Ok, my opinion on some of the questions asked since my post...
Firstly, please visit this
Air Piping Layout for a diagram of a recommended compressed air plumbing strategy.
Why Type L (medium wall) versus Type M (thin wall) Copper?
The effective pressure rating for Type M copper will actually be approximately 400PSI rather than the 800PSI as Chis was inquiring. In the course of soldering -- especially for a beginner -- you are very likely to be annealing the copper line at the solder joints (particularly if using a MAPP gas torch vs. propane). Additionally, the line needs to be further derated because, during extremely heavy use, the air temperature towards the tank side of the line can reach 200-250F on air compressors without integral aftercoolers or refrigerated dryers. (NOTE: manufacturer recommended working pressures are further derated depending upon the type of solder used -- as little as 100PSI for certain types of Tin-Lead solder).
While Type M, even at 400PSI, is certainly greater than the 150-200PSI our compressors are likely to produce, I generally like to work with a 300% rating on pressurized systems. Additionally, I don't know if you have ever worked with Type M copper, but it is remarkably easily crushed and damaged compared to Type L. The thinner walls will also be subjected to a greater degree of expansion and contraction due to pressure fluctuations over the life of your install which will place greater stress on your solder joints -- so there is a greater risk of developing leaks at the various fittings with Type M (thin wall) copper versus Type L (medium wall).
Even with this strong preference for Type L, if I were choosing between PVC and Type M, I would choose Type M -- atleast you are not risking life and limb, so to speak, with the thin wall copper the way one would be with PVC.
Opinion on RapidAir (and the like)
I have nothing negative to say with regard to safety of the RapidAir setup. It is basically a reinforced flexible tubing system, so it does not have the same safety concerns as with rigid PVC piping. I do wish, however, that RapidAir had a greater working pressure rating as many air compressors are capable of exceeding the manufacturer's rated working pressure unless the compressor's pressure switch is adjusted to deliver a lower pressure. At least if their system fails you won't have the same dangers as associated with PVC -- just a compressor that's potentially left running 24x7 until the break is discovered (not a huge deal with 100% duty compressors, but a concern with compressors not rated at 100% duty cycle).
However, the
RapidAir tubing is typically used in professional installations which typically include a refrigerated dryer and, as such, deliver already dry air to the user.
Our typical shop setups do not tend to include refrigerated dryers, as such our systems
provide much wetter air. Part of the function of a copper or iron piping system (the longer the better) is to provide the hot incoming air time to cool down and transfer its heat to the metal piping. This causes excess moisture to condense in the metal pipes and, provided we draw our air of the top of those metal pipes, allows for the delivery of considerably drier air than we would have obtained straight from the air compressor's tank. It still will not be as dry as air provided by a refrigerated dryer, but it is much better than what you would obtain without the cooling provided by the metal piping.
The issue I have with respect to RapidAir (and comparable setups) is quite simple. The RapidAir piping has a much greater insulation value and far poorer thermal conductivity than that of either copper or iron piping. You will still benefit from some cooling within long runs with RapidAir piping, but nowhere near the same extent as with metal piping. It is also much more challenging to ensure a consistent slope with the more flexible RapidAir piping than with copper or iron piping.
Everywhere there is a dip in the RapidAir piping there is an opportunity for condensed water to accumulate. The only thing worse than an air tool spitting a little water is an air tool spitting LOTS of water -- remember RapidAir is usually installed in professional setups that include a refrigerated drier which means NO water condensing in the lines, so this is a matter of some concern to me.
Use of Mounted Air Hose for Distribution
See RapidAir comments above, they are largely similar concerns
Comments on Black Iron Pipe - a Possibly Cheaper Solution
If concerned about the price of copper (it is not cheap these days),
black iron piping is a traditional distribution system and is often cheaper than copper. Due to the rougher interior, use a minimum of 3/4" black iron for the main distribution line to reduce the losses in pressure and air speed. You will have to invest more time in a black iron pipe system since there are many fittings that must be well sealed with either
Teflon tape (use yellow Gas tape) or suitable pipe dope.
Install periodic unions throughout your black iron pipe setup so that if you are plagued with an unwanted air leak down the road you will not have to disassemble your entire distribution system just to tighten the troublesome connection.
Without unions the act of tightening one pipe connection invariable loosens the next connection -- with unions you just need to retighten all the joints within the affected section to correct the leak. Fixing a leak can still be a lot of work, but I would rather retighten or re-do 1/4 or 1/3 of my distribution system (up to the unions) than 100% of it!
Keep in mind, air leaks much more easily than water, so Teflon tape and/or pipe dope will be your best friend in this application. You can get by with traditional white Teflon tape, but you will need at least 3 times as many turns of the white Teflon tape versus the yellow Teflon tape to achieve the same result
Comments on Galvanized Piping
Although it looks nicer than black iron piping, many suggest avoiding Galvanized steel pipe due to zinc flaking off and plugging the air filters in coallescing filters. Personally, I'm not sure that this is really any worse than rust flakes from black iron pipe.
Either way, don't ever use a blower to clean up unless that blower is drawing air through a coallescing filter with either an integral fine paper or sintered brass air filter --
you do not want flakes of zinc or rust embedded under your skin!
Closing Comments
These are my opinions and are based upon extensive research I did when planning my setup. Ultimately, you will need to install whatever setup works for your shop and within your available budget.
The only *really* strong opinion I have is the avoidance of PVC distribution systems as they are just too unsafe. Woodworking can be a dangerous enough hobby with all our sharp hand and power tools without introducing homemade overhead IEDs into our shops!
HTH