Modification of Two-Bag Extractor

[SLM]

Good morning,

As I re-establish my workshop, I’m rationalising my dust extraction, including finally upgrading from a bag to a cartridge filter. My principal extractor in a two-bag unit, similar to the one pictured. I will only have one machine attached at a time, through the 125mm inlet.

Would there be any issue with removing on bag? I can remove the Y-shaped duct, and bolt the motor/fan unit directly to the collector. The benefits would be a smaller footprint and only having to buy one cartridge filter, not two.

Is there a flaw to the plan??

Cheers

 

[Yojevol]

Good morning,

As I re-establish my workshop, I’m rationalising my dust extraction, including finally upgrading from a bag to a cartridge filter. My principal extractor in a two-bag unit, similar to the one pictured. I will only have one machine attached at a time, through the 125mm inlet.

Would there be any issue with removing on bag? I can remove the Y-shaped duct, and bolt the motor/fan unit directly to the collector. The benefits would be a smaller footprint and only having to buy one cartridge filter, not two.

Is there a flaw to the plan??

Cheers

Only a couple of things I can think of:-
1. The CofG will be raised and you'll need a new structure to support the fan.
2. You'll be halving the airflow so the pipework will need to be reduced from 125mm to 100mm to keep the air speed up, but I expect you've already considered that.
Brian

 

[SLM]

Only a couple of things I can think of:-
1. The CofG will be raised and you'll need a new structure to support the fan.
2. You'll be halving the airflow so the pipework will need to be reduced from 125mm to 100mm to keep the air speed up, but I expect you've already considered that.
Brian

Thanks Brian,

Yes, I’d already thought through the ramifications of the required support, so it’s just the airflow considerations that I’m interested in.

Please excuse my ignorance on the subject; though I’ve a rudimentary understanding of this stuff, I’m sure you and others here have a more in-depth knowledge and understanding!

When you say the air flow is reduced, do you mean by the removal of the Y-shaped duct, or by the reduction in surface area of the final filter?

Thanks for you input.

 

[SLM]

Oh, it might be worth mentioning that I’m toying with the idea of adding a cyclone or battle.

 

[Doug B]

I went down a similar route last year, like yourself I wanted one 125mm flexible outlet that I could move to each machine as I used it, this is what I came up with

This was only a single bag unit with an adapter on the impeller housing from 6” to two 4” ports, I ran 6” ducting from the impeller housing to the cyclone & then a 125mm flexible hose from the cyclone which attaches to the machines.
I had to alter the pipework from the impeller outlet of the filter but this wasn’t difficult.
As I’d expected there is a drop in suction from adding the cyclone but it still clears the the machines of shavings, emptying the drum is far easier than faffing about with bags which never sealed adequately but the biggest bonus for me is fine dust in particular from the lathe when sanding doesn’t immediately clog up the fine filter like it used to do prior to adding the cyclone.
The only planed changed to this set up is a change of impeller & motor assembly, at the moment it is a 2kw motor & I have been give a 3kw assembly though before I change it I’m going to run some tests on air flow through both units to see if altering it will give any noticeable improvement.
Good luck with yours it really is a good idea to minimise the dust in the workshop & even if you only add a fine filter it will be well worth it.

 

[SLM]

Thanks Doug,

That’s not a million miles away from my thinking…

The question remains whether or not to get rid of one bag/filter. The cross sectional area of the rectangular section ducting of my extractor is 18,600mm2, versus 12272mm2 for the 125mm pipes. So I’m currently struggling to get my head around the reduction of airflow suggested by Brian, with the removal of the Y-branch. Perhaps some tests are called for.

 

[Doug B]

I know what you mean, but if my math is right the three inlets on the extractor in your picture have a area of 23561mm2 so how does that figure against the 18600mm2 after it
I looked at it that by altering things I might not get the suction I once had but it would still have suction, it wasn’t like it wouldn’t suck at all & as long as it was good enough to clear the machines that’s all I needed & it does.

 

[SLM]

I know what you mean, but if my math is right the three inlets on the extractor in your picture have a area of 23561mm2 so how does that figure against the 18600mm2 after it
I looked at it that by altering things I might not get the suction I once had but it would still have suction, it wasn’t like it wouldn’t suck at all & as long as it was good enough to clear the machines that’s all I needed & it does.

Ah, but as I said, I’m only attaching one machine, directly to the 125mm inlet; we can ignore the 3 100mm inlets.

 

[Doug71]

I used to have a double bag extractor similar to your picture. Initially it never worked properly as nearly all the shavings went into one bag but hardly any into the other. After a bit of research I found there was a kind of fin in the Y section which needed bending slightly to even up the airflow. If yours is a similar design you might be able to block off one side and bend the fin to direct all the shavings to the other side as a test.

