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View Full Version : Air assist filtering of oil and water for co-axial air assist



john banks
03-26-2012, 8:26 AM
Using a twin piston (oiled) belt drive 3HP compressor, what sort of filtering would you use for co-axial air assist to protect the lens? Planning to run 30 PSI approx as this in earlier testing gave superb results on wood cutting with minimal clean up or masking required, preventing charring of very fine cutout work.

Supplied with the compressor is a green floor standing cylinder which is full of a fibrous material which has some rust stains and leaks a bit. The cylinder is quite rusty from just using once or twice, so we weren't going to bother.

Next is a blue possibly alloy (rust free inside) "compressed air fine filter" which has an approx 10" long cylindrical filter. Planning to use this.

Finally a regulator with water trap and mesh filter, then into the machine where I've installed a solenoid whose control is working well.

Awaiting a few bits of pipe to hook it all up, but wondering if water and oil from the compressor will clog the "fine" filter and whether some sort of coarse filter should be used too?

Eric Ucci
03-26-2012, 11:11 AM
John,
Have you made any mods to your machine/nozzle/air assist to get good results at 30 psi cutting wood. I plan on cutting wood as thick as possible, so I'm considering some alterations to the air assist. Are the hoses supplied with the machine capable of 30 psi?. I bought this compressor:

http://www.tcpglobal.com/airbrushdepot/tc60.html

It goes to 57 psi but is low volume. Do you think this will deliver the volume you need for wood cutting?

Thanks
Eric

Shenhui 1490 150w reci

Joe Hillmann
03-26-2012, 12:14 PM
I have never found a commercial made water traps do there job very well. They do fill up with water which means they are taking some out of the compressed air but a lot (I would say 90%) of the water is missed by them. I plan to build something like this http://www.ihcubcadet.com/forum/messages/22745/226882.jpg this summer to condense the water out. And if that isn't enough I will submerge it in a bucket of cold water to allow it to condense out even more water. From what I have read to get enough surface area for this type to work you need it about 3 feet long. Although this will work for water I don't think it will help with oil.


If you do a search for Franzinator you can find out how to build one. Supposedly it is best to mount it between the compressor and the tank.

Eric Ucci
03-26-2012, 2:21 PM
I found this filter here by Devilbiss with a desiccant filter cartridge.
http://www.amazon.com/QC3-3-Stage-Filter-Dryer-Unit/dp/B002PR8ZXK/ref=sr_1_15?ie=UTF8&qid=1332785698&sr=8-15
It looks like it would do the trick

Gary Hair
03-26-2012, 3:03 PM
You could always try a Franzinator - seriously, google it

ray hampton
03-26-2012, 3:42 PM
Supposedly it is best to mount it between the compressor and the tank.[/QUOTE]
the air do not contains water when it come out of the compressor but it do contains steam, placing a section of air hose into a bucket of cold water will condense the steam

Gary Hair
03-26-2012, 4:17 PM
placing a section of air hose into a bucket of cold water will condense the steam

Not really, in order to condense the water out of the air you need heat transfer, air hose is a poor heat conductor. If you want it to work efficiently you really need to use copper - just like a moonshine still, there is a reason they used copper.

ray hampton
03-26-2012, 4:25 PM
Not really, in order to condense the water out of the air you need heat transfer, air hose is a poor heat conductor. If you want it to work efficiently you really need to use copper - just like a moonshine still, there is a reason they used copper.

this is true but that is not why they use copper tubing, white lighting taste better when copper are used and copper last longer

john banks
03-26-2012, 4:26 PM
Thanks, bit beyond my skills to build Franzinator.Eric, the air hose in the machine looks like typical air line that is rated much higher.I tried narrowing the nozzle and that worked great with short focal length, but we want to use longer lens and have lots of airflow and pressure at the work.

Edit, maybe I will build something to cool the air, I like the sound of an oil cooler which will get airflow from the belt drive.

Bill Cunningham
03-26-2012, 7:35 PM
If you build a two tube unit, fill the first one with marbles, feed it from the bottom through a tee, with a drain valve on the bottom port. (marbles provide a huge amount of surface area for moisture and oil to condense on) From that you go through a tube of activated alumina, with about 1 inch of ordinary felt at both ends at full operating pressure (100-120 psig). This will filter, and drop the moisture in the air to 'breathable' levels. The regulator to drop to 30psig should be the last thing in the chain. Alumina is cheap, and can be back flushed with warm air to re-activate, or simply replaced once a month. I have used this basic filter system on a much larger automatic back flushing unit to provide surface supplied breathing air to divers for 30 years. I'm pretty sure it will clean and dry the air for any low pressure need.

