Compressed air piping discussion.

[Griffin]

I do this for a living. I deal in compressed air systems that are measured with thousands of horsepower and tens of thousands of cfm. Here's a couple of my guys working on a 12,000 horsepower air compressor:

Now then, a few things about compressed air components.

PVC pipe - No. Synthetic compressor lubricants break down standard pvc glue, causing pvc piping systems to leak at every joint within a couple years, and eventually fall apart. Furthermore, the heat and pressure over time softens the pvc, causing the pipe lengths to sag between hangers.

Black iron - Long the industry standard, advantages are strength and ease of construction. Disadvantages are rust, scale buildup, flow restrictions (pressure loss) due to rough internal surface and susceptibility to scale buildup. Also when scale breaks loose it can clog up and damage downstream components.

Copper - Used frequently, use silver solder to connect joints. Mapp gas is fine with silver solder on pipe diameter up to 1". The only real disadvantage is cost of components and it takes some skill to assemble.

Extruded Aluminum (Transair, Infinity, Airnet, etc...) - Relatively new (20ish years old), very strong, doesn't corrode, easy to assemble due to push-to-connect type connectors. Is very expensive per foot, and the fittings are more expensive than black iron joints, but makes for a durable, easy to install, long lasting system. Requires special tools to install, usually these can be rented from the piping supplier.

Transair video: http://www.youtube.com/watch?v=hFiY9C03XDI

Mechanical water separation systems knock out liquid water, but do nothing to remove vapor and lower the pressure dewpoint of the air. That means that the air is still pretty much saturated at the temperature and pressure your tank is at. When the air expands as it's released to atmosphere, it cools and water vapor will condense out, ruining your paintjob.

Water removal for painting purposes needs to be done with either a refrigerated or desiccant type dryer. Refrigerated dryers are fairly expensive and rarely seen in home shops. The desiccant type can be as simple as an inline filter cartridge with a desiccant canister in it that can be recharged by being heated in an oven several times before replacing. For home shop use, this is usually the best alternative. Search Ebay for something like "Beach polyclear" and you'll find them for a relatively inexpensive price.

Oil carryover from air compressors is a common source for fisheyes in paintjobs. There are commercially available chemicals to mix in the paint to eliminate them, or you can install an inline coalescing filter to do so. The Beach filters also remove oil, but the oil cannot be removed by baking the desiccant element, and continues to build up in the desiccant, shortening the element life. A small coalescing filter from a company like Norgren, Wilkerson, Parker, SMC, etc.. can be found for most small shop applications for under $100.

There are some compressor lubricants that are silicon-based. DO NOT USE THESE IF YOU PLAN ON PAINTING. Silicon and modern automotive paint do not mix. Your paint will be full of fisheyes if contaminated with silicone.

 

[rustybronco]

Did you think I just recommended against PVC for no reason?
Ray.

No I didn't. It's just quite a bit of the time not all the facts are known. Like the article Jim linked, not all pic tubing is the same. Some types are not pressure rated and with the ones that are, we're they used with in its design parameters. It's always nice to know who what when and how.

 

[rustybronco]

Griffin, the particular manufacturer of the coalescing filter I bought States not to use a polycarbonate bowl if your compressor uses synthetic oil. I didn't know that synthetic oil affects the solvent glue used to weld PVC together, but my compressor uses a conventional hydrocracked lubricant so I wasn't too greatly concerned as the unit I bought uses a metal bowl.

I have another question for you but it will have to wait until I can type on something other than this tablet.

