy E brazed joint has no higher working pressure than 1" Type K with the same brazed joint because the joint, not the tube, is the weakest link.

The only reason it would be necessary to go with Type L is it would resist impact better (less likely to bend). I prefer Type K, but that gets expensive...

Regards,

Maury

[JohnT Fitzgerald]

I don't know what K sells for...

at the local HD, L is anywhere from 35% (for 1/2") to 40% (for 3/4") more expensive than M.

[Bill Arnold]

I don't know what K sells for...

at the local HD, L is anywhere from 35% (for 1/2") to 40% (for 3/4") more expensive than M.
Type L costs more than M because it's stronger. What price is safety?

Some people swear by PVC and others talk about it exploding. PVC is cheaper than copper. :rolleyes:

Going with Type L for the 80' I put in recently was a no-brainer. I could have "saved" about $24 with Type M but safety won out over saving. ;)

[JohnT Fitzgerald]

Bill, I'm glad using L worked out for you. FWIW, I will probably also use L when I get around to plumbing my compressed air. However, I posted that fact because someone had stated that L is not that much more expensive than M. For small runs possibly, but for someone on a budget it might be meaningful.

[Maury Saggus]

Type L costs more than M because it's stronger. What price is safety?
Using a safety concern in this instance is a specious argument.


black iron is stronger
stainless steel is stronger/more expensive
nickel alloy pipe is tremendously strong/very expensive


Why would you not use these? What price is safety??

The reason to go to Type L or K here is not safety. It is aesthetics and reducing the likelihood to bend/deform the piping since Type M is softer.

To cloud your mind with safety concerns over Type M is disingenuous. They are all acceptable for typical home shop applications.

You will have to reason this for yourself. This is why I presented the data and the link for you to refer to in choosing for your needs. No one but you can determine the price of your safety.

Regards,

Maury