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inexpensive filter/dryer

18K views 41 replies 11 participants last post by  001mustang 
#1 ·
I had started an air line thread and it got down to discussing what sort desiccant dryer/filter I could use on a budget, it was suggested to start a new thread specifically on that- can't disagree.

The Devilbiss QC3 was suggested, and found it around $150 online. Are there other suggestions that might be a bit cheaper/better or is that sort of the one for light painting use.
 
#3 ·
This is about as cheap as you can get.
I have an extra tank, the same size as the tank on my 3 HP compressor, 20 gallon.
I run a hose from the regulated out on the compressor, to a water trap/ filter mounted on the second tank. The air inlet on the second tank is on the top, pointing down, in the center. The air out to the paint gun is on one end of the second tank. I have a pressure gauge on the gun, that has a built in restrictor.

I use a $79.00 HVLP gun, from Home Depot.

This is how I set it up for painting. Regulate the air out of the compressor down to about 40 PSI, and put the second tank close to what I am painting. Adjust the pressure at the gun down to what I want, with the trigger pulled.

This setup allows me to paint more or less continuously, with a HVLP gun, and an old 3 hp Craftsman compressor. The compressor cycles on and off when I am painting, and spends more time off, rather than on.

This is my theory on why it works. We all know the air inside the compressor tank is hot, and has (non condensed) water vapor in it. When the hot air goes through the regulator, the pressure is reduced, and if you paid attention in high school chemistry, you know that allows the volume to increase, and the temperature to drop. The drop in pressure, and temperature causes the water vapor to condense in the air hose going to the second tank. The air also continues to cool a little more in that hose. The water trap can then catch the condensed water, and hold it. Any water that gets past the water trap, simply falls into the bottom of the second 20 gallon. Because the volume inside the second tank so large, compared to the air hose, there is no way any water in the second tank could be blown up to the outlet of that tank. The water just stays in the second tank.

It has been suggested that I move the regulator to after the second tank, because I would have more high pressure compressed air. Although that is true, the air in the second tank would be hotter, and still be holding on to the water vapor. The air has to cool for the water vapor to condense, and be trapped. The air expansion at the compressor mounted regulator cools the air, and a lot of the water vapor then condenses out before it gets to the filter/ water trap, and into the second tank.
 
#5 ·
That system with the second tank is what we used to call a "Thump tank" and it does indeed work quite well. Another common setup I have seen uses a large pipe set vertically or, as was often done, a large drive shaft was used. This does work quite well and does for the reasons described just keep the "Thump tank" on regulated pressure.


BTW shouldn't be Physics class?
 
#6 ·
Gas laws = chemistry, or maybe physics, I do not know. I remember in the chemistry class I took in my first term of community college, on one page of the textbook, there was a diagram of the pressures inside the cylinder, of an engine, during the four stroke cycle.
By the way, knowing Algebra comes in real handy when you are figuring out the compression ratios of an engine.
 
#8 ·
oldred said:
That system with the second tank is what we used to call a "Thump tank" and it does indeed work quite well. Another common setup I have seen uses a large pipe set vertically or, as was often done, a large drive shaft was used. This does work quite well and does for the reasons described just keep the "Thump tank" on regulated pressure.
Interesting. That drive shaft or large pipe "Thump tank" would be easy to wall mount and get out of the way.
 
#15 ·
i dont do a ton of painting, but i do some and have never had a problem.

all i have is a water separator at the compressor with over sized pipe on both sides of it, so the air slows down as it goes through it.

then in to 1/2 pipe that goes into a tee (with a drain in the bottom) up and across the top of the garage and back down to drain/outlets.

from there it goes up to another water separator/filter and reel.

again, i have never had a problem, but i am going to get some disposable dryer/filters for use at the gun for cheap insurance :thumbup:
 

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#16 ·
I've played with a few combination, built a few different setups and finally have a simple, cheap setup that works.