 

[Guest]

there is lots of pvc and reinforced pvc air line out there commercially available and safe to use for up to 200 or 300 psi working pressure. ( 12000 hp is over kill for a garage)
there are no real issues if used properly. I have never glued it, there are special fittings, but they are pretty cheap.( compression type. but specific to air line )
like some body mentioned already, pvc or vinyl / plastic air lines are industry standard for air brakes etc on heavy trucks and equipment. a pretty harsh environment compared to a garage.
Plastic lines for air are everywhere, all kinds of pneumatic controls, industrial robots and paint booths.....
flexible so it can be easily "fished" if you'd like an air line to the house, or perhaps put the compressor in the house so it would be nice and quiet in the garage.
works for waterlines as well.
I have yet to see an all plastic air drier, not a desiccant filter, a drier
http://www.eaton.com/Eaton/Products...HoseFittings/IndustrialHose/PCT_261862#tabs-2

 

[rustybronco]

Griffin, although this discussion is about air line piping for the most part, the ultimate goal is the removal of moisture from the compressed air. It's removal will include a d.i.y. inline desiccant system as shown in post #10 of this garage journal thread. http://www.garagejournal.com/forum/showthread.php?t=131919 But as I said before, I'm getting ahead of myself.

It seems so far that PVC isn't the best choice for air distribution piping, and considering it's a poor choice thermally, I'd like your opinion of using copper piping to lower the pressure dew point of the compressors discharged air - trying to condense as much liquid out of the system before being connecting up to the water filter.

Do you think the use of copper piping would go a long way towards reducing the amount of water in the discharged air, or is the copper piping a relatively small factor in the whole process?

 

[Griffin]

there is lots of pvc and reinforced pvc air line out there commercially available and safe to use for up to 200 or 300 psi working pressure. ( 12000 hp is over kill for a garage)
there are no real issues if used properly. I have never glued it, there are special fittings, but they are pretty cheap.( compression type. but specific to air line )
like some body mentioned already, pvc or vinyl / plastic air lines are industry standard for air brakes etc on heavy trucks and equipment. a pretty harsh environment compared to a garage.
Plastic lines for air are everywhere, all kinds of pneumatic controls, industrial robots and paint booths.....

PVC brake lines? Really? I'd like to see a link to that.

PVC stand for Poly Vinyl Chloride. Do not confuse polyurethane tubing with PVC. Do not confuse polyethylene tubing with PVC. Do not confuse nylon with PVC.

flexible so it can be easily "fished" if you'd like an air line to the house, or perhaps put the compressor in the house so it would be nice and quiet in the garage.
works for waterlines as well.

Flexible PVC air line? I'd like to see a link to that as well.

I have yet to see an all plastic air drier

Right here pal..... http://www.beachwestfilters.com/Mer...de=BWF&Product_Code=F-GGC&Category_Code=F-GGC


Not all plastic and synthetic tubings are created equal. Just using any "plastic" for pneumatic systems without understanding the pressure ratings, temperature ratings, and chemical resistance of different polymers is what gets people killed.

 

[Griffin]

Griffin, although this discussion is about air line piping for the most part, the ultimate goal is the removal of moisture from the compressed air. It's removal will include a d.i.y. inline desiccant system as shown in post #10 of this garage journal thread. http://www.garagejournal.com/forum/showthread.php?t=131919 But as I said before, I'm getting ahead of myself.

It seems so far that PVC isn't the best choice for air distribution piping, and considering it's a poor choice thermally, I'd like your opinion of using copper piping to lower the pressure dew point of the compressors discharged air - trying to condense as much liquid out of the system before being connecting up to the water filter.

Do you think the use of copper piping would go a long way towards reducing the amount of water in the discharged air, or is the copper piping a relatively small factor in the whole process?

Copper will act as an aftercooler for your compressor, but it won't lower the dewpoint of the air.

When air is compressed, a tremendous amount of heat is generated (obviously). Everything else in the atmosphere around the compressor intake is also compressed as well as the air (i.e. water vapor, hydrocarbons, fine dust particles that get past the inlet filter, etc...). What comes out of your compressor and goes into the tank is actually a mixture of hot air, water in vapor and liquid forms, hydrocarbons and compressor lubricant in a mist form, and small particulates (generally under 10 microns in size). The air is super saturated with water, and is going to be approximately 160 degrees F coming out of the compressor.

