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Custom built air dryer for compressed air

rons

Diamond
Joined
Mar 5, 2009
Location
California, USA
I saw a video today about a man who built a dryer out of a 4 inch square box iron 3 feet long.
Standing the box piece on end a 1 inch pipe ran down the middle with a opening at the bottom.
Stainless steel wool was loosely packed inside then the ends were welded. A fitting on the top
of the square box is the input for hot air. The air travels down the box through the steel wool
and then up through the center tube and out the fitting on the top of the box.The bottom of the
square tube was drilled and tapped for a manual drain. He made two of these and connected them
in series.

I don't care for the iron idea due to rust and scale so it made me think about doing something
similiar using 3 or 4 incn copper pipe. When I went to the industrial supply store a 20 footer
of 3 inch copper costs $407. Wow. When I look at some of the crazy pipe arrangements that people
do I decided to look into a design like this.

Why I think this is a good idea is that the larger diameter pipe will slow down the air velocity
and allow better condensation on the stainless steel wool. Any opinions.
 
They're ripping you - even McMaster, which is darn high for materials has 3" x 10ft type M for "only" $180:

5175K142 $180.08 Copper Tubing for Drinking Water, Low Pressure Type M, 3" Tube Size, 3-1/8" OD

You should be able to find it for under $200 for 20ft, or just get a shorter length from McM. BTW, I made my own air dryer from copper tubing similar to what you described, and it works very well. In combination with a coil of copper tubing in a small fridge, I get very acceptable dry air even in the most humid months.
 
I saw a video today about a man who built a dryer out of a 4 inch square box iron 3 feet long.
Standing the box piece on end a 1 inch pipe ran down the middle with a opening at the bottom.
Stainless steel wool was loosely packed inside then the ends were welded. A fitting on the top
of the square box is the input for hot air. The air travels down the box through the steel wool
and then up through the center tube and out the fitting on the top of the box.The bottom of the
square tube was drilled and tapped for a manual drain. He made two of these and connected them
in series.

I don't care for the iron idea due to rust and scale so it made me think about doing something
similiar using 3 or 4 incn copper pipe. When I went to the industrial supply store a 20 footer
of 3 inch copper costs $407. Wow. When I look at some of the crazy pipe arrangements that people
do I decided to look into a design like this.

Why I think this is a good idea is that the larger diameter pipe will slow down the air velocity
and allow better condensation on the stainless steel wool. Any opinions.

I'm wondering what the function of stainless wool is. Lots of surface area? So what? all that surface just holds precipitate so it takes longer to get to a drain.
You wrote "4 inch square box iron", not sure what you mean. If cast "iron", lots of thermal mass there. If square steel tube, also not a good thermal conductor. Either way, not good radiators.

The point is, reducing the temperature of the air is the most efficient way to reduce the moisture content. I guess an iron (or steel) box full of stainless wool could help as long as it is cooler than the input air. For a low volume user it might help somewhat (probably not better than having a secondary receiver [tank]). As air usage increases, the device will just get warmer (less effective at precipitating moisture).

Using a copper container gets you a better thermal conductor, for sure, but not a very efficient radiator. Twenty 1/4" ID tubes flow more CFM than a 1" ID tube and have almost 7 times the exterior (3/8" OD vs 1 1/8" OD) surface area (= radiator). Better to build an array of small copper tubes than an iron (or copper) box.
 
Why not use an air con condenser or similar with a fan or mount it in the beer fridge. Out of the way of course :cheers:

I tried that, with a few car a/c condensers, and they were very difficult to solder on to. The theory was good but in practice the diameter was small and it just didn't work.

In the end I got a length of copper tube from the scrappy and ran it between the compressor (where the air is hot and moist) to the receiver. The air cools in the tube and I have a drain at the bottom. It extracts most of the moisture in the air, and I've never felt a need for any further drying. As mentioned, the trick is to handle the water extraction while the air is hot.
 
Go on craigslist.
Find a junk window air conditioner for free.
Use the condenser and/or evaporator. There is a built in electric fan that can also be used.
 
You don't want a car ac, there small flow high cooling, you want a intercooler you just gotta find one that can hack the pressure!!!!!
 
A snapshot of the video:

vlcsnap-2015-10-13-07h20m43s455.jpg

I would design it so that the it could be disassembled.

I would like to do something like this. I know I could run a long tube at a decline angle with a drain at the opposite end
to cool the air. I want something a little more sophisticated.
 
