Compressor and line question

[Julio Navarro]

I am thinking of installing some metal aircompressor lines. I want to use 3/8" metal tubing but I am not sure if that is large enough.

I want to use 3/8" mainly cos of price.

Is it better to go with 1/2" or even 3/4" or is 3/8" addaquate. I will be using it mainly for a brad nailer. Nothing really much larger.

[Jim Becker]

If you are talking copper, 3/8" is somewhat unusual, at least around here, and you don't get the extra storage and flow capability you'll have with 1/2". Personally, I think that 1/2" is the happy medium for this and it's readily available...including components like tees, corners, etc.

[Julio Navarro]

Thanks Jim.

I didnt mean copper as its pretty expensive. The steel gas line type is what I had in mind, not black pipe.

I can get 10' lengths at the borg for about $12 the copper line is much more.

I want to use 3/8" since the spiral hose seems to be rather narrow, certainly not 1/2". The 3/8" pipe is relatively affordable. But then as you pointed out there is the question of volumn, etc.

[Jim Becker]

Be careful of pressure ratings, Julio. NG or LP Gas is relatively low pressure. And remember we are talking about pressure for gasious use, not liquids. very different. Type L or Type K copper is certainly able to handle the job and many of us use it.

[David G Baker]

I like copper because of its pressure rating as well as its ease of use and availability. Yes copper is expensive at this time but depending on the distance you plan on running the air lines it may actually not that much more expensive than other pipe and fittings. I have all the tools necessary to thread metal pipe but most folks do not. If you plan on using metal pipe you should use the pipe rated for your intended use. I have read of guys using schedule 40 pvc pipe for their air lines but I would not due to potential hazards.
David B

[Al Willits]

Better idea may be 1/2 or 3/4" black pipe, Graingers has it for about $23 and $20 for 10' sections.
Probably cheaper if you look around.
Much stronger and pipe fittings are fairly easy to work with.
1/2" should give you enough capacity for most useages.

Al

[Carroll Courtney]

I ran mine in 3/4 pvc schedule 40 pipe.I have an 80gal 175 psi compressor for about the last 10yrs w/no leaks and no pipes have burst.I install drip legs where ever I made a drop w/drain valves. If you ever use a hvlp air sprayer,you will need the cfm's.I got the idea from a tire shop that ran all their air lines in pvc pipe. Its cheap and fast! Carroll in Porter Tx

[Frank Chaffee]

Julio,
You don’t state the length of the run of pipe, but one thing to consider is the effect that resistance through piping and connectors has on flow rate. I would do the shop piping in at least ½” dia. and use 3/8” hose only to the tool.

[Kyle Bowers]

My compressor is in one corner of my 12' X 24' shop. I have 3/4" pvc running both directions to the far corner of the shop and cut off valves for both runs at the compressor so I can isolate one branch if needed. I have short 3/8" short nylon tubing on each of my tools with quick connects for adding extension hoses if needed. I also have a 3/8" remote drain valve and line leading outside so I don't have to lay down to drain the compressor.

The only failures I have had were bad joints I made when I glued the connections.

[Jim Becker]

I ran mine in 3/4 pvc schedule 40 pipe.I have an 80gal 175 psi compressor for about the last 10yrs w/no leaks and no pipes have burst.I install drip legs where ever I made a drop w/drain valves. If you ever use a hvlp air sprayer,you will need the cfm's.I got the idea from a tire shop that ran all their air lines in pvc pipe. Its cheap and fast! Carroll in Porter Tx

And dangerious. The problem is that PVC gets brittle and is not rated for compressed gasses. Should it burst, shards could cause personal physical harm. And that tire shop is in violation of OSHA rules to the best of my knoweldge... ;)

[Ed Costello]

Hello,

I am not sure I know anything about the pipe that you are thinking of using. I build environmental remediation treatment systems. I deal with all sorts of pipe. Black iron, copper, fiberglass, h.d.p.e. and plastic. Experience helps with all materials but plastic is by far the simplest to use. I have put together tens of thousands of feet of plastic pipe. Most of it handling air. I would suggest copper first, but if budget is the issue I would use shedule 80 pvc. Very easy to put together. Fittings and hangers are much cheaper. Just remember to hang it up out of the way. (protected from traffic, lumber etc.) Use plenty of hangers to secure it. "J" hooks for horizontal overhead runs. Split rings, threaded rod, and deck plates for drops. Follow the directions on the cans of primer and solvent cement exactly. The main line in my work shop is 3/4 inch and I spur off with 1/2 inch drops. 3/8 inch regulators and separators with 3/8 hose on every one. Spend money on HOSE and quick disconnects or you will be sorry. Low quality hose is a nightmare. You can go to the Spears website to see all the pvc fittings available. Good luck!!!!

