Spark arrestors

[coldsteelburns]

I was looking around at spark arrestors for dust collectors again today after seeing
another knifemaker using one on his dust collection system. I remember only find one
some yeas ago that was actually small enough for my shop and that attached to 2-4"
ducting, but I also remember not seeing it directly for sale on the site it was shown
on.

After checking out the one I saw this other knifemaker using on his I went to do some
searching on ebay and to see if I could find one of there perhaps, but instead I came
across all the different types of spark arrestors meant for use on engines, many
ofwhich are much cheaper than the ones made specifically for dust collectors. I did some searching to see if anybody has ever used these in their dust collecting system but only
found one person mentioning that they could "probably be used" for this purpose.

So I figured I'd ask to see if anyone here has some insight regarding these and if it
would be possible to use for my dust collection, or would there be any reason it wouldn't work?

The one directly below sold for engines is only $98, as opposed to $370 that the "In-line SparkTrap" goes for, which is specifically advertised for dust collection systems.

Here is a picture of the In-line Spark Trap for comparison:

~Paul
My Youtube Channel
... (It's been a few years since my last upload)

 

[Stacy E. Apelt - Bladesmith]

Those aren't the right thing for our type and amount of sparks. Most folks use a spark and dust/grit trap. The best commercial one for knife use is called a dust deputy. They have a metal model that sells for $199. You attach it to the top of a 5 gallon ( or larger) steel pail. Put about 2" of water in the bottom when in use to trap and kill the sparks.
https://www.oneida-air.com/inventoryD.asp?item_no=AXD001002&CatId={2C6BB449-99F9-4CB9-BC27-CAF1BB570002}

Many folks use the regular dust deputy, which runs $99. It should work unless you do heavy hogging and send showers of really hot sparks.
https://www.oneida-air.com/inventoryD.asp?item_no=AXD000004A&CatId={6EE79B16-EB63-43E7-8F30-1E06240A24A4}
or
https://www.oneida-air.com/inventoryD.asp?item_no=AXD000004A&CatId={6EE79B16-EB63-43E7-8F30-1E06240A24A4}

Of course you can build a basic "spark Bong" from a metal pail/drum and some exhaust pipe for almost nothing. Use the custom search engine in the stickys and search spark bong and spark trap.

 

[coldsteelburns]

Thanks, Stacy.

I was actually planning on using one in addition to the cyclone system I recently bought. Just as an added measure of security before anything enters the dust collector. Any reason you see it not working for that? I guess the question is, would it hinder the performance of a dust collector, or does it have an air flow similar to the ones made/advertised for dust collection systems, such as the In-line Spark Trap I shared above. I honestly know nothing about the inner-workings or physics of these things. Thanks


~Paul
My Youtube Channel
... (It's been a few years since my last upload)

 

[Stacy E. Apelt - Bladesmith]

Then you just need to build is spark bong.

It is a 5 gallon pail with two pipes coming in the lid. One goes down to about 4" above the bottom (the IN pipe). The other goes only about 1" through the lid (the OUT pipe). I would use a 3" pipe for the IN and a 2" pipe for the OUT to the cyclone. You put a baffle down the center of the pail that stops about 4" above the bottom. It is best to have the end of the IN pipe cut at a 45 degree angle and have the open part face the bucket side. Put 2" of water in the pail and put the top on. Connect the short pipe to the cyclone and the long one to the spark funnel under the grinder. All sparks and the heavier dust/grit will drop into the water. The fines will travel up and out the OUT pipe to the cyclone. This setup will clean the air to a very pure state, and the air can be returned to the shop instead of being vented outside. This is a big advantage in the cold states.

It is best to dump the bucket each day.

 

[Mahoney]

It all depends on how much air you are moving and with what. If you have a shop vac, the steel dust deputy works as well as a much more expensive commercial "spark arrestor" and is not nearly as finicky about the duct lengths on the inlet and outlet. There's no need for water in the can, just clean it out frequently, and especially after grinding a flammable metal like aluminium. However, the steel dust deputy has just about doubled in price in the last year or so.

I'm not a fan of the plastic dust deputy, a well-treated $100 piece of plastic should not break in less than a year.

If you are running a dust collection system with a 4" or larger duct, at the proper airspeed for grinding dust (5,000 fpm) the Nordfab in-line spark trap can work well. It needs 10 "duct diameters" length downstream to be sure the sparks are cooled. Based on my testing it is less picky about length on the inlet side, 4 or 5 duct diameters were enough for the 6" diameter units we have on the belt grinders. It's not recommended for use in a vertical leg, because it will trap some dust, but it is also easy to clean out. How much airflow does it take to reach 5,000 fpm in a duct? 450 CFM in a 4" diameter duct, 700 CFM in 5", and 1,000 CFM in 6".

The in-line spark trap does add a bit of resistance to the airflow, I'm pretty sure Nordfab has a chart based on duct size and airflow that will give you the backpressure in inches of H2O.