The air/water vapor/liquid water/oil mixture goes into the air receiver, where it expands, cools, and, unless there is a load using air downstream, stays. The tank acts as an aftercooler, cooling the air and condensing more liquid water out of the compressed gas mixture. The liquid water and oil settles in the bottom of the tank. The air is still saturated, but as it cools, there is less vapor per cubic foot of air contained in the air, because cooler air cannot hold as much water vapor as hot air. For every 20 degrees F that air cools, the amount of water it can hold at saturation level is cut in half.

Without either a chemical or refrigerated air dryer, the air is still saturated, and the pressure dewpoint of it will be whatever the air temperature is. Running the air through mechanical cyclone separators will slightly increase the velocity of the air as it moves through the separator, dropping the temperature a few degrees and condensing a little more vapor out, so they only provide at most 2-3 degrees F dewpoint suppression. So if the air in your tank is 80 degrees and 150 psig, you have a pressure dewpoint of 80 degrees. If you start using an air gun which will allow air to flow out of the tank and through the separator, the action through the separator will cool the air down to, say, 77 degrees, and the cyclonic action flings the water to the outer walls of the separation chamber, which allows it to run to the bottom of the chamber and out the drain. You now have a 77 degree dewpoint. If the temperature in your garage is 85 degrees, as the air moves through the air pipe, it will slow down a bit from the separator (larger flow area, like a river widening after a bend and the current slows), and also pick up some heat from the ambient air on the outside of the pipe. The air may warm up to 82 degrees before getting to your airgun. So long as the compressed air temperature remains above 77 degrees, you won't see any liquid water in the air, although it will feel slightly damp if you blow it onto your hand.

The problem is there is still a LOT of water in the air, it's just in a vapor form. That vapor can condense and clog up sandblasting nozzles and it can chemically react with paints and lacquers. The oil vapor in the air can do the same, contaminating any surface it comes in contact with. Body shops spend money for air dryers and multiple step coalescing filters for this reason.

If someone wants to get the same quality results as a professional body shop, they're going to need to invest in the same type of equipment. The homemade desiccant dryer you linked to is fine. It's essentially the same concept as the Beach product I linked to in my previous post.

 

[Crankthat]

May have already been covered in this thread possibly not.

From making snow.
Air and water snow guns.
The friction of constant air running through a pipe or hose will cause heat and that may cause moisture.
When the pressure/air is in constant release the air becomes super cooled by the release.

Try and make your pipe runs as long of sections as needed.
The fewer turns/bends/connectors the better.
The less fittings the better.
Keep everything as smooth inside as possible.
Keep your pipe lines the same diameter going into each other.
Every time you compress or expand the air in your lines you cause more friction therefore more moisture.

This will help your system stay drier.
It also helps to keep your compressor intake off the ground.
A moisture separator is still recommended for many attachments.

Hope this is of help.

 

[Crankthat]

Just read griffins posts.
WOW!

 

[rustybronco]

Griffin, I appreciate your taking the time to respond and your expanded answers. Looks like I will be building a desiccant dryer in the near future.

 

[850 Combat]

My dad used PVC in the early 80s for compressed air distribution in the garage of the house I now rent to my nephew. it hasn't developed leaks in the joints in a 'few years" I have put a coupling in it where there was damage from an impact.Fortunately, the impact was when there wasn't any pressure on the system, or there would have been more than likely a very dangerous explosion where sharp pieces of shattered PVC would have been flying through the air. I'm wondering if PEX would be suitable as a replacement. This compressor is an industrial unit sourced from a multi bay auto repair shop. It is equipped with a large condenser with a cooling fan on it. My dad painted numerous cars and motorcycles with it over the years, including one of my Nortons.

Any thoughts about PEX?

 

[Griffin]

PEX is a polyethylene compound, so is probably fine for compressed air usage. Be sure to check the pressure and temperature ratings for the specific item you're considering though. It needs to be rated for at least 180 degrees F and 200 psig if you're using a two stage, 175 psig compressor.


