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DC - why mount cartridge filter to bag ring?

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Forum topic by jamsomito posted 03-29-2018 03:16 PM 1369 views 0 times favorited 9 replies Add to Favorites Watch
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jamsomito

432 posts in 845 days


03-29-2018 03:16 PM

I’ve seen lots of installs where the cartridge filter is just strapped to the top of the existing single-stage bag ring and the bag is kept on the bottom. Even lots of installs like this where a pre-separator is involved. It would seem to me that the ring creates another big performance loss as it’s basically another cyclone attached to the system, no? If you have a pre-separator before the blower, wouldn’t it make more sense to ditch the big ring, duct with a 90 fitting directly to the filter and have some sort of clean-out on the bottom? Is it just not enough loss to worry about, or is it an ease of mounting thing? Just trying to figure out the best way to set up my system, within reason.

Background: I just ordered a Wynn filter for my HF 2HP DC. For ages the 35A was the way to go because it fit in the bag ring easily, but recently it seems the recommendation has shifted to the 35F, which is much smaller in diameter. The reason being the F model has a beefier cage on the outside so you can agitate (i.e. beat on it) the dust inside giving better intermittent cleanings between tear-down complete cleanings, and it has a bigger flange that makes it easier to attach in various situations. I was going to buy the 9L which is the one used by ClearVue cyclones and has more surface area – eventually I’m going to keep modding my system piece by piece until it becomes essentially a CV1800 – but when I talked to Dick Wynn, he said these filters have some sort of cage on the inside that he was worried with sub-optimal separation beforehand (like you’d get from a Thien baffle instead of a precise cyclone), it would plug up more quickly from a modded HF setup. So the 35F it was. I got the one open on both ends so I could make my own bulkhead / bucket clean-out and remove it later to stack more than one when I get the cyclone / bigger blower built. For now, I need the system to run as efficiently as possible given the relatively low power of the HF system, which got me thinking about how to attach this filter to the HF and the losses associated with each method. I also don’t want to have to clean out the filter every week either…


9 replies so far

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Rayne

1209 posts in 1958 days


#1 posted 03-29-2018 07:18 PM

This is actually what my next MOD will be for my existing DC MOD. That ring is taking up more space than necessary so I plan on doing exactly as you say, use a long 90 elbow from the DC to the filter directly. Mine is more of a space concern than performance. I just have to find an efficient method to hold the filter up in my constrained corner of my garage.

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jamsomito

432 posts in 845 days


#2 posted 03-29-2018 07:39 PM

Yeah, good point about space savings too. I was either going to mount directly to the wall with some 2×4 framing, or just extend the mount to the floor so it’s not vibrating my home walls.

I don’t see any reason not to direct-duct the filter other than maybe ease of cleanings/attaching. Seems like it would save a fair bit of pressure loss from the bag ring too.

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OSU55

2357 posts in 2408 days


#3 posted 03-29-2018 09:25 PM

IMO direct ducting to the filter will result in more difficult and more frequent filter cleanings. I have the HF dc with the 35A filter, with a Thien baffle. I do get fines passing the Thien (as expected). A few minutes tapping the filter and blowing air back through is all the cleaning needed. I havent removed the filter in a couple of years.

I used to have an issue with the fines just getting picked up again, until I installed an upside down wok in the center of the bag ring which interrupts the cyclonic uplift in the lower bag and prevents the fines from re-entering the filter. Air flow measured the same before and after the wok was installed.

With a real cyclonic separator the direct filter flow may work fine, but not with a Thien style. That will result in the filter having to be removed and cleaned, and nowhere for all those fines that shake loose during removal to go but into the duct below, which then fill up the shop vac when cleaned out. If you must direct mount the filter, direct flow down into the filter vs up, and hopefully you are very diligent in not allowing the separator can to overfill and fill the filter with chips from carryover. For me the couple of sq ft required for the bag ring is much preferred vs the downsides with other options.

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jamsomito

432 posts in 845 days


#4 posted 03-29-2018 09:46 PM

For me, footprint isn’t really an issue, though my shop is only about 100sf so I’m sure I could cram something else in the 2sf it clears up, haha.

OSU55, how much fines do you get in the bag and how frequently do you empty it? It just seems to me that the inch or two (or more? No idea really) of precious static loss is a high price to pay in overall airflow for a couple less filter cleanings per year (could be way more than that for all I know too).

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bbasiaga

1243 posts in 2414 days


#5 posted 03-29-2018 11:27 PM

I guess if you have a clear bag or can on your preseperator and can be 100% sure you aren’t full, then the bag on the back end doesn’t matter.

But planing or joining fills up the 31gal can I have on my preseperator fast. And I look over and can see chips entering the bag and stop. If that isn’t there, you pack your fan and filter full if you are not careful.

Brian

-- Part of engineering is to know when to put your calculator down and pick up your tools.

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jamsomito

432 posts in 845 days


#6 posted 03-29-2018 11:50 PM

Ok so it’s more of a security thing. I can get that. But wouldn’t a big cyclone system have the same issue? Why don’t they use them in those systems?

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bbasiaga

1243 posts in 2414 days


#7 posted 03-30-2018 01:29 AM

They may have high level warning lights or auto cutoffs on larger or industrial systems. Or even a clear cyclone. Could also alarm the differential pressure on the cyclone to know if the bottom has plugged. All of this is stuff you can do at home too, if you have the know how and money. Or you can just take the risk and try and manage by checking the drum level a lot.

Brian

-- Part of engineering is to know when to put your calculator down and pick up your tools.

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OSU55

2357 posts in 2408 days


#8 posted 03-30-2018 01:19 PM

I dont get a lot of fines, but I dont have a drum sander or something else that generates them. I use a shop vac with a ros. My main generator of fines is the TS.

The pressure drop is easy enough to measure. Diy manometer is easy to make with clear tubing and a yardstick. Just measure at the same place before and after bag ring removal. Keep everything else the including filter condition the same – my guess is it is minimal, but testing provides the answer. Flow difference for A 1” wc difference at the suction point can be calculated.

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jamsomito

432 posts in 845 days


#9 posted 03-30-2018 01:30 PM

OK, well thanks for the thoughts everyone. My filter is on it’s way. Once it’s here I’ll take a few weeks to get around to reconfiguring everything. I already have some plastic tubing I can use for a manometer so if I do some tests with/without bag ring I’ll be sure to post it here.

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