desiccant purge

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desiccant purge

Postby painter john » Sun Aug 16, 2009 1:49 pm

Hi all,
Since we dont use desiccants much over here it's hard to get a users idea of them.I was speaking to a guy who deals with air managment in factories etc and he told me that the desiccant drier can be inefficiant due to the air used to regenerate the desiccant.I was wondering what would the rough cfm loss with a small unit like the cam air/devilbiss ones the dad 500 or similar?The guy said they can use up to 15% of air to purge in some cases.He would probably be referring to large factory cases but is it rhe same in them all.
cheers P.J
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DESICCANT - DRY IT - REPLACE IT

Postby Hub » Mon Aug 17, 2009 5:27 am

Hi PJ,
The air management guy is correct, BUT the key word here is REGENERATE - neither of the units you mentioned perform that function.
Each of those units have a sight glass containing litmus paper down stream from the desiccant chamber. Litmus paper changes from blue to pink when the desiccant is spent / saturated. At this point either replace the desiccant or take it out and dry it.
The two most common types of desiccant are;

Activated Alumina - is generally white in color - even when spent

Silica Gel - is blue in color and changes to pink when spent .

An advantage with Silica Gel - when dried it turns back to blue.
Cheers,
"HUB" :)
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Postby painter john » Mon Aug 17, 2009 8:16 pm

As helpful as ever Hub,many thanks.
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NO MORE CAH

Postby Hub » Tue Aug 18, 2009 3:56 am

PJ,
Did you install a system :?:
Cheers,
"HUB" :)
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Postby painter john » Tue Aug 18, 2009 1:04 pm

Hi Hub,no i didnt get anything yet .I've tried snap on ,devilbiss,iwata and sharpe amongst others over here and nobody does these small point of use desiccants.I wanted to find someone over here to make replacement beads easier to source,although i believe they can be dried as you stated.Can the beads in a bag system be oven dried?
I can get a used ref. unit from a local guy who deals/works in factory air management ,not the same guy who told me about the purge so he has no vested interest barr selling me the drier, for about €350.
So i'm not that worried if i cant get a desiccant although the guy with the ref. drier is very very hard to track down to get the thing of him,it could be another month.for air breathing what way around do the filters go with the desiccant ,particulate,coalesing,charcoal,desiccant filters or other way round.
cheers again P.J
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Postby Hub » Tue Aug 18, 2009 1:12 pm

Good Morning PJ,
I have a friend in the UK, I'll ask him to do a little gum shoeing for us and get back to you.
Cheers,
"HUB"
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Postby painter john » Mon Feb 22, 2010 9:18 am

Hi Hub ,I finally got myself a desiccant dryer ,sourced here in Ireland so at least it's quick and easy for me to get service items.
The question I hope you can help me with is do i put the dryer before my 3 stage air breathing unit or after?? if before it do i need another oil seperator before it?
It's not a traditional desiccant dryer as you's would know it but i think it's basically the same,a domnic hunter ATP tool protector.It has white'sh coloured beads in a cartridge that turn pink/red when wet but on the bottom of the unit it states" air discharge may contain carbon monoxide or other contaminates which will cause death or serious injury.Do not breath this air directly or indirectly in a confined space".
if I use my 3 stage air breathing unit can i breath the air or is it a no no.
Cheers P.J
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Postby Andy T » Mon Feb 22, 2010 6:45 pm

Sounds nasty John :shock:

I'd contact the manufacturer directly if I were you just to be sure. That's a pretty stern warning they've given.

Did refrigerated dryers not suit your needs? Fit and forget, with none of the above drawbacks.
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Postby ryanbrown999 » Tue Feb 23, 2010 3:51 am

John, your dessicant will go last always. The only time there is a filter after the dessicant would be another filter to possibly catch dessicant dust. I think they use a coalesing for that.

