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Making a Desiccant Air Dryer with Silica Gel

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awemawson:
Having got my CNC Plasma Table up and running I've been giving a lot of consideration to the humidity of the air that I supply to it. Moisture in the air badly affects cut quality and the life of the consumables. I do have a refrigeration style air dryer, and I did resurrect it for the Plasma Table. but to be any use it needs to be switched on for long periods of time, and it draws quite a bit of electricity

(Thread here for the rebuild http://madmodder.net/index.php/topic,11815.0.html )

Now there are all sorts of ways of drying air mainly concerning condensing the moisture and draining it away, but there is another method using Silica Gel that has the useful quality that it will absorb large quantities of moisture, and better still it is re-recyclable by the simple expedient of roasting it in the domestic oven  :ddb:

So my plan was to remove as much moisture as possible with a conventional air / water separator then pass the pre-dried air though a column of Silica Gel.

Ideally the column containing the Silica Gel should be transparent, as it is available in a 'self indicating' state whereby it changes colour as water is absorbed - very handy  :thumbup:

I hit on the idea of using a standard 10" water filter container and modifying it for use as a desiccator. These thing are modestly priced, are transparent (or at least mine is), and are designed to take mains water pressure safely.

awemawson:
Now the input and output of this housing are 3/4" BSP female brass inserts, so connections there are no problem at all. The air needs to pass through the bulk of the Silica Gel, then up a tube leading to the output port. The tube somehow needs to have a filter or gauze on it to stop the desiccant blowing straight through to the output. I hit on the idea of using a sintered plastic compressed air exhaust silencer. They are available in all sorts of sizes, and I chose one with a 1/2" BSP male thread.

Then it was a case of making up an adaptor for the filter lid to take the 15mm copper pipe, and joining on the silencer using a standard compression 'tap connector' - it all went rather well and turned out fine.

Initially I was stumped for a bit of brass stock to make the adaptor from, as I didn't want to turn down the only rather large brass bar that I had in stock - then my eyes fell on a 1" BSP to hose barb fitting, just crying out to be modified  :clap:

I designed the adaptor as a push fit into the bore in the lid of the filter, with an 'O' ring as a retainer / air seal. In the event it turned out that the hole in the plastic lid had just the right taper for it to lock solidly - in fact so solidly I had a bit of a struggle to get it out again  :bang:

The adaptor is soldered onto the 15mm copper pipe.

awemawson:
Now the inlet port is just a vaguely rectangular opening at the top of the filter. To prevent Silica Gel leaking back into the inlet under negative pressure situations (when turning off) I incorporated a fine brass gauze in the opening, bonding it in with high viscosity super glue

awemawson:
Next to add the pre and post filters. The pre filter is a conventional water separator used for it's intended purpose, whereas the post filter, although again a conventional water separator, I'm using it as it has a 5 micron sieve to sweep up any fine Silica Gel dust that might 'get away'

awemawson:
So no more ado - do a leak test. Well first a safety pressure test with it covered in a towel - shame if the poly carbonate filter housing were to explode. :bugeye:

All's well - no violent explosions so then the leak test. I keep a horticultural hand spray on the shelf full of soapy water, and it's amazingly good at finding even the smallest escape of compressed air - but this was sound (I use Loctite 542 thread sealant on this size plumbing and swear by it)

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