Back in the early '90s, there was a company that went through the upper Midwest selling compressed-air specific PVC piping systems, with a "lifetime" warranty. It was a quarter the price of black iron, with about 1/10th the labor. Lots of smaller shops (less than 100 horsepower of compressors) and a few larger shops bought the stuff.

Within five years, that company was bankrupt and out of business from warranty claims, but the guys who had worked there personally made a ton of money, so they didn't really care. I replaced miles of that stuff in the late '90s/early '00s with rigid metal pipe of one type or another.

 

[SVSooke]

That desiccant filter looks like the ticket Dale.Might even be able to find a suitable pipe in the "boneyard" at workIf not it shouldn't be that much to buy.

 

[rustybronco]

One section of pipe with two end caps suitably drilled and tapped for the air line connections. A couple of 50 micron screens and a method to support them in the pipe. Desiccant ($16 a quart) and one removable plug in the side of the pipe to check for colour change.

 

[SVSooke]

I was thinking it would be WAY more complicated.

 

[Griffin]

One section of pipe with two end caps suitably drilled and tapped for the air line connections. A couple of 50 micron screens and a method to support them in the pipe. Desiccant ($16 a quart) and one removable plug in the side of the pipe to check for colour change.

I was thinking it would be WAY more complicated.

Bear in mind that you need a coalescing filter upstream of the desiccant to protect it from oil contamination. Desiccant removes water from the air by ADsorption, which means the water molecules adhere to the surface of the desiccant bead. Desiccant ABsorbs oil, and once a desiccant bead is saturated with oil, water will no longer adhere to the surface. Oil saturated desiccant cannot be regenerated by heating it and boiling off the contaminant, so once it's contaminated with oil, it needs to be replaced.

 

[rustybronco]

I knew that oil would contaminate the desiccant. For my intended purpose, limited painting, I had hoped an Exair 9001 filter and a replaceable motor guard inline filter used ahead of the desiccant would go a long way towards increasing it's life. At $16 a quart for the desiccant, it could easily be considered a consumable to be replaced on a semi frequent basis.

But decided it best to get the real thing instead.

Ports are not threaded but I can rectify that.
http://www.ebay.com/itm/Norgren-Oil...ic_Hydraulic_Valves_Parts&hash=item4186236de5

 

[SVSooke]

I have this unit already http://store.norgren.com/us/en/deta...al-drain-general-purpose-filter-w_-metal-bowl ,I hope that it would be good enough to get most of the oil out.With my luck it won't.

 

[Griffin]

I have this unit already http://store.norgren.com/us/en/deta...al-drain-general-purpose-filter-w_-metal-bowl ,I hope that it would be good enough to get most of the oil out.With my luck it won't.

I used to sell Norgren products, it's good quality stuff. But.

The filter you linked to is an F72G. The G stands for general purpose, which means it has a 5 micron particulate element. The element is not rated for oil removal. It will remove some oil, but it is not a specifically designed coalescing filter. The F72C would be a specific coalescing filter. It also is a very fine particulate filter.

So you have a 5 micron filter, you're halfway there. What you need now is a fine particulate/coalescing filter. The coarse particulate is necessary to protect the fine filter, otherwise the coalescing filter element would clog up quickly with particulate. What you want to do now is get hold of a Norgren F72C-2AD-ALO filter, which will get your remaining contaminants down to 0.1 micron particulate and 0.01 ppm oil content.

From the Norgren filter manual:

"Install an F72G filter with a 5 μm filter element upstream of the F72C filter foroptimum coalescing element life."


Typical oil carryover from a reciprocating compressor is 15-20 ppm oil content. That's no good for painting.

 

[rustybronco]

Greg, the 'G' designation at the end of the F72 designates general. If it had ended in a C that means coalescing. Nothing lost as you'll need to use it before the oil coalescing filter.

What do you think of that F72G you have?