Another Air LIne Plumbing Question

As a mechanical contractor, I see every type of piping system used for compressed air. Copper is one of the best - clean but now very costly. Threaded galvanized or black iron work well and cost less - but require threading.

Do not use pvc piping for compressed air systems. PVC piping will shatter upon impact - creating dangerous shrapnell. Synthetic oil also causes pvc piping to embrittle and break. There are specialty plastic and poly piping systems for compressed air- but are fairly expensive. PVC is an attractive product, since it is cheap and easy to install. Be wise and use pvc only for process water or drain applications.

1. I assume you put in some vertical T"s to act as water knockouts? How many did you use? What do they look like?

2. Do you have to worry about pitching the pipe?

3. Do you leave the system always pressurized?

4. I know the size tube depends upon the capacity of air tools you want to run, but also the smaller the tube the higher it"s pressure rating. What size did you find practical?

5. Did you just use quick disconnects on the terminals, or with valves as well.

Any other suggestions and recommendations would be appreciated! Thanks

There are many different ways to set up a compressed air system and CNKS has linked to one good one for you. However that one may be more complex than what you need in order to serve your purposes. I take it that you are planning on having compressed air available on two levels, one above the other. Is your compressor (with tank) going to be located on the first level? How large are the work areas on each level? How many air stations on each level do you think you really need? It's common for home shops with limited air capacity and single users to overbuild considerably, based on typical layouts for commercial operations with large capacities and multiple users over large shop areas. You should minimize the total number of stations because they can get expensive. My shop is small at about 24ftx24ft on one level. I need only a single station for any of my work and it is located next to my compressor. This simplifies things considerably. I can reach any area in my shop with a single length of hose from that station.You can see what my single station looks like by clicking on the thumbnail:

If I were to add air to the level above, I'd add the upper station directly (more or less) over the one on the first level to minimize and simplify the piping runs. I use a two-stage compressor (17 cfm capacity at 175 psig) with an 80 gallon tank, don't have a moisture problem to speak of and don't need long runs of metallic piping for any kind of moisture control. Unless you have unusually large air demands for a home shop with a single user at a time, I doubt you would need to go to 3/4" for any of your piping, especially if it is not extensive. If I were to add another station on the level above the one I have, I'd only go with 1/2" to feed it. Tell me a little more about your compressor, it's capacity, the areas on both levels, the number of stations you need on each level and your estimated peak air consumption at the station farthest from the compressor. I'll give you my opinion on how I'd go about it.

I always leave my tank pressurized. I see no valid reason to drain it down after each use, even if I have no planned use for days or weeks. I do have a minor leak in between one of those filters so I do shut off the air to the station to prevent the tank from draining down and the compressor starting. Sometime I will try to fix that. It's one of those issues with a threaded connection in an aluminum or pot metal housing where I am concerned that another turn around could crack the housing. A reason why I hate threaded joints - at least those with taper pipe threads w/o the o-ring seal.

Don't use quick connects anywhere except at your station connection(s) and downstream from there. Even then, you should minimize their use. In other words, don't have a lot of short hose lengths connected together with quick couplers to make up a long one. There are different knids of quick connects, some with auto shutoff on disconnect and others with no internal valve. Mine are all the auto shutoff type so I don't need a separate station shutoff valve. I do all my painting outside and also do other work outside that uses compressed air. I'd consider an outside connection as completely unnecessary. I have no problem extending hose outside when I need to. My single air station is only about 10 ft from the garage door. Every installation is different and doing some custom planning up front can avoid unnecessary work and expense.

Rod

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Hi Rod

Thanks for your reply and offer to help suggest a design. My air volume requirements are pretty low, as I paint with a HVLP turbine system and only use air for nail guns, blow off, air wrenches, etc. My shop is a 30x40 foot bank barn (2 story) I’ve converted into a workshop (woodworking upstairs, mechanical downstairs). Currently I a use a 2 HP Sears compressor: It’s capacity is approx 12 CFM @ 90 psig, and it runs at 100 psig. I just purchased a 30 gal vertical tank from Grainger after the original Sears developed a pinhole leak (alas due to infrequent draining) and was subsequently tossed out. This is a good time to build a good manifold Along with the old tank I junked the old controls and will purchase a new pressure switch. I have an external regulator and KO filter I’ll continue to use. Perhaps I should look into some of the other components you show in your station. Someday I’ll upgrade to a larger compressor but it is sufficient for my needs at the moment. The compressor will be mounted on the ground level.

