I am planning to build out my basement workshop. I am thinking it would be nice to have a little run of compressed air piping to go around the shop and also near the window by the driveway for outdoor use. Even considering running up through a pipe chase with some connections on each floor of the house and in the attic. Not that I would use these all that frequently, but I am going to be doing some work in there anyway, so what the hell, right? Figured it would be easier than dragging hoses all around, since my compressor isn’t all that portable.
I was thinking of doing it in 1/2″ copper – I’ve seen compressed air in copper and black iron pipe before. 1/2″ should be sufficient and would have less pressure drop than hose. At the lengths I am talking and at 2 or 3 times the output of my compressor, I am still OK from a pressure drop standpoint.
However, due to some research (very important scientific research) on construction of pneumatic potato cannons a few years back, I remember that 3″ sch 40 PVC is rated at 330 psi or something like that, and 1 1/2″ is rated at like 600 psi. Since PVC is easier to work with than Cu, and also cheaper for a much larger pipe diameter, I figured I could reduce pressure drop at the same time as gaining some additional storage volume in my system.
Any reason I cannot use regular sch 40 PVC for compressed air at 100 psi? Is gray ABS better?
Thanks.
p.s. if anyone has any questions about pneumatic potato cannon, ask me, it’s a really cool design.
Replies
Exposed plastic pipe for compressed air is not a good idea.
If it is impacted while under pressure you will have an explosion. The shrapnel from the plastic can be deadly. At the very least injuries to oneself.
At least with copper it will bend. Go to the trouble of doing the exposed pipe in copper or black pipe. If copper use the thick wall stuff.
Here at work all large supply pipes are in black pipe. Only the short runs along the work benches are in copper.
If at first you don't succeed...try again! After that quit! No sense being a dam fool about it! W.C.Fields
I'm with Jet on this one. Use black pipe or heavy gauge copper and don't forget the in-line filters and water traps.
Kevin Halliburton
"One machine can do the work of fifty ordinary men. No machine can do the work of one extraordinary man." -Elbert Hubbard-
Speeking of water traps.
At work we have water purge valves. they are located at the lowest part of the pipe and let out some air every few seconds. Like a slow ticking clock. As the hangers for the airplanes are beyond big,it would be impossible for the building maintce, people to get to all the drains each month.
We use to get all kinds of water in our tools each summer. Since they installed the automatic water purgers I've never seen water in the lines.
Don't know the manufacturer of them.
If at first you don't succeed...try again! After that quit! No sense being a dam fool about it! W.C.Fields
Thanks for the caution on pvc pipe. I knew it wasn't recommended practice, but wanted to see what the reasons were. I thought maybe something to do with thermal expansion rate, or maybe fatigue due to pulsating pressure.
On those timer-controlled drains:
Timer controlled drains use less energy than leaving a valve cracked open, but... you can save a lot of energy if you install zero-loss drains instead. Rather than purging for a fixed duration at fixed intervals, they only purge when they have collected a quantity of water, and then they stop purging before letting any compressed air escape.
Should also probably have drains at your storage tank and air dryer, and aftercooler, if you don't already have 'em.
Alec
Our compressed air on the lot is all in copper, and in most locations it's not used very often. Water purge valves are all manual, you open one and blow out the water when you need to use air in a particular area.
-- J.S.
Check out the last Tools & Shops (issue 160) of Fine Woodworking. There was an article about plumping a shop for air. I'd guess it's still available at newstands, don't know for sure. Or click this link to get back issues.
http://www.taunton.com/store/pages/backissue_fw.asp
Author chose black iron pipe, 3/4" for main runs and 1/2" for shorter drops. Didn't choose copper because of fire hazard involved in sweating it. Specifically says not to use plastic due to explosion hazards mentioned above.
If everything seems to be going well, you've obviously overlooked something.
Ditto on the exploding plastic pipe thing. Particularly if it's cold. Plastic is much less impact resistant at lower temperatures.
When my company built a new shop, 1000's of feet of air piping, they used plastic for piping ran up above the ceiling to save money. But, all exposed pipe is copper. Saved a lot of money because of the quantity used, and it was easier to glue plastic pipe in awkward spaces, but it's contained even if it bursts. Not sure it met code, but that's how it was done.
Me, when I run airlines, I'll eat the cost and put in copper pipe. Long term, it's a better way to go.
Oh, we also put valves on all drops. Some quick disconnect fittings leak. If you turn them off when not in use you eliminate this problem.
I think everyone set you straight on the material issue, but what's this about having lines in the house?
How often do you really need an airline in the living room or bed room? Bring the compressor in when you're working and remove it when done. Or, perhaps you can just run a long hose though the house when needed?
I see this as a potential safety hazard especially if there are kids around.
Sounds like just the thing for blowing dust bunnies out from under the beds.
I am in agreement with those that have stated that PVC pipe is dangerous for compressed air. When compromised, it demonstrates brittle failure - ie. flying, jagged pieces.