I'm wondering what the function of stainless wool is. Lots of surface area? So what? all that surface just holds precipitate so it takes longer to get to a drain.
You wrote "4 inch square box iron", not sure what you mean. If cast "iron", lots of thermal mass there. If square steel tube, also not a good thermal conductor. Either way, not good radiators.

The point is, reducing the temperature of the air is the most efficient way to reduce the moisture content. I guess an iron (or steel) box full of stainless wool could help as long as it is cooler than the input air. For a low volume user it might help somewhat (probably not better than having a secondary receiver [tank]). As air usage increases, the device will just get warmer (less effective at precipitating moisture).

Using a copper container gets you a better thermal conductor, for sure, but not a very efficient radiator. Twenty 1/4" ID tubes flow more CFM than a 1" ID tube and have almost 7 times the exterior (3/8" OD vs 1 1/8" OD) surface area (= radiator). Better to build an array of small copper tubes than an iron (or copper) box.

Lots of surface area yes. A larger diameter pipe to slow down the air velocity. Longer contact time for cooling.
 
Here is a photo of mine, minus the fan I mount in front of it blowing on the compressor. This works fine when it is below 70 degrees out. I have since added 60' of 1/2" id copper tube coiled in a tub of water, $80 with shipping. When it is 110 outside the water is below 80 at the end of the day. Water cooling is way more effective than air. Compressor runs at a 65% duty cycle on one mill and I don't have any water in the air. Yeah it's hokey but it works, it's cheap, and it's low maintenance. One other thing, the birds and hornets love the constant source of water in the summer.


Compressor.jpg
 
All of the water traps in my shop are always bone dry. It does help a lot if you catch the water before it reaches your receiver tank, which I now do.
 
There is no way to drain residual moisture. This leads to mold. I looked into using a coil but in the vertical configuration.

View attachment 151580

That could well be a cut and paste of what I have (albeit a somewhat neater coil). I have the hot air at the top and coils angled such that the water flows with the air. There is a trap at the bottom that auto-drains when the pressure is released at the end of each cycle when the pump unloads. Under the trap outlet I have an ice-cream container to capture the oil and water ejected. The system looks bodgy, but is very effective and I've never seen any water past the receiver. If super dry air was required it would be a good basis to remove the bulk of the water before subsequent processing.
 
They're ripping you - even McMaster, which is darn high for materials has 3" x 10ft type M for "only" $180:

5175K142 $180.08 Copper Tubing for Drinking Water, Low Pressure Type M, 3" Tube Size, 3-1/8" OD

You should be able to find it for under $200 for 20ft, or just get a shorter length from McM. BTW, I made my own air dryer from copper tubing similar to what you described, and it works very well. In combination with a coil of copper tubing in a small fridge, I get very acceptable dry air even in the most humid months.

Copper tubing is cheaper than copper pipe. I think the quote I got was for type K. Type M is tubing.
 
Copper tubing is cheaper than copper pipe. I think the quote I got was for type K. Type M is tubing.

I went with M as it still has plenty of pressure capacity (~430psi), my outlet pressure is 95psi, didn't see a need to go with K. It's been years and the system still works very well. It is ugly though, hence my reluctance to post pics...
 
I have been down the long copper pipe road and gave up and spent a little on a harbor freight cooler ,,, it ran me like $300 with free shipping and it works GREAT.
1/2" NPT in and out and just plug it into a 110V outlet and be done .... Normally I`m the first one to say harbor freight sells only junk but they screwed up and built a good air dryer for once.
 
rons, if I have mold in my tubing what must my receiver tank look like? It's been 2 winters without mishap. I don't think there is enough residual moisture to worry about.
 
rons, if I have mold in my tubing what must my receiver tank look like? It's been 2 winters without mishap. I don't think there is enough residual moisture to worry about.

Your receiver tank is probably still in some stage of rust. You should have seen the 120 gallon tank I cleaned up.
Those port plugs are pretty hard to unscrew. If the construction stage is to screw them tight and then weld the flanges
on the tank might explain that. Anyway there was more than a inch of crude. So I took action on my restoration.

Cleaned out the tank of all rust and dried it out. Poured in a couple of quarts of DuPont industrial primer and
rolled the tank in all orientations to coat the tank. At the last stage I tilted the tank so that a ramp was formed
from the leftover paint. Now any water flows down the ramp to the drain port. I have looked in the tank a few times
since the painting ten years ago and there is no rust. Just a white/gray finish. I also unscrewed the drain port pipe
and ran my finger on the inside. No rust, not even on the threads.
 








 
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