This is the first time the lower level’s been put into use, after pouring a concrete floor this Fall. Setting up for air availability on both levels in a central location would be a welcome convenience. For now a single delivery station on each level would be fine. Air hoses can take it from there. I could always extend them as needed in the future.

I anticipate locating the compressor in an out of way corner on the lower level, next to a sump (may be a good reminder to drain it more regularly this time). I was anticipating bolting the tank to a couple short lengths of 6x6 timbers rather than anchoring it to the floor. As this thread recommends I’ll purchase a 36 inch flexible hose for tie in to the rigid piping.

The air line would leave the compressor and pass vertically to the ceiling, turn 6 feet over, and then again turn 90 degrees to traverse 15 feet across the upper level floor joists to a central wooden post, from there branching upward 5 feet thru the floor to the upper level station, and downward 10 feet to the lower level station. It seems like the lower level would act as a water knockout so perhaps I should provide a vertical branch right above the lower delivery point to allow any water to bypass the delivery. (Barn is unheated and in New Jersey)

Would you recommend the equipment your photo shows (filter, knock out, regulator) at both levels, or just one at the compressor? Sounds like 1/2 inch Type L copper would be your recommendation. I"d appreciate any suggestions from your experience.

Once again thanks for your help!

Paul

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Here"s a view directly above. Upstairs air station would be mounted at the vertical 4x4 post.

I think your idea of the 6x6 beams under the compressor is a good one. If I understand your planned arrangement correctly, I would pipe it up as shown here (pdf file). I have shown some 3/4" copper because your single stage compressor is operating at a lower pressure than a two stage and therefore you do not have the larger reserve margin for pressure drop between the storage tank and the stations. If you were starting out with a two stage machine running 145-175 psig, I'd stay with 1/2" all the way. I am sure 1/2" would work in your case also, but I think the 3/4" would be a more prudent choice in the area where I indicate.

I also recommend a separate drop (in addition to the station drop) from the header in the ceiling area of the lower level for a dedicated water drip for the main header instead of combining it with the station drop. The valves shown for draining purposes don't have to be full sized valves. They only need to be "radiator style" petcocks. The isolation valves should be line-sized, preferably ball valves. You can add in the 8" riser sections at each station as shown on that TPTools diagram if you wish. That's a refinement that is probably not necessary but does no harm and could help some. If you have the fittings, go for it.

Since you are using a single stage compressor, moisture issues will be a greator concern that they would be with a cooler- running two stage. For that reason you might want to consider using a 10' or so section of copper fin-tube in that 15' run along the lower level ceiling. That's the same stuff used for baseboard hot water heating systems and would help promote better heat transfer and condensation. The reason that I suggest this area for the fin-tube is that the fins are aluminim and are easily damaged. If you can protect the fins w/o obstructing them, locate any fin-tube in that riser section immediately after the compressor instead of in the overhead. The closer to the compressor, the better.

Yes, I would stay with type L copper throughout with the possible exception of any fin-tube. I am not sure if that is available in L - maybe only M. If it's available in L use that, otherwise M is OK.

The filter arrangement I show for my single station is likely overkill. I set it up conservatively for the most demanding use, which is painting, although it gets used for everything. Most would find a combination separator/filter/regulator unit, such as that sold by Sharp and others, quite satisfactory, even for painting. I strongly recommend locating separators, filters and regulators at each station and not trying to do those functions on a global basis by installing a single set back at the compressor. You want to run the header and distribution piping at the highest pressure available (tank pressure) for more efficient condensation of moisture. The line dewpoint increases with pressure and it is easier to condense out moisture if the line pressure is high. Pressure drops are also less for the same flow if the line pressure is higher.

One thing to remember if you are going to purchase additional filters/separators/regulators. They do not have to be line-sized. It's probably better if they are not since line-sized equipment like that usually winds up to be significantly oversized in capacity, which is not always desirable. It's the rated capacity that counts, not the size of the connections. For a 1/2" nominal station, such connections may be 3/8" or even 1/4", depending on the equipment details concerning capacity (in cfm).

Take this as suggestions for consideration. Modify as you wish. Good luck with it.

Rod

Thanks so much for your suggestions and design. You brought up many issues that I would not have thought of, particularly the impact of single stage vs double stage compression, and operating pressure, upon water content and removal. I like the finned tube concept. I"ll certainly follow your suggestions when I build the system in another couple of months.