One, nothing is going to work well at the compressor, the air temp is just too high there. You need to get at least 20-30' of line between it and the drier assembly.

Do a web search for a "franzinator," it's a separator similar to what was already described here as made out of a driveshaft... After making a few I will say that the HF separator basically does the same thing and by the time you build your own, kill all the leaks... you'll be better off spending the money at HF:
http://www.harborfreight.com/desiccant-air-dryer-97686.html


my setup ended up with about 30' of 1/2" from the compressor to my filter/separator assembly. That is connected to a standard inline air filter (one of the deals with the clear bowl on the bottom, mine is actually the big Kobalt one), connected into the HF drier, and then that is connected to an motorguard M60, the outlet of that assembly is split into 2, one going straight to the basement hose reel, the other to the garage.

This setup works great for painting, running a plasma cutter, blasting cabinet...
 
#17 ·
My Sharpe dessicant dryer has an inspection window so you can tell when dessicant is spent. Pretty easy to replace spent dessicant in Sharpe. My Sharpe seals well. Sharpe is aluminum.

Does HF model have a dessicant inspection window?
Easy to replace media in HF?
HF seal ok?
Does HF rust inside?
 
#18 ·
heh, he said cheap... your sharp probably cost me more than my whole setup incluing all the fittings to get it to connect together, assorted valves so I can turn off any part, quick connects...

that said:
- no inspection window
- the only hard part about swapping desiccant is the way I mounted it (literally, untread cap and dump it out, in theory with it mounted to the wall you can unthread the bottom cap, dump it, unthread top cap to refill, no disconnecting air lines or anything)
- No leaks- that was the big hassle with home built, I spent a lot of time chasing leaks with my older setups
- No rust that I've seen, though I don't see why it couldn't. that is the reason that I have the motorguard after it, nothing steel comes in contact with the air on the other side of the motorguard.
 
#19 · (Edited)
The pressure drop thing is a great idea!

This is what I did ... an idea spawned from a post by another member here on HR.com.
It seems to work very well. Very little condensate even makes it as far as the filter.


What you can't see in this pic are 4 ball valves and a small "manifold" to collect and drain any water that gets trapped in any of the legs of the cooling tower.

It's all plumbed using 1/2"copper water line, and uses truck air-brake hoses to isolate the vibration from the compressor.
 
#21 ·
001mustang said:
I suppose you could drop even more condensate if regulator positioned upstream cooling tower.

BTW, I like 66 GMC 305E V6.
Really?
I had always thought that cooling / conditioning the air was the first step, and that regulating the pressure was the last step in the delivery process.

Yep, that 305E was sure a reliable and torquey mill.
Didn't see a lot of them up here, though.
Most Canadian model 910's were equipped with 250 or 292 inline 6's and a 3-on-the-tree. I've seen a few 283 4 spd, and a couple with Powerglides, but zero TH350 until the 67-72 showed up.
 
#23 ·
I run my regulator as close to the hoses that I'm using as possible, more pressure in the lines means more delivery. Even then usually I keep it set at 90psi, and most things that need less also need a fairly high volume, like a spray gun or blast cabinet, so I put a regulator right at the inlet to whatever it is...
 
#24 ·
The biggest reason why I use the regulator upstream, at the compressor is that is where it is on the compressor. Ideally, I would use some metal pipe to cool the air down, as close to the compressor as is possible, because the hotter the air is, the more heat it will transfer into the pipe. For me to use a down a down stream regulator, I would have to go and buy one. I gpt lucky. The second tank was just given to me.

Remember the title of this thread had the word "inexpensive" in it.

I like the idea of the wall mounted manifold to cool the air.
 
#25 ·
True enough ... this setup turned out to be not all that "inexpensive".Probably well over a $100 when the dust settled.

The 1/2" x 8' copper tubes were about $20 each, plus all of those elbows, and of course the ball valves and air brake hoses. Not to mention a little material being scrapped along the way.

As with most of these inventions, the budget seems to multiply exponentially! LOL
 
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