water extraction from compressed air

Hey guys,

Sorry if this post is in the wrong section - it's the closest section I could find :)

I want to paint some motorcycle fairings. I've got an air compressor, and understand that i'll need to remove moisture from the air.
I'm planning on buying a 3m coil of copper tube from bunnings ($15) and putting it inside a spare fridge/freezer so that it's nice and cold, then running the air to it directly from the compressor, and a moisture trap at the end before going into the sprayer.

Does this sound like the way to go? I've got no idea about spray painting with compressed air, so forgive me if this is a dumb question :)

Cheers,
Michael

G'day Michael,

That idea has been done plenty of times and works well. You've got it right.

I just run the air line into two long lengths of steel water pipe (vertical to shed roof) with a trap at the bottom of each. Air goes in first one which has a spiral steel baffle in it, crosses to the other pipe at the top, comes down to outlet above second water trap and out.

After that the airline goes into a Schrader water trap and then the regulator.

I never have to drain the Schrader - all the moisture comes out in the two pipes (first one mainly).

Not rocket science but works extremely well at spraying shed temperatures.

Yes, I've sprayed a few mc petrol tanks and guards etc :)

Cheers

Rob

Rob, thanks for telling us your method but I'm a bit unclear as to where the water traps are placed. Could you post a few pictures of your set up for me.


Peter.

Hi Peter,

Here's some photos of my setup. It's just made up from some spare water pipe and fittings I had laying about.

The air from the tank goes into the pipe on the right. The air to the regulator exits from the pipe on the left.

Both vertical pipes have a section below the air connectors to hold moisture run off and a tap to drain it off.

Moisture condenses out best as you go from a high pressure area to low pressure area - so it's best to make the pipes larger as you move the air through the system to get maximum differential in volume. The current setup should be feeding in on the left, but I did it this way as the right hand pipe has a larger water trap/collector and I don't empty it very often.

Smaller to larger would be a bit better, but won't make a lot of difference - it works extremely well even with both pipes the same diameter.

The more metal mass in the pipes the better.

In the middle photo you can see the rusty mark on the floor where I've drained off the condensed water.

Cheers

Rob

The coiled pipe in the fridge will work providing you can drain the coils. A better idea would be to buy one of those portable air tanks and fit it in the fridge. The theory is that the air will spend more time in the tank than in the coils so will drop more water out. In the coils the air will not stop flowing whereas in the tank it won't stop but it will slow down radically.

Thanks alot for the replies guys, looks like I'm on the right track. Thats a nice setup you have there Rob.
I'll get started in a couple of weeks installing a coiled pipe into the freezer. I'll post up some pics of my setup when done :)

Cheers,
Michael

There are a couple of issues here.

firstly annealed copper tube that comes in coils is not fit for carrying compressed air.

If you have a length of copper tube rupture at 120psi and let go the whole reciever of air the distruction can be massive.....it just flaps arround like a razor sharp flail........Havn't seen it myself, but a mate used to install compressed air systems for a living and he assures me this sort of failure is simply horifying.

If you are ever going to use copper for compressed air it must be pipe and fittings specificaly rated for the pressure and purpose.

NOW...to a real solution I know works because I use it every day.

So you have an ordinary compressor of any kind.....the air that comes out of the pump is pretty danm hot.....check the pipe that leads from the pump to the tank...carefull don't burn yourself.

The air in the tank and the tank its self that the pump is mounted on will be pretty warm too......you can check that for yourself.

Ya standard filter reg will only extract water in droplet form....if the water or oil or whatever other crap is in vapor form it will go straight thru almost any water trap........so we need to cool the air.

The easiest, most effective way I have found is to fit a second reciever ( tank) to your system.
This tank can be a purpose baught tank rated for the pressure or the tank from a dead compressor. Size is not important but arround the same or similar capacity as the tank on the machine works best all round.

Important is that the tank has an inlet and a seperate outlet preferably at oposite ends of the tank or seperated by as much distance as possible.

take you main filter reg off your compressor and come out of the compressor mounted tank at full pressure, using at least 1 meter of hose..2 or 3 meters is better.....go into one end of the tank and out the other and into your filter reg.

Before Ininstalled this system I used to get water pissing out of my airtools and filling my airlines when using high demand tools like drills.....my water trap simply could not cope.

Now if find most of the water condenses in the second tank, because it is cooler and the air strean slows significantly there. I get very little water in my filter reg and none in my air lines.
I also run a smaller filter reg for spraying that has a finer filter in it......I have never seen any water in the bowl of this filter reg.

The only time I have seen any moisture in my air, was when I had an extended session sand blasting the interiour of my boat and I had not drained the tank or the main filter reg.

There are all sorts of complicated things including refrigerated driers you can use, make or buy, but the second reciever will give you the best result for the minimum fiddle.

I have several mates who have done exactly the same on different sized systems, none of us would go back to a system that does not run a second reciever.

cheers

Most home air systems use hose/hard lines that are way to small. The bigger the line the slower the air moves and the slower the air moves the more time there is to extract the water. Soundman has just repeated what I said earlier, use a second tank and putting it in a fridge won't hurt at all. Up to one inch of annealed copper pipe has a burst pressure of 200 psi at 100 deg F http://www.google.com/url?sa=t&rct=j...7JAtOSHV7UdKMQ

That does not take into account it being subject being damaged. I myself use 3/4 inch pipe, anything under is a waste of time.

I say again DO NOT...DO NOT used annealed copper pipe for air lines.....on the surface it may seem to be capable of doing the job, but it is not.

Because of the way that it is made and handled, annelaed copper pipe is prone to work hardening and splitting.

Lots of people seem to be prepared to take their chances in ignorance with annealed copper pipe. My friend Barry will not, particularly after going back to a job he quoted and lost. The owner of the workshop reconed he had done the reasearch and had installed non suitable copper pipe......it later failed, fortunately causing nothing but tempoary hearing damage and brown trousers to workers, but the dammage where the fractured pipe had flailed arround and taken big chunks out of timber rafters and roofing sheets was enough to convince all concerned that if copper is used it must be the right stuff and installed by someone who realy knows what they are doing with compressed air.
Needless to say Barry got the job of reinstalling, using the propper materials.

There is huge amounts of poterntial energy stored in compressed air......it deserves more respect than some people give it.

As for refrigeration......unless you are doing high volume spraying, completly un necessary, all you need to do is get the air temperature down to where the vapor will condense into droplets and give it an oportunity to fall out of the air stream.
A second reciever will do that very well for most of us.

If we extract the moisture from the air, before it gets into the lines, we do not have any need to worry about moisture in our air lines or the speed of air flow in our air lines.

Most small workshops run on 1/2 inch ( 12mm) hose and fittings which is perfectly adequate for spraying, nailers and small power tools.
I regularly run lengths of hose in excess of 30 meters, many building sites run lengths of 1/2 inch hose over 50 meters with no apparant loss in performance.

Spray guns that most hobbists and light trade would encounter are pretty low demand items. If anybody spraying is at all fussy they will be running on gun regulators or dedicated regulators close to the spraygun.

Nailing guns and riveters are very low average demand items, and will run very happily on quite long hoses.....in fact for these a length of 1/2 inch hose will act as incresed stored air capacity.

The only time a hobbyist or small trade user will run into high air demand items is, the power tools and the limitation will be the compressor's ability to keep up and not the air lines ability to flow air.

Unless you are running more than a 20CFM compressor or more than 50 mteres you probably, don't need to worry about ya 1/2 inch hoses being too small.

cheers