Recharging my air scrubber

[Randy Digby]

I changed the method of retaining the charcoal to the use of cheesecloth back in March and felt it was time to do a full recharge. I have changed the pre-filter three times since then. I also needed to clean the dryer duct hose that runs form the laser to the scrubber as it tends to collect dust in the spiral grooves. I thought I would take a few pics as I put it all back together so you can see my cut on a scrubber. I know there are several designs in use and as long as they work - then good for us.

I pull a vacuum thru my scrubber back to the laser to solve any foul air smells from air leaks, so the air from the laser enters the unit from the top thru the dryer hose and PVC pipe fitting you see on the left of the first pic. You can also see the 1/4" screen wire gride that supports the charcoal charge. The grid is supported by a piece of closet shelving material - the kind with the heavy wire runners about every inch or so.

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Cheesecloth is cut and placed on the grid. The extra serves several purposes. It seals the prefilter around the edges and it lets you remove the charcoal charge by lifting the cheesecloth out. This was my first time removing the charcoal and it worked great.

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Charcoal charge is added.

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Pre-filter (12" x 24" x 1") is installed with cheesecloth pushed in to seal area between filter and box sides.

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The top is replaced. Since I pull a vacuum, simple toggle clamps and weather seal works fine.

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And then to utilize the space, I have a material rack I place on top of the scrubber to keep our most used sheets at hand.

http://farm5.static.flickr.com/4127/4956661443_525491f092_z.jpg

Back in business. Have a good holiday weekend everyone.

[Tom Bull]

Looks excellent. With winter coming I am thinking about all the hot air I will be blowing out of the house. Where do you get the charcoal?

[Randy Digby]

The activated charcoal comes from General Carbon in Patterson, NJ. If you are going to vent inside, you need to consider a HEPA filter also. I vent outside and use the scrubber to kill the odors so the neighbors don't get restless.

[Frank Defert]

Hi Randy,

Good post with great pictures! I do have a couple or three questions.

I noticed the size of your scrubber 12 X 24 and the inlet is off to one side, any reason for this ? How thick is your carbon bed? How much air flow is lost through the scrubber and the bends in the hosing?

I am going to install the hepa filter option and try to reuse the air instead of exhausting it outside. I live extremely close to my neighbours and am worried about the exhausting air sound. Any ideas on how to quieten this down?

Thanks .... Frank

[Randy Digby]

I noticed the size of your scrubber 12 X 24 and the inlet is off to one side, any reason for this ?

Space restrictions led me to put the inlet on the back corner. The crud buildup on the pre-filter is fairly even leading me to consider it is a non-issue.

How thick is your carbon bed?

About 2-1/2". I started at 1-1/2" and would set the laser up doing a large raster job on plastic and then go outside and siff the exhaust. At about 2" the smell went away. The laser is in an upstairs laundry room that we dot'r use (for laundry) so I vent out of the dryer vent.

How much air flow is lost through the scrubber and the bends in the hosing?

Hard to tell...some, of course. I don't use a large blower, mainly for noise. The blower is under the laser and pulls out of the bottom of the scrubber through a 6" hose. My nose tells me when it's time to change the pre-filter as well as a test I developed. I hold a sheet of paper near the vent grid adjacent to the laser bed and have learned to tell what condition the pre-filter/scrubber is in by how fast the paper is sucked up against the grid. Not very scientific, but it works for me every time.

I am going to install the hepa filter option and try to reuse the air instead of exhausting it outside. I live extremely close to my neighbours and am worried about the exhausting air sound. Any ideas on how to quieten this down?

My exhaust noise standing outside under the vent is no louder than our clothes dryer vent. Again, my blower does not sound like a fighter after-burner, nor does it move air like one. It does evacuate the laser bed very well to the point that I seldom have to clean the optics (my indicator).

A word about noise reduction: Back in another life - about 30 years ago - I was tasked to carry out a noise reduction project in a very large plastics plant with lots of high frequency noise blowers and pneumatic material delivery lines. If my memory serves me, high frequency noise is best dampened with thin, dense material. We purchase a heavy rubber type product (may have been inpregnated with lead or some other dense material) that was about 1/8" thick and glued, taped, wrapped, stapled it to pipes and wooden sound enclosures built to surround the blowers. One of the things easily missed when doing noise abatement is heat dissipation. We toasted a few blowers before ther time until we learned to provide ventilation to the enclosures.

Hope this helps.

[Frank Defert]

Randy,

Thanks for the oustanding response! Detailed answers to every question. I am now ready to build my scrubber.

Thanks .... Frank

[Bill Cunningham]

I noticed that you are using a plastic/metalized dryer hose/pipe on your box. If you are drawing air through that, watch that stuff closely, or replace it with a flex metal one. They are not built to withstand a vacuum at all, and the inner liner will delaminate and collapse, blocking all airflow. What helps with the delamination, are the oils, and other crude going out the pipe.. A good layer of crud, could also cause it to catch fire if a spark goes in. I've never had a fire, but one I was using certainly did collapse. Switched to a flex metal right after that!

[Randy Digby]

Good thought Bill. That is one thing about my set-up that bugs me. The discharge pipe on the laser is some metric number smaller than 4" (I know, my machine specs should have it, plus I can measure it) and when I did a quick measurement early on, I couldn't find a hose the correct diameter. The correct fix is to have a sheet metal shop make up and adapter and then replace the hose as you suggest. "Good" hose will not collapse enough and still get a good seal, at least not as good as the aluminum foil dryer hose. Every time I change the pre-filter, I remove the hose, carry it outside and clean it out with compressed air. You are correct, it does build up a considerable amount of crud. I don't do wood or cut acrylic becase of the spark/fire hazard. The only spark I've ever seen when cutting laminate is from yellow over black - go figure. Not only am I concerned about dust build-up in the hose, but also the dust layer that builds up on top of the pre-filter.

Thanks for proding me. Time to slide the laser out, measure the opening and sketch up a transition piece.

[Bill Cunningham]

Well like the old saying says.. If at first it does not fit, wrap it up with tape and...Stuff...:D