Another thing is you really don't want to breath the air after it has been through the dessicant. Over in the states most systems will use two airlines. One for spraying and one for breathing. You will want your breathing hose before the dessicant unit.

http://www.autorefinishdevilbiss.com/do ... 9-F%29.pdf

This link shows a manual for a devilbiss unit for breathing air and dessicant.
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Safe Breathing air / clean dry spraying air

Postby Hub » Tue Feb 23, 2010 7:18 am

painter john wrote:Hi Hub ,I finally got myself a desiccant dryer ,sourced here in Ireland so at least it's quick and easy for me to get service items.
The question I hope you can help me with is do i put the dryer before my 3 stage air breathing unit or after?? if before it do i need another oil seperator before it?
It's not a traditional desiccant dryer as you's would know it but i think it's basically the same,a domnic hunter ATP tool protector.It has white'sh coloured beads in a cartridge that turn pink/red when wet but on the bottom of the unit it states" air discharge may contain carbon monoxide or other contaminates which will cause death or serious injury.Do not breath this air directly or indirectly in a confined space".
if I use my 3 stage air breathing unit can i breath the air or is it a no no.
Cheers P.J


Hi PJ,
Heed the warning, your breathing air should come off prior to the desiccant unit. Also prior to the desiccant there should be a water separator and an oil coaleser to protect the desiccant. HOWEVER the desiccant has nothing to do with the carbon monoxide, that comes from the compressor itself. The reason you don't want to breath the air after the desiccant is because, if the desiccant is doing its job the air will have Zero humidity and that would be harmful to your mucous membrane. Check with the manufacture because I don't think you'll need a particulate filter after the desiccant. If the cartridge is solid it will have one built in and if its a bag type, the bag itself acts as a filter and will filter out particulate down to 1 micron.
Cheers,
"HUB" :)
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Postby nzgrip » Tue Feb 23, 2010 7:24 am

You could go to your local Scuba Dive Shop and find out what they use in the filters on their compressor and use that in your filter, no problems breathing that air.
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HUB COMMENT - ON REFRIGERATER DRYERS

Postby Hub » Tue Feb 23, 2010 7:59 am

Andy T wrote:Sounds nasty John :shock:

I'd contact the manufacturer directly if I were you just to be sure. That's a pretty stern warning they've given.

Did refrigerated dryers not suit your needs? Fit and forget, with none of the above drawbacks.


Hello Andy,
If you want ZERO dry air, Refers wont cut it. The very best refer can only lower the dew point to 35 degrees Fahrenheit and most only claim 38 degrees F. and at 50% ambient humidity that would leave about 22 to 28% CAH. Next time you see a fairly fresh paint job that looks starved & has gone flat or pinched and or won't stay rubbed, Don't Blame The Paint or yourself - check the percentage of CAH.
Cheers,
"HUB" :)
Desiccant or Membrane dryers will lower the dew point to negative 40 degrees F.
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HUB COMMENT / QUESTION

Postby Hub » Tue Feb 23, 2010 8:15 am

ryanbrown999 wrote:John, your dessicant will go last always. The only time there is a filter after the dessicant would be another filter to possibly catch dessicant dust. I think they use a coalesing for that.

Another thing is you really don't want to breath the air after it has been through the dessicant. Over in the states most systems will use two airlines. One for spraying and one for breathing. You will want your breathing hose before the dessicant unit.

http://www.autorefinishdevilbiss.com/do ... 9-F%29.pdf

This link shows a manual for a devilbiss unit for breathing air and dessicant.


Hi Ryan,
Do you use one of these DeVilbiss units ? If so which desiccant type does it have in it? Also what brand of fresh air unit do you use.
Cheers,
"HUB" :)
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DV PIPING DIO

Postby Wilson T Hall » Tue Feb 23, 2010 8:58 am

Hey Doc,
Did you look at the DV link :?: what do you think :?:
WTH
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Postby painter john » Tue Feb 23, 2010 9:28 am

Thank for all the help guys,I contacted the domnic hunter helpline and the area rep.
The helpline said not to breath the air as the dryer is only actually a mobile tool protector for air guns etc.
The rep said similar saying that although the air coming through it isnt toxic even with my breathing filters he wouldnt rate it of a good enough quality as the dryer will only take out moisture for an air tool,even though he understands in the real world people breath air through the filters without air dryers he and the service helpline recommend,due to the purge of their proper breather/dryer, a refridgerated dryer for breathing air.
They have the proper desiccant/breathing air setup but it is a purge type which uses 18% air volume and thats the only desiccant breathing dryer they recommend due to beeing able to say 100% for sure the air is clean and dry,but expensive.
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