Sciencemadness Discussion Board

Compressor dryers?

Quince - 25-10-2006 at 16:12

How do air dryers for air compressors work? Not all the ones I've seen use desiccant materials, so I can't figure out how the others work.

not_important - 25-10-2006 at 22:41

OK, limited knowledge but I'll tell what I know. Just stop the waterboarding, please.

Refrigerated dries work like refrigerators (!) - chill the air so as to condense water in it. May have several sections where one is in 'defrost' mode if the air is being dried to a low dew point. Can be used before or after the compressor.

Membrane driers push the air through porous tubes while venting some of the air to flow around the outside of the tubes and out to the open air. Moisture is ducked through the walls of the tubes and evaporates into the vented air. I believe these have to dump some of the heat of compression so that liquid water forms on the tube walls, where it is wicked on through; evaporation cools the tubes and helps with further condensation.

There's several types that use desiccants and regenerate them on the fly. In one type the hot compressed air is used to heat the saturated desiccant. This can be indirect heating, with a secondary air stream flowing through the desiccant to vent. Alternatively the hot air flows through the used desiccant, then through a heat exchanger that cools the air stream enough for much of the water to drop out. In either case the air then flows through the other, active desiccant bed for final drying.

In another type pressure swing is used. The freshly compressed air flows though active desiccant beds, while used bed have a stream of low (atmospheric) pressure air run through them to remove the absorbed water. Sort of like vacuum drying, except the vacuum is normal pressure, the drying stage is running at 10X or more about that.

12AX7 - 26-10-2006 at 00:18

It doesn't take much as the compression raises the boiling point of water quite a bit, causing it to condense. It also heats up the air, so a condensor needs to remove quite a bit of heat. The water is then drained through a spit valve, so to speak. Dessicants are also used, and regenerated at STP or dehydrated in an oven.

So what's with your sig, mmh?

Tim

Quince - 26-10-2006 at 15:02

Quote:
Originally posted by 12AX7
So what's with your sig, mmh?

Just replying to what you said about me in the microwave drill thread: "IrC, not a bad title suggestion given the nature of our present protagonist."

I figure two eyes for one is a better way to live than an eye for an eye.

[Edited on 26-10-2006 by Quince]

Mr. Wizard - 26-10-2006 at 16:15

Are you asking about the dryers on air conditioner compressors, or about the condensate traps on air compressors?

Quince - 26-10-2006 at 16:16

The latter. Do you have any details on their internal geometry? I'm thinking of DIYing one for my compressor.

[Edited on 27-10-2006 by Quince]

Mr. Wizard - 26-10-2006 at 16:39

The water formed in a compressor is due to the rise in pressure and the subsequent cooling after the air leaves the compressor. The partial pressure of the water is the same as it always is at ambient temperature. This of course leaves the air oversaturated with water and it condenses out along the tanks, pipes, and hoses as it cools. Some of it remains in a fog or mist, as does some of the compressor oil. The condensate traps for tools usually just have a screen or loose filter to facilitate the coalition of the fog into droplets. The ones used on paint sprayer applications may use active chemical or dessicants, because of the higher need for pure air. Don't forget to drain the compressor tank, as that's where the most water collects and the most rusting takes place. I don't have much more than that.:)

Twospoons - 26-10-2006 at 17:49

Why would you DIY one? They are very cheap.
The ones I have are essentially a block of sintered bronze powder, intended to force the fine mist to form large droplets, which then fall to the bottom of the enclosing plastic bowl. A simple plastic shield stops spray getting into the outlet at the top.

Most have a little drain valve at the bottom for emptying. Fancy ones have a float operated valve so draining is automatic.

You can also buy a single unit that has both regulator and mist trap - this being a lot cheaper than buying the two separate items. Have a look at the SMC website for examples.

Quince - 26-10-2006 at 18:04

Shit, doesn't matter now... the bitch I was going to buy the compressor from sold it to someone else cause I was 1 hr late in calling back...

12AX7 - 27-10-2006 at 06:19

Quote:
Originally posted by Quince
Just replying to what you said about me in the microwave drill thread: "IrC, not a bad title suggestion given the nature of our present protagonist."

I figure two eyes for one is a better way to live than an eye for an eye.


Ah, an emotional response to a statement of fact, I'm not suprised with you.

Tim