My current extractor is a Jet single bag which can supposedly take two 4" pipes or one 6". I used just one 4" initially but thought I would upgrade to 6" after getting the advice it would be better. I bought all the 6" pipe and fittings etc but it didn't work well, some shavings from my PT just got left in the pipe. I haven't got around to trying it yet but I think the sweet spot would be a 5" pipe as that is the size that joins the fan to the collector on mine.

 

[Yojevol]

When you say the air flow is reduced, do you mean by the removal of the Y-shaped duct, or by the reduction in surface area of the final filter?

Thanks for you input.

Reduction of filter area. The filter pressure will probably go up slightly and therefore push a bit more through the remaining bag. If you're going to fit a paper filter the flow is going to change anyway. It would be worth blanking off one filter now to see if there's any obvious reaction.
Brian

 

[Inspector]

Doug B before changing to a bigger motor measure the impeller and make sure it is bigger too. Most of the 2hp single bag/cartridge DCs have a 12"/300mm impeller. Many of the 3hp 2 bag/cartridge DC's have the same 12"/300mm impeller. The extra airflow from them is because of the second filter. If the impeller of the "new" one is 13"/330mm or a touch bigger there will be much better flow. No point in changing if the impeller is the same.

Duct/hose diameter is the limiting factor with a HVLP DC. The surface area of the walls to the duct area ratio is higher in a small duct and self limits the flow because of the wall drag. A 4"/100mm flows about 400CFM/680m3/hr, a 5"/125mm flows about 800CFM/1360m3/hr and a 6"/150mm flows 1200 CFM/2040m3/hr. Hose has about 3 times the drag as the same length of smooth duct so keep the use of hose to a minimum. If using ducts that are too small the flow is choked even if using a big DC.

Reducing filter area reduces the flow. If you want to reduce the footprint stack 2 or more filters if you have the ceiling height. Problem with that is you can't use the Chinese paddle filters, you'll have to get industrial filters and either use air to blow the dust out or add a shaker. ClearVue in the US is selling a shaker setup and would be one to imitate. Amazon as I suspect others sell the same kind of vibrating motors for a lot less. Amazon.co.uk

A couple places in the UK for industrial filters. Specify the air flows from inside to outside if getting them made. Industrial filters flow from outside to inside. They are cheaper than the Asian made paddle ones too.

https://c-airfiltration.co.uk/dust-cartridge-filters
https://www.djnuk.co.uk
Pete

 

[SLM]

Reduction of filter area. The filter pressure will probably go up slightly and therefore push a bit more through the remaining bag. If you're going to fit a paper filter the flow is going to change anyway. It would be worth blanking off one filter now to see if there's any obvious reaction.
Brian

Thanks Brian,

Logically, I thought that must be the case, but as I said, I defer to greater experience, knowledge and understanding of these things!

As you say, a little testing will not go amiss.

Doug B before changing to a bigger motor measure the impeller and make sure it is bigger too. Most of the 2hp single bag/cartridge DCs have a 12"/300mm impeller. Many of the 3hp 2 bag/cartridge DC's have the same 12"/300mm impeller. The extra airflow from them is because of the second filter. If the impeller of the "new" one is 13"/330mm or a touch bigger there will be much better flow. No point in changing if the impeller is the same.

Duct/hose diameter is the limiting factor with a HVLP DC. The surface area of the walls to the duct area ratio is higher in a small duct and self limits the flow because of the wall drag. A 4"/100mm flows about 400CFM/680m3/hr, a 5"/125mm flows about 800CFM/1360m3/hr and a 6"/150mm flows 1200 CFM/2040m3/hr. Hose has about 3 times the drag as the same length of smooth duct so keep the use of hose to a minimum. If using ducts that are too small the flow is choked even if using a big DC.

Reducing filter area reduces the flow. If you want to reduce the footprint stack 2 or more filters if you have the ceiling height. Problem with that is you can't use the Chinese paddle filters, you'll have to get industrial filters and either use air to blow the dust out or add a shaker. ClearVue in the US is selling a shaker setup and would be one to imitate. Amazon as I suspect others sell the same kind of vibrating motors for a lot less. Amazon.co.uk

A couple places in the UK for industrial filters. Specify the air flows from inside to outside if getting them made. Industrial filters flow from outside to inside. They are cheaper than the Asian made paddle ones too.

https://c-airfiltration.co.uk/dust-cartridge-filters
https://www.djnuk.co.uk
Pete

thanks Pete,

That’s all helping the thought process. I had wondered about stacking filters. It may come down to reviewing the available space, and deciding which configuration works best.

 

[Inspector]

You could take a page from industrial dust filtration and mount the filters horizontally so they wouldn't be as tall.
https://www.aqcdust.com/dust-collec...horizontal-compact-cartridge-dust-collectors/
Pete