Rich Harman
03-26-2012, 8:04 PM
the air do not contains water when it come out of the compressor but it do contains steam

The air does contain water, but it is not steam. Steam is a gas in it's own right. To turn water into steam it must be at or above the boiling point. The boiling point rises as pressure rises. At 100 psi it would need to be at something like 350 degrees in order to turn to steam.

ray hampton
03-26-2012, 8:57 PM
Rich, are you sure that you need heat to turn water into steam ? a compressor will heat air quite high, when your compressor reach 120 psi, what is the air temperature ? how many gallons of air will it take to fill a 30 gallon tank to 120 psi ? if the intake air is at 70 degrees F what will the temperature rise be at 120 psi ? 2x120 psi

Gary Hair
03-27-2012, 2:20 AM
Rich, are you sure that you need heat to turn water into steam ? a compressor will heat air quite high, when your compressor reach 120 psi, what is the air temperature ? how many gallons of air will it take to fill a 30 gallon tank to 120 psi ? if the intake air is at 70 degrees F what will the temperature rise be at 120 psi ? 2x120 psi

This is all about the physical properties of water and air and the temperature/dew point spread. With any given the amount of moisture in the air, there is a temperature that the moisture condenses, that is the dew point. The higher the air is above the dew point the more moisture it can hold, that is described as humidity and is measured as a percentage. It's not steam, it's evaporated water. In order to "remove" the moisture from the air you must cool it, that's what the coil does in a still, and what a water trap does for a compressor. I don't know what the temperature of air is when it is compressed, but I do know it is warmer than the surrounding air so it holds more moisture. When it cools in the tank some of the water condenses out, just like a cold glass of beer does, especially in the humid Southern states.

If you want to get all of the moisture out of the air then I think you need some pretty low temperatures, but the main goal is to reduce the temperature of the air below the temp of the surrounding air so that it won't condense any moisture on your equipment.

There are only so many ways to do this and they all revolve around cooling the air and giving the moisture a place to collect so that it doesn't make it into whatever equipment you have attached to it - paint gun, laser, sandblaster, etc.

All of this is some pretty basic stuff I learned in private pilot ground school. I can also spew info on adiabatic lapse rates, the Bernoulli effect and sublimation - but they aren't anywhere near as interesting as moisture in the air...

Gary

john banks
03-27-2012, 5:54 AM
I want low enough water content so I don't fog up the lens with mist, or deposit oil on it, but also enjoy the benefits far more airflow and pressure appears to bring to laser cutting wood.

It is interesting to hear how long dessicant lasts before it needs a regeneration, which will surely depend on the type of dessicant, mass of it, how much water it is removing etc. Offsetting this against the setup hassle of a more complex installation.

Does anyone here use just a small water trap with a big compressor and do they get issues with fogging up lenses?

Joe Hillmann
03-27-2012, 9:54 AM
I want low enough water content so I don't fog up the lens with mist, or deposit oil on it, but also enjoy the benefits far more airflow and pressure appears to bring to laser cutting wood.

It is interesting to hear how long dessicant lasts before it needs a regeneration, which will surely depend on the type of dessicant, mass of it, how much water it is removing etc. Offsetting this against the setup hassle of a more complex installation.

Does anyone here use just a small water trap with a big compressor and do they get issues with fogging up lenses?

In my home shop I think I have a 30 gallon tank with a little store bought water trap. In the summer when I am running it the trap fills about 1/4 full within a couple minutes and then water starts spraying out of what ever tool I have connected to the hose.

The trap is after the tank, if it matters.

I also think that the plumbing after the compressor is usually totally ignored it is even hard to find information online about how to hook up an air compressor to get dry air even though wet air can cause early failure in air tools and complete failure of some work processes. Usually when someone buys a compressor they put it in the corner, plug it in and hook a air hose to it and away they go.

ray hampton
03-27-2012, 1:18 PM
This is all about the physical properties of water and air and the temperature/dew point spread. With any given the amount of moisture in the air, there is a temperature that the moisture condenses, that is the dew point. The higher the air is above the dew point the more moisture it can hold, that is described as humidity and is measured as a percentage. It's not steam, it's evaporated water. In order to "remove" the moisture from the air you must cool it, that's what the coil does in a still, and what a water trap does for a compressor. I don't know what the temperature of air is when it is compressed, but I do know it is warmer than the surrounding air so it holds more moisture. When it cools in the tank some of the water condenses out, just like a cold glass of beer does, especially in the humid Southern states.

If you want to get all of the moisture out of the air then I think you need some pretty low temperatures, but the main goal is to reduce the temperature of the air below the temp of the surrounding air so that it won't condense any moisture on your equipment.

There are only so many ways to do this and they all revolve around cooling the air and giving the moisture a place to collect so that it doesn't make it into whatever equipment you have attached to it - paint gun, laser, sandblaster, etc.

All of this is some pretty basic stuff I learned in private pilot ground school. I can also spew info on adiabatic lapse rates, the Bernoulli effect and sublimation - but they aren't anywhere near as interesting as moisture in the air...

Gary

steam is evaporate water but not all evaporate water is steam, the clouds is one, fog is two, I am not the one that coined the word "steam " for the compressor fog problem, do we need to rewrite the whole internet