Drying air for spray gun

OK I’m probably going to get some stick here about you get what you pay for but I’ll go ahead anyway.

I was in the market for a small compressor for general work around the house/workshop and the local hardware store had a GMC going out for about $140. It came with a spray gun. I can hear the moans - compressor and gun for $140 – you can guess the quality of the gun! However, the compressor will keep up with the gun at the 60psi recommended and for painting the weatherboards on the workshop and house it seems to be OK.

My question is, what sort of filter/dryer is required? The local supplier wanted to sell me a Norgren F70 filter ($45) but I don’t think that will stop the water. Although water is not a problem with water based paints, I would like to use it to apply finishes in the workshop. What sort of drying system is required? How much should I pay.

I have a regulator with a filter the filter is little more than a glass bowl it works OK. Can't remember what it cost.

You need a water trap, one of the inline ones are all you will need, they are not very expensive.

Here is a link to an inline trap, I have one just like it, got it from Bunnings or some such place, can't remember now.

Water Trap

Being commercial I ran all my air through a rather large Stork Air Dryer/Filter. It was 80% desicant. Then through an oil filter to remove any traces of oil (and there was always some whenever it was drained). Then through 4 seperate water trap regulators. Over kill? Nup definitly not for the quality of finish I had to achieve.

Hi Shane
The oil filters, are they just off the shelf stuff or did you make it yourself?
Cheers, Allan

Just off the shelf. it looks similar to a water trap regulator but bigger and cast not plastic so ya can't see if there is anything in it until you release the drain valve at the bottom.

And I thought that all I needed to spray the paint on was a compressor and spraygun. To get what you blokes are talking about I'll need to renovate my bathroom (sorry! paint shop) but I need something to improve the finish as I'mm sick of marks on the finished product. One problem is that what I paint are usually childrens toys and I seem to waste more paint than I use just stirring the paint and washing the brushes and I can't get spray cans in the colours I want. Any suggestions?:confused:

Spraying you'll probably find you'll waste just as much if not more by the time you clean the gun and the overspray issue.

How about an airbrush if the parts are small - less to clean = less waste.

Also if you get good with an airbrush, you can also do some real fancy work with different colours - make the kids scream for more :)

The way I understand the water traps is they are nothing more than an expansion chamber with a bowl to trap any condensed moisture passing through with the air flow - bit like a cyclone preseparator where the pressure drop lets things fall out of suspension.

I've watched my air seperator, its like you say, the air pressure drops in the bowl and the water condensates onto the bowl.
A bit like the low air pressure on a plane wing when you see the cloud of vapour. No not a woodwork plane, before you can say it. :) :D
Cheers, Allan

here's a simple solution that works for me.

I took the main regulator off the compressor & relocated it (more
later)

I obtained a second reciever (tank) from a local tool shop I added a few fittings & adaptors.

the air runs out of the compressor at the presure set by the presure cut out ( about 110psi)

a 5 metre length of hose goes to the second tank.

the main filter regulator is connected after the second tank.
the main reg runs at about 90psi

the air is then fed into the gal piping system.

for spraying I use a second (small) filter regulator fitted with a guage the reads 60psi full scale.

since putting this system in place I no longer get water in my piping or in my filters for that matter.

the keys for moisture removal in cooling & slowing the air flow.

no filter regulator will remove vapour(gasious form), the water (or oil) must be in droplet for the trap to work.

I used to get a lot of water geting past my filter reg & being a real pain.
This solution is cheap & it works.
I have never seen any trace of moisture in my secong filter or in my finish.
I use some high demand tools for long periods & still have dry air.

Can't recomend this enough.
:D

Quote:

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no filter regulator will remove vapour(gasious form), the water (or oil) must be in droplet for the trap to work.

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Mine does....

That I would like to see.

A unit that seperates one gass from another?

I suspect it must precipitate the liquid somehow.

Tell?