[Greg Funk]

I'd read this: http://www.osha.gov/dts/hib/hib_data/hib19880520.html before running compressed air through exposed PVC pipe. It hardly seems worth the risk.

Greg

[Ed Costello]

Try this link. Hard to figure out who to trust.


http://www.engineeringtoolbox.com/pvc-cpvc-pipes-pressures-d_796.html

[Jim Becker]

Ed that page doesn't indicate if it's for liquids or gasses...and I suspect it's for liquids. Liquids don't compress. Gasses do. Different animals.

[Ed Costello]

:eek: :eek: :eek:


Jim,

You are right and I was wrong. After further investigation I found this link.

TECH-2-No.106 (http://www.sawmillcreek.org/TECH-2-No.106)

All pressure ratings I found must be for liquids. The systems I install are high volume and low pressure. (about 40 psi max) I am glad the piping in my shop is copper!!!!!!

[Ed Costello]

Sorry..............bad link. Try this


http://www.spears.com/tech_updates.htm


then click on: TECH-2-No.106 (http://www.spears.com/tech_updates/Tech-2-No.106_web.pdf) Understanding Molded Pipe Fitting "Pressure Ratings"

[Steve Kohn]

I would suggest that people do the math. I went thru the calculations of PVC versus copper for my hobbiest system about 6 months ago. The total difference was about $150 (with copper being the more expensive option). I have thousands of dollars invested in my shop, and the difference in price on a compressed air system didn't seem to be worth the risk of putting in a PVC system that every safety agency is recommending against.

Is it really worth the risk?

[Randal Stevenson]

There are two types of plastic airlines that are approved for air compressor use, otherwise, it was like a $10,000 fine in a commercial application. The first one is made of ABS (duratec, I think), and colored differently then plumbing ABS. The second one is a pex composite (PEX_AL_PEX, from memory).
In the shop I have access to (auto), the lines are a conglomeration of black iron, galvanized (mostly fittings), and some copper, as things have been changed several times in the 50 years it's been around.

You never said what type of pipe your were talking about (I assumed galvanized), but consider this; your airlines are a spare tank, for a brad nailer/finish nailer, 1/2" is fine. Once you move up to something like spraying, I would consider 3/4 and make sure your compressor exceeds the volume required specs.

My $.02

[Rich Engelhardt]

Hello,

I have a dumb question.

Other than being more resistant to possible damage, is there any other advantage rigid pipe has over using just regular air hose?:confused:

[Kurt Strandberg]

Be careful of pressure ratings, Julio. NG or LP Gas is relatively low pressure. And remember we are talking about pressure for gasious use, not liquids. very different. Type L or Type K copper is certainly able to handle the job and many of us use it.

Is 100 psi of air the same as 100 psi of water in a steel pipe system?

[Jim Becker]

Is 100 psi of air the same as 100 psi of water in a steel pipe system?

I am not an engineer, but it's been indicated a number of times over the years by folks more knowledgeable that the fact that gasses compress puts a different twist on things. (Consider the volume of air that can be put in a scuba tank, for example. Another one might be how the ballast tanks on a submarine operate) So in your example, there is more air in the equal pipe than there would be water at the "same" pressure and this is likely why the testing/rating needs to be different.

I'd rather err to the conservative on something like this, personally!

[Jim Becker]

Sorry..............bad link. Try this


http://www.spears.com/tech_updates.htm


then click on: TECH-2-No.106 (http://www.spears.com/tech_updates/Tech-2-No.106_web.pdf) Understanding Molded Pipe Fitting "Pressure Ratings"


You'll note that there is a nice warning at the bottom of the document, "Not for use with compressed air or gas"

[Mike Chrest]

I am not an engineer, but it's been indicated a number of times over the years by folks more knowledgeable that the fact that gasses compress puts a different twist on things. (Consider the volume of air that can be put in a scuba tank, for example. Another one might be how the ballast tanks on a submarine operate) So in your example, there is more air in the equal pipe than there would be water at the "same" pressure and this is likely why the testing/rating needs to be different.