Paul

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Also do you guys mount your lines right up againest the wall?..... ..... ...Todd

Yes, you should be concerned with vibration and possibly even some creep or "walking" of the compressor tank out of the initial position. I use a rubber hose connection between the storage tank and permanent wall piping. A prior post giving the details of my installation is here. My tank is an 80gal vertical and does have a tendency to do some minor "walking" on a concrete floor over time. One of these days I will put some machinery "feet" under it to prevent that but the hose should be used anyway, just from a vibration standpoint. If you do any plumbing or re-plumbing between the actual compressor pump and the storage tank, do NOT use standard solder connections in copper. The joint pressure rating will not be high enough at the temperatures involved at that location. That's why you always see mechanical joints when copper is used there. Copper (with standard soft solder joints) is a fine choice for the wall distribution piping downstream of the storage tank however. I'd recommend the 95-5 Tin-Antimony solder rather than the 50-50 Tin-Lead. Joints made up with 50-50 could be marginal, pressure-temperature wise, especially if used adjacent to single stage compressor units with small tanks.

Rod

Get a set of pipe brushes and brush the heck out of your fittings and pipe. Use plenty of flux and you'll have no problems.

Copper pipe is out of sight right now, though. I haven't compared it to black pipe lately, but it's got to be close in price.

Being from the old school, I'd not bother with anything "pre-applied", including solder in joints. Matter of fact, I can't say I have heard of such things. I recall seeing some copper fittings once that had a pre-installed ring of solder in them. I think they had a "bump" around the OD to provide a recess on the ID for a pre-inserted solder ring. Maybe that's what you are referring to. With those, I guess you'd just add heat. That seems to me to cost more than is necessary. It would also seem to down play the very real need for good cleaning and fluxing of all surfaces in the joint. Cleaning (deoxidizing) of even brand new copper tube and fittings is one of the keys to successful solder joints. Anything that does not emphasize that by implying a "just slip it together and add heat" scenario as a quick fix is not the right way to go about it in my opinion. Besides, I think you should learn to do it using a roll of solid core string solder. It's really not hard. Making sure the surfaces are completely dry, have been fully cleaned and fluxed is the most important. The part that needs to be learned by practice is exactly where, when and how to apply heat to the joint. It shouldn't take long but might require a few joints to get the hang of it. I'd recommend you start with 50-50 tin-lead solder because that is easiest since it has a broader band of semi-liquidity (is that word?) between solid and liquid. It's a little more forgiving for the beginner. Actually, all my compressed air work has been with 50-50, even though I generally recommend 95-5 to others. I know the area close to my storage tank is always cool enough to be within the pressure-temperature rating of the joints. I don't know that to be true for the installations of others. You may have some trouble finding the 50-50 in some places since it no longer complies with code for potable drinking water service because of the lead content. Ask for it if you don't see it displayed.

The very best information on copper tubing, pressure ratings of tube and fittings, P-T ratings of joints with different solders, how-to info, etc is the Copper Tube Handbook published by the Copper Development Association. You can download a free copy of the 6+MB pdf file here. Save it to your hard drive and read it from there. You'll refer back to it over and over. It's all you ever need to know about the proper use of copper tubing and fittings. The tubing comes in three basic wall thicknesses - type K, type L and type M. Type M is the thinnest and least expensive but still has plenty of pressure capability for normal shop air sytems. I like to stick with type L for general purpose use though, simply because (by having a thicker wall) it has better resistance to physical abuse than type M.

You probably will find it is expensive. I haven't bought any recently. I'd start at places like Home Depot unless you can work a trade discount at a plumbing supply wholesaler - or know somebody who can. I've found Home Depot carries NIBCO tube and fittings. NIBCO is a well know brand name for all things copper and has been around for many, many years. Buying fittings in Home Depot's "contractor packs" of 25 will be the cheapest, even if you only need 10 or so of a particular configuration. Buying individual fitting pieces is crazy from an economic standpoint.

I have had excellent luck with copper for compressed air to 175 psig. I simply dislike threaded joints in any material. For some reason, I always wind up with at least one leak somewhere that is not easy to correct whenever I do anything with threaded joints. I've never had a leak with a soldered copper joint. Besides, it's faster and easier than threaded pipe.

Don't be hesistant about learning to solder copper joints. Read the handbook how-to section and jump right in. You'll find that your first joints are best done with the fitting pointing upwards such that you are looking down on the joint. If you plan your work well, many of your joints can be done in this configuration. Just don't put the fitting itself directly in a vise that would draw heat away from it and don't apply the flame directly to the solder itself. An air-acetylene torch is best but an inexpensive air-MAPP gas cylinder/torch combo will work. Air-propane can work also but MAPP is hotter and I would choose that as the best alternative to air-acetylene. Oxy-acet or any oxy-fuel is too hot in my opinion for any soft soldering. Silver solder/braze, yes; but not for soft solder.

Rod