2G2BT* filter claim

[cobob]

http://www.highlandwoodworking.com/i...OD&ProdID=2180

Can this really be true? 1u filter bag for $30? I was going for the polyester canister but now... maybe not.

[big tim]

$23 and yes that's true. I don't think that's exorbitant.

Tim

[mpauly]

Link takes me to the 14"x24" bag for $24, but they have a 20" bag as well for $29. Note that you'll need two bags (upper and lower) and will still likely have less surface area than a canister. All in all not a bad deal, but I'd still go for a canister for the easy of cleaning/emptying.

Michael

[LCHIEN]

pleated filter canisters still have advantages.

Bags filter characteristics change as the bag builds up a cake. So when you emty it and put it on, it initially passes a lot of air (low restriction) but does not filter well, letting bigger particles thru.
When a filter cakes builds up on it, it gets more restriction but the cake improves the cut point to the 1 micron.
Unfortunately when the lower bag fills up the filter area is reduced and restriction continues to increase.
Don't forget you should have two bags - top and bottom so your price is more like $60.

With a pleated canister on top, the pleats have somewhere like 6-10 times more filter area than two bags for much lower restriction and more CFMs. The "cake" is not the filtering part so performance is more or less uniform from new to used thru its life. The bottom can be a non-porous plastic bag that makes cleaning up so much more clean and easy. Usually the pleated canister filters have a manual beater bar that flips the pleats to release packed in fine dust and help it operate better.

Overall, the canisters have better technical characteristics. Yes, they cost more; you get what you pay for.

[LinuxRandal]

Loring

Since this does have some filtering ability, and a lot of us have/use preseperators (trash can), would this be something one might want on the base (fine bag pleated filter on top), to increase airflow, due to the loss from the can?

[LCHIEN]

Loring

Since this does have some filtering ability, and a lot of us have/use preseperators (trash can), would this be something one might want on the base (fine bag pleated filter on top), to increase airflow, due to the loss from the can?

"this" being fine bag on the bottom? or what?

[LinuxRandal]

"this" being fine bag on the bottom? or what?

Yes, the fine bag on the bottom instead of a plastic bag.

[LCHIEN]

Yes, the fine bag on the bottom instead of a plastic bag.

regarding ulitmate restriction.
so two fine bags would be better than on fine bag, one non-porous plastic bag. lets call that the baseline

2 stock bags is actually worse in restriction they say, this can happen because the fine bags have a larger percent open or aspect ratio.

two fine bags with a pre-sep will always be worse restriction wise than just two bags, you have added restriction wtih the pre-sep. BUT one saving factor is that by catching chips in the presep can then you won't be gradually blocking off the lower bag (should still be catching some fines, tho) and losing that airflow.

Airflow with a pre-sep and two fine bags will always be worse than a canister and worse than a canister with pre-sep. since the canister alone is always better than 2 fine bags which is better than on fine bag.

Restrictions just add on top of one another.

is that an answer?

[LinuxRandal]

Maybe I am reading this wrong, but what I was thinking was this fine bag on the bottom, along with a canister on top.

Thereby adding just a tiny bit of additional breathing room (since using a trashcan separator w/baffle) and limited fines seem to make it to the bag.

Or is it a lack of sleep on my part?

Thanks

[LCHIEN]

oh, I didn't understand.
With the canister having so much more area that the bag, it won't reduce the restriction very much. IN equivalent terms to electronics its like paralleling a large resistor with a small resisitor... the net resistance will be very close to the value of the smaller one.

The air flow resistance will be goverened by the lowest resistance when they are in parallel (since the air can exit either once inside the ring)... e.g. the canister.