I'd rather err to the conservative on something like this, personally!


Jim,
What you are trying to discribe is potential energy. The pressures are the same but the scuba tank has more potential energy than a tank full of water at 100psi. The scuba tank is a potential bomb because when the compressed air uncompresses the volume it occupies is significantly greater than the volume the compressed water would occupy(water compresses very little). The air acts as a propellant for any shards of plastic from the broken pipe.
The metal pipe is much stronger than the plastic so you have a larger margin of safty with metal pipe. But if you over pressurized the metal pipe or tank with air it would explode the same way.
Mike

[Randal Stevenson]

Hello,

I have a dumb question.

Other than being more resistant to possible damage, is there any other advantage rigid pipe has over using just regular air hose?:confused:

Yes. First you really need to look at what your using it for.
It allows better moisture seperation (not as important brad nailling as compared to painting). Available in bigger sizes (acts as a spare tank), and you tend to figure out where you need it and the runs tend to be shorter (ever drag out a 50' hose when you needed 5").

[Ed Costello]

Yup. Thats why I posted the link. Had a hard time finding that warning. Kinda had to dig through quite a few sites to find what not to put through pvc pipe.

[Kurt Strandberg]

I am not an engineer, but it's been indicated a number of times over the years by folks more knowledgeable that the fact that gasses compress puts a different twist on things. (Consider the volume of air that can be put in a scuba tank, for example. Another one might be how the ballast tanks on a submarine operate) So in your example, there is more air in the equal pipe than there would be water at the "same" pressure and this is likely why the testing/rating needs to be different.

I'd rather err to the conservative on something like this, personally!

The reason I ask is I am a Sprinkler Fitter (fire sprinklers) and we install wet and dry systems, the dry system has a dry valve with a clapper to hold back the water untill a air loss, (fire or damaged head) the clapper is sized to the pipe on the wet side (2", 4", 6" usually) and the air side of the clapper is bigger so the maker says usually a 5 to 1 or 6 to 1 ratio, so the valve will trip at about 12 psi of air for about 70 -75 psi of water.

Most of my coworkers say that 40 psi of air is the same as 200 psi of water or 20 psi of air = 100 psi water and so on, I say if that is true why isn't the clapper the same size on both sides in the dry valve?


Sorry for the off topic long winded rambling

[Carroll Courtney]

Guys, pressure is pressure reguardless if it is a liquid or gas.Depending on what gas (not air) it is.Gas such as freon(what I work with) will expand and contract w/ temp and pressure.If a pipe such as PVC has a psi rating of 250,then it will work for what-ever, as long as you don't go over the rating.As for the brittle of plastic pipe,most are not UV rated,so don't expose it to the sun.Pipe will split before it will burst if you exceed the rating. Far as the tank goes, exp. your putting 5lbs of air into a 1lb container."That's all I got to say about that" If my pockets were deep,I would run it in the 3/4" black pipe,taking into account the cutting,threading,and fittings into the cost.This has turned into a debate.This why I like the SMC forum,where you can exchange ideals with safety being a priority.I feel safe around my pvc pipe w/ 150psi on it for the last 10yrs.Chemicals run through it at work going into cooling towers for water treatment.When all else fails,use common sense.

[Mike Chrest]

Schedule 40-3/4" PVC pipe has a joint strength(solvent weld) of 288psi. Threaded joint is 240psi. Recommended safty factor for compressed air systems is 2.

(240psi/150psi=1.6 safty factor)

Safty factor for water systems is 1.25.

If you keep the pressure in the system below 120psi and it is not exposed to sunlight you can get away with it. But why take the chance? Copper tube(1/8"-1") working pressure is 1095psi with 95-5 solder.
Mike Chrest
BSME U of I '80

PS: If you just "have" to go with PVC use female threaded quick disconnects so the PVC fitting is a male and will be under compression.
Don't count on the pipe always splitting instead of bursting. Consider how a pipe-bomb works. This is why the safty factor is higher.