However, little over a decade ago, while working in the salt mines (seriously) I had to supply compressed air into the mine. In this extremely corrosive environment, one has two options 316 stainless steel or plastic. There was a company supplying ABS plastic for compressed air applications. It was paramount that it was Schedule 80 and to avoid the customer from inadvertantly using Schedule 40 pipe, everything was sized to metric specifications. You had to have the proper pipe from them for everything to fit together. Needless to say, way, way cheaper than stainless steel. Please take note this was ABS pipe and NOT PVC,; ABS fails in a ductile manner.
Several years ago I wanted to run some compressed air pipe through a wet environment and this company came to mind. I contacted them, however, they no longer carried said product. In fact, one is hard pressed to find very much ABS piping used in the U.S., other than DWV. On of the problems is that ABS is very sensitive to UV degredation and suppliers would order it, leave it sit in the sun in their supply yards, and the customer would end up with an inferior product. I imagine the manufacturer always heard about it one way or the other.
Any way; a little side line story - don't let it subtract from the good advice provide here by others.
Edited 4/18/2003 5:10:33 PM ET by ADGUSTUM
Edited 4/18/2003 5:13:24 PM ET by ADGUSTUM
Edited 4/18/2003 5:14:29 PM ET by ADGUSTUM
I didn't see an option to attach a file in the edit mode. Hope this file is clear enough.
One of the reasons you use metal pipe is because is encourages the condensing of water. Black or galvanized pipe has more surface area for a given length compared to copper, so it probably does a better job for a given length run. Picture the hard metal lines in your air distribution system like the coil of a still and you get the idea.
This is also why you want them to slope downhill towards a water collection trap at the end of the system, so that the flowing air carries the condensed moisture with it. Also, because water will always be at the bottom of the pipe, you have to tap off for air vertically as was illustrated in the FWW #160 article.
Jon.
Edited 4/18/2003 5:26:00 PM ET by WorkshopJon
Upon rereading, I see Jet mentioned something about purge valves. One trick I've been doing for years is to have all the drain valves in my system, including the one on the compressor tank, open just a tad always. Just enough to allow water to weep out. There is almost never any water ever in the system.
Edited 4/18/2003 5:35:01 PM ET by WorkshopJon
Edited 4/18/2003 5:35:33 PM ET by WorkshopJon
What size compressor do you have, how many valves do you have cracked open?
Sounds like you'd use a lot of extra compressor energy to be purging all the time.
Alecs,
To answer your questions:
7.5 hp two stage 80 gal. 175psi.
About 100' of piping.
6 drain valves including tank.
Cycles about once a day if I don't use it, Undoubtedly @2:00am.
I don't keep the valves cracked open per say, just open enough to barely here a very, very, very slight hiss if my ear is ~2" away.
Jon
Definitely not PVC as everyone has said, for the nasty failure mode. Not jsut from taking a hit or getting cold. But also if you get some that has sat outside for a while. It gets UV-embrittled. Before acceptting a large order of PVC, I always pressure-cut a few test pieces. Maybe 1 in 30 or 1 in 50 loads, I refuse. And I try to order from suppliers that I know store their stock inside.
Note for while PVC, carboard shipping tubes and every other dang thing has been used in potato cannons, exhaust pipe 2" (or 4" in a truck shop) is lightwieght but without the brittleness of PVC.
David Thomas Overlooking Cook Inlet in Kenai, Alaska
Go with copper unless you will be using the air every day.
Made the mistake of putting 1/2" black iron in own shop, house, and garage about 25 years ago. Gets used only once or twice a week and often can be not used for a month or so. Anyway, after about 15 years, there were leaks in the QC fittings due to some flakes of rust - you never can get all the water out. As others have said, if used everyday with automatic purges, condensation is more controllable and black iron would work well. Some of the big setups have a mechanical refrigeration deh;umidifier on the systems, a little past home expense rationale.
"Go with copper unless you will be using the air every day."
Just curious. Why do you think corrosion would be greater if you use the air less often. What am I missing here? ie. with heavy use, more water passes through the system, causing more corrosion.
Jon
Edited 4/19/2003 9:14:24 AM ET by WorkshopJon
alecs,
I plumbed my air system from the garage and into the house using 3/4 copper with isolations and drains at all the drops. My compressor (6 HP) is in the garage, though my shop is in the basement. The transition was going to be a pain, snaking pipe and sweating through the sill, till I thought of hydraulic hose. Bought a short length of 3000 psi hose and snaked it through, connecting via hydraulic and copper fittings; works great.
Sidelight, I use the air in my shop more than in the garage, but I had the electrician set up switches in both the garage and basement so I could turn on/off the compressor without leaving the shop. Works through a relay and switched via 28volt LV wiring.
The other bennie to the compressor being outside, is the noise is not nearly as bad. I also leave the tank petcock open a tad, allowing drainage.
Good luck.