Air entering the compressor is subjected to an adiabatic process, increasing the temperature as a result of change in volume or pressure without the addition of heat energy. Subsequent cooling of the air without varying pressure will result in the release of moisture droplets when the air becomes saturated.

If your airline was long enough (50 – 100 feet say) cooling could take place and the moisture released by cooling subsequently trapped. If the pressure is decreased (at the nozzle of the spray gun) cooling will also occur and any water not removed will also be released (condensation). Condensation is the change of state of water from gaseous form to liquid form.

A simple water separator would be a centrifuge that would swirl the air prior to delivery, flinging water droplets out of the stream for collection in a bowl. Such a device could remove drops as small as five or ten microns. Adding a coalescer to the line would remove even smaller particles (0.01 microns) thereby eliminating moisture problems at the nozzle.

Some airlines I have seen have a gradual slope back towards the compressor to assist with water control. When the line drops back to floor level a drain point is incorporated so that the lines can be drained at both the compressor end and the outlet end on a regular basis.

Soundman I guess Shane is saying that his unit filters out water particles so small that the airstream at the gun is dry for all intents and purposes.

my asertion remains.

all water trap devices I have seen rely on getting to contaminant into liquid form small in size but still liquid.

this includes the big desicators.



the only way I could imagine to truly extract gas form contaminents would be chemical, ie passing the air thru some form of desicating crystals that then have to be rejuvinated or replaced.

Soundman

I wasn’t necessarily suggesting that your scientific assertions were incorrect. I was however suggesting that the microscopic size of water particles extracted by a coalescer were extremely minute. To give some indication of the size of 0.01 micron consider that 1 micron = 0.000001 metres (m) or 1 x (10 to the power of -6) metres.

I am not up on the theory of a coalescer but I imagine it works on the principle of coalescence. That is the collision of two or more water droplets that subsequently combine and form a larger droplet. If water vapour (water in a gaseous form) could be induced to form microscopic droplets that subsequently coalesce, the resulting larger droplet may then be captured by a minute filtration system and removed from the air. This would in fact remover water from the air by mechanical means rather than chemical means.

My theory, an expert in coalescer design may argue otherwise!

Any takers?

Thanks for the advice folks.

Hee hee!! All I wanted was to stop the moisture spoiling the finish. :p

By the way, talking of finishes. I've just been reading a book called "Understanding Wood Finishing - How to select and Apply the Right Finish." (American Woodworker/Readers Digest)

In my humble opinion a book on a par with the Neil's polisher's handbook. Not so much detail on how to do it but loads of background info on why do certain things and chose certain finishes. Debunks quite a few myths too

Its important to grasp where my asertions are comming from.
& the point is
extracting contaminants form cool air is vastly easier because they form droplets far more redily.

moisture traps work much better on cool air.


hope this helps someone.

It was a major revilation to me.

cheers

Soundman,

Correct. The air reaches its ‘dew point’ or the temperature to which moist air must be cooled at constant pressure, to become saturated.

That was my thoughts on the coalescer. If the air in the line is cooled, condensation can be induced and the resulting water droplets filtered out. Coalescence enables the drops to be increased in size so that they may be captured and removed from the air stream. A type of mechanical filtration system to remove water droplets.

Quote:

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Originally posted by soundman
the only way I could imagine to truly extract gas form contaminents would be chemical, ie passing the air thru some form of desicating crystals that then have to be rejuvinated or replaced.

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Bing Bing Bing we have a winner....! :D

Interesting discussion going on here guys, keep it up, I'm learning lots.
My system (about $400 worth) gets used mainly for blowing dust etc, I have noticed the little transparent chamber never seems to have anything in it but occasionally vapour is visible when I squirt my blower. (perhaps I should see my doctor?)
I drain the tanks about ten times less frequently than the instructions recommend (about the same as my car) and get a cupful of rusty water.
I have been wondering whether all this stuff about draining etc really mattered or whether I had an el cheapo filter that didn't work.
The small amount of spraying oil based poly varnish I do has not revealed any moisture problems.
Or is this whole subject a question of what the local climate is like.

Ray