"Continuous bleed" on desiccant air dryer?

[myredracer]

Just finished all the piping and filtration for my home shop. Bought a nice 2 quart Wilkerson #X25-04-000 desiccant air dryer (used on ebay for good price). Very substantial piece...

It has a moisture indicator on top that has litmus paper in it that changes color if it detects moisture. There is a sticker on it that says "continuous bleed". The manufacturers website doesn't say how this works. I filled the compressor to 125 psi yesterday evening and when I checked it this morning there is no air in the tank. Bummer. I refuse to believe I created a leaking joint somewhere so am guessing that it is due to this bleed feature.

Does continuous bleed mean that there is a constant bleed of a small amount of air to the atmosphere? I would assume if that's the case, the amount of air being released is insignificant in normal daily use. The indicator sits on top of the dryer and I'm wondering if there is any good reason to remove it and seal it with a gasket? Or just forget about it? I'll have to get some gas leak detector and check the indicator and joints just for piece of mind. I saw a photo of one of these air dryers somewhere that the owner had added a sight glass moisture indicator on the side of it (won't bleed air). It's pretty easy to remove the bowl occasionally to see if the silicone beads have changed color.

 

[engineer2]

Here is a link to how they work.
http://www.airbestpractices.com/sys...atmentn2/desiccant-dryers-ten-lessons-learned
They continuously bleed saturated air through the tower that is being regenerated. Timers typically switch between the two towers. They consume a lot of air and are generally best when your compressor needs to operate 24/7. Their advantage is they can achieve really low dew points.

 

[myredracer]

This is the Wilkerson unit I have. It's about 5" wide x 21" tall. It's just a canister with beads in it. The 2nd photo is the indicator on top. I don't see an orifice anywhere that would bleed the air. The continuous bleed is just to make the indicator work.

 

[OCD]

Just finished all the piping and filtration for my home shop.

Pics?

 

[Fixnair]

It appears to be a dual tower regenerative dryer. And yes there is a constant purge through the tower not drying the air. What they do is take a portion of the air that has been dried, from the tower that's on line, and purge that air through the tower that's off line to dry the desiccant. It is expensive to operate but very efficient at drying the air. Your purge rate could be 15% of the rated capacity of the dryer.

 

[myredracer]

Pics?

For sure, once the bugs are all worked out and I've cleaned the mess up...

 

[myredracer]

It appears to be a dual tower regenerative dryer. And yes there is a constant purge through the tower not drying the air. What they do is take a portion of the air that has been dried, from the tower that's on line, and purge that air through the tower that's off line to dry the desiccant. It is expensive to operate but very efficient at drying the air. Your purge rate could be 15% of the rated capacity of the dryer.

This unit is a single cylinder can. It has a 3/8" or so tube to the bottom in the center and air is simply blown into the bottom and exits out the top (or vice versa). I wiped some leak detector all over the top and there is no air escaping. Maybe it bleeds internally and a small amount of air bypasses the air going through the beads? Devilbiss has an air dryer with the identical moisture indicator on top. I'll see if they have any info. on it.

The dryer is rated 25 cfm and 15% of that would be a lot.

 

[engineer2]

It's a single stage dryer. Does it look like this except maybe longer?

X-Series manual desiccant dryers offer the most cost effective method to remove moisture form very low flow compressed air systems or those which are only used infrequently. Atmospheric dew points as low as -100°F are obtainable with units available for flows up to 25 SCFM. These dryers are an excellent choice for point-of-use applications such as paint spraying, laboratory instruments and small control air systems.

Color change of indicating silica gel or moisture indicator provide an instant status of the dryer. Color-change silica gel can be regenerated for reuse.

You change the beads after every 11,000 SCF of air or when the indicator says to. You heat the saturated beads for your next use.
The driers usually ship new with an extra jug of beads.