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Old 08-01-2004, 10:36 AM
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RED caddy RED caddy is offline
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Default franz's air dryer

Hi all, several computer crashes ago, on a long lost bookmark, I saw a plan for a passive air dryer for shop compressors,I can't remember what board it was on, but it was called "franz's fix" I think. can anybody help me find it? thanks very much. RED caddy ( paul)
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Old 08-01-2004, 11:17 AM
Franz Franz is offline
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There was extensive discussion of the water seperator over on the HoFart board, and I think somebody dubbed it the Franzenator or something like that.
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Old 08-01-2004, 02:55 PM
abooker abooker is offline
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Smile Air Dryer

I'm in the process of building an air dryer for my compressor. What I read somewhere was to disconnect the compressor line from the tank, place an automobile evaporator core ( A/C ) on the compressor air line, put one of those glass bowl dryers ( That's suppose to be an air dryer but never works in real life ) on the output of the evaporator core and plumb that to the input of the tank. You also need to put a fan on the evaporator core. This is suppose to cool the hot air from the tank, as it passes through the evaporator core the water condenses and it collects in the glass bowl. I bought a Grand Marquis Town Car Mark VI evaporator core on eBay for 1 penney and with shipping it came to $10.01. When it comes in I'll buy a 110V fan and assemble the whole thing.
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Old 08-01-2004, 03:58 PM
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I think I remember it over at the good ol' days hobart place, but don't recall how long ago.
John
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Old 08-01-2004, 11:54 PM
Franz Franz is offline
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you kids are just bound & determined to make the old guy work, ain't you.

Seperating compressed air from the water it is carrying is simple, in theory. The amount of water the compressed air can hold is primarily determined by the temperature of the air, the hotter the air, the more moisture it can hold.

Since the objective is to reduce the moisture content of the compressed air, cooling the air gets the job done.
The problems begin here.
Compressed air is flowing from the compressor to the tank rapidly, so you don't have a lot of time to chill it. A second problem occurrs because the air also is carrying sufficient oil from the compressor to emulsify (mayonaze) the water.
By chilling the airstream, between compressor & tank, you acheive an airstream that is carrying droplets of slop, rather than essentially steam. The water and air are still NOT seperate, and the slop wants to adhere to the inside surface of the chiller. These problems can be overcome, IF the tubes of the chiller are sufficiently sized to the airstream, and drainage is employed when the compressor shuts down. if the chiller is not drained, the slop will reduce the effectiveness of the chiller.

Now, about the idea of using an air conditioner coil,
will it chill the air stream, yes
can the chilling be enhanced using a fan, yes
HOWEVER, the fan must be installed to SUCK air thru the coil, and an inlet baffel MUST be installed between the fan and the coil, or you will have a cold spot in front of the fan, and monimal cooling.

So, now we have a stream of slop containing droplet compressed air, headed for the tank. The next goal is to seperate the slop from the compressed air. This is where the fun part comes into play. Lets look at the fruitjar. As we all know, they look pretty, cost money, and you've seen them in use everyplace, cause some engineer designed the air system, and he believed the damn catalog that said those fruitjars seperate water from compressed air. The thing we know is that no fruitjar ever seperated a drop of water from ai airstream. Even guys who paint cars in the back yard and stick the metal fruitjars in buckets of ice water don't manage to seperate water from the air stream, cause the damn fruitjars don't work.

Even though the microdroplets of slop are heavier than the air, they ain't going to fall out of an airstream that is moving faster than Moma's Buick ever did. Objects in motion tend to stay in motion!
So, how the hell do we get the slop out of the compressed air?
The easiest way is to give the slop a cold surface to hang onto. The tank on the compressor is a cold surface, so some of the slop will adhere to the inside of the tank. Of course, you really don't want it in there, and unless you have a sufficiently large tank, that allows for compressor downtime, the slop really isn't going to get a chance to hang onto the inside of the tank.
The second problem with using the tank as a slop collector is the distance between the incoming compressed air/slop and the nearest available cold spot on the tank for the slop to cling to. If you're getting the idea this isn't a good way to go, you're on the right track.

The verticle column water seperator made from 2" pipe works because it does several things at the same time.
First, it cools the air sufficiently to allow the air stream to give up the water content.
Secondly, it provides a cold surface for the slop to cling to, and requires the air stream to follow the cold path on it's way to the tank.
Third, it provides a slopwell at the bottom to collect the slop.
How efficiently the colum works is primarily determined by how much humidity is in the air being compressed, and how cold you can keep the colum.

You can also employ a secondary colum seperator downline, between the tank and air tool, and get more water out of the air. Lindsey has been doing it with sandblasters for 50 years, and it works. Lindsey's units don't work as well as they could though, cause the damn bean counters at lindsey only allow a foot of pipe where 3 feet are needed.

You can make these colums as simple or as fancy as you want to, air or water cooled, and nothing I've found in 30 years of screwing around with this idea takes more water out of compressed air.
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Old 08-02-2004, 09:24 AM
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franz' drier:
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Old 08-02-2004, 09:27 AM
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franz technical drawing made with Aaroncad 1.0 (the non-color version)
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Old 08-02-2004, 11:24 AM
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I have been putting together this unit for my shop. Now it uses all 1/2 inch pipe. My fittings are currently 1/4 so I simply removed the Tee and installed a reducer to make the connection to the 1/4 inch line from the compressor. Not the best I know but it is what I have at the moment. The restriction acts like a expansion valve, since it is in fact what it is. You are forcing compressed air though the 1/4 inch line into 1/2 and as it expands into that volume it cools. Drops a lot of moisture there too.
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Old 08-02-2004, 11:47 AM
Franz Franz is offline
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Hobweld, you're dead on on the refridgeration by expansion being a major contributor to the efficiency of this design.
If you look at the hi tech drawing of the units I make, the air from the compressor is turned 90° and forced along a longer travel path along the cold wall of the pipe. Turning the air definitely increases the efficiency of the unit. Having built quite a few of these units, I can assure you that pipe size is very important to the amount of water removed, and 2" pipe works best.
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Old 08-02-2004, 07:17 PM
stovepoker stovepoker is offline
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I dunno, that contraption looks an awful lot like the one my Uncle
uses to separate the low ends from his corn squeezin's. Are you sure you boys don't have it hooked up backwards?
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