Thread: Clearing the air

At the moment, I'm thinking of putting the DE outside and venting directly to the air. I live in a rural area and my nearest neighbor is 500m away. The shed only has single phase power and it is a rental, so getting three-phase connected isn't practical.

Do you mean removing the filters and letting the sawdust blow where it will?

Originally Posted by BobL

Do you mean removing the filters and letting the sawdust blow where it will?

If it is feasible to do it I guess yes. That is one thing I've found a bit confusing from the Pentz site. From what I've read I think that with a good cyclone little dust would blow outside. With a regular DE is this practical?


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Originally Posted by arniew

If it is feasible to do it I guess yes. That is one thing I've found a bit confusing from the Pentz site. From what I've read I think that with a good cyclone little dust would blow outside. With a regular DE is this practical?

Well it would works far better than cyclone because cyclones like filters still generates a back pressure that restricts flow.
However it only works in a rural situation because it creates an out an out visual mess and on a day with no breeze you are going to be surrounded by a cloud of sawdust

Instead of a cyclone you could setup a low resistance separator.
Most separators including most cyclones significantly impact on the flow so given you have the space what would work would be a large container like an old large (the bigger the better) rainwater tank - it doesn't matter if it is full of leaks, in fact it has to leak lots because you want minimal resistance.
If the pathway out of the tank is >10x the cross sectional area of the ducting you use the air speed will drop at least by the same amount - at that speed most of the big bits of sawdust will drop out of the air flow and fall into the tank. It will still let all the very fine dust out of the system but you won't see much of it and it will be rapidly diluted into the air.

If you have spare water you could install misting sprinkler inside the tank that would damp the finer dust down - it would probably harden and grown a mould. Could make for interesting compost.

Originally Posted by BobL

Well it would works far better than cyclone because cyclones like filters still generates a back pressure that restricts flow.
However it only works in a rural situation because it creates an out an out visual mess and on a day with no breeze you are going to be surrounded by a cloud of sawdust

Instead of a cyclone you could setup a low resistance separator.
Most separators including most cyclones significantly impact on the flow so given you have the space what would work would be a large container like an old large (the bigger the better) rainwater tank - it doesn't matter if it is full of leaks, in fact it has to leak lots because you want minimal resistance.
If the pathway out of the tank is >10x the cross sectional area of the ducting you use the air speed will drop at least by the same amount - at that speed most of the big bits of sawdust will drop out of the air flow and fall into the tank. It will still let all the very fine dust out of the system but you won't see much of it and it will be rapidly diluted into the air.

If you have spare water you could install a sprinkler inside the tank that would damp the finer dust down - it would probably harden and grown a mould. Could make for interesting compost.

Thanks Bob, that's a great idea. We have an old tank lying in the right spot already. [emoji106]

Is the 3HP unit with 12" impeller suitable?


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Originally Posted by arniew

Thanks Bob, that's a great idea. We have an old tank lying in the right spot already. [emoji106]

Well there you go!

Is the 3HP unit with 12" impeller suitable?

Impeller size is on the small size but it will be good enough to test out the system.

The build is now under way.

First job was to strip back the DE to just the impellor and motor housing.

Thankfully the inlet was 6", so the 3x 4" adaptor was removed.

A new mounting system was put in place and then the impellor/motor part was hoisted into place high up on the shed wall. It will vent outside into an old water tank, and the 6" trunk line will hang from the metal roofing frame. Getting this in place was the hardest so far. It is heavy and took a hoist, a guide line and two people to get it in the right spot.

Next bit is to start on the blast gates. More reading to do on that one.

IMG_0458.jpgIMG_0459.jpgIMG_0460.jpgIMG_0461.jpg

I'd be looking to add a BMH to that impeller, the inlet is a square ended 6" so a BNH will really help it move more air.

The inset photos below show how Bueller did on his.
Arniew.jpg

Originally Posted by BobL

I'd be looking to add a BMH to that impeller, the inlet is a square ended 6" so a BNH will really help it move more air.

The inset photos below show how Bueller did on his.
Arniew.jpg

Thanks Bob, I hadn't seen this mod. I'm planning on building your BMH jig so will make this change.

Any thoughts on the impeller out? It is rectangular and almost the area of a 6" pipe.


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Originally Posted by arniew

Thanks Bob, I hadn't seen this mod. I'm planning on building your BMH jig so will make this change.

Good I'm looking forward to seeing someone else give this a go.

Any thoughts on the impeller out? It is rectangular and almost the area of a 6" pipe.

I know the one, If you can enlarge it then do so but I think it will be quite tricky to do.

Originally Posted by BobL

Good I'm looking forward to seeing someone else give this a go.



I know the one, If you can enlarge it then do so but I think it will be quite tricky to do.

Yes, it will be tricky. I'll have to mull over it. Too many other parts to distract me for the moment.

I'll let you know how I go making BMHs


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Its not that difficult. I used the large jointing end from a 6" pipe, heated it and shaped it around a rectangular inside and outside mould.

IMG_0521.jpg

I then made a wooden collar to match the rectangular outlet on the housing and routed a recess to take the pipe.

IMG_0588.jpg

No restrictions in the throat and 6" pipe fits straight on the outlet (shown lower in the picture)

Frankly, venting DCs outside with standard 30-micron filters is exactly how the originals were designed to work before our small shop vendors foolishly brought these back inside and added fine filters. The under 30-micron sized particles are what we call airborne dust and this stuff when vented outside vanishes with no visible trace, plus breaks down as soon as it gets moist. You are not really going to move enough air with that 12" diameter impeller or with your 6" ducting to get more than about 785 CFM. We need a real 1000 CFM to have good fine dust collection which requires at least a 14" DC impeller or 15"+ cyclone impeller. So, based on your setup what would be best would be to simply put your DC outside in its own covered area where the air does not blow back into your shop plus add a strong fan that blows out of one side of your shop with window or door open on the other side to get a good flow through.

Thanks Lappa and Bill for your helpful comments.


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So, based on your setup what would be best would be to simply put your DC outside in its own covered area where the air does not blow back into your shop plus add a strong fan that blows out of one side of your shop with window or door open on the other side to get a good flow through.

The best place to vent the air out of a workshop is "at the roof line". When fine dust that escapes collection is made, it is slightly warmer than the surrounding air and as it behaves like warm air and rides on warm air currents it will rise to the roofline. This is why so much fine dust gets onto rafters. When venting inlets and outlets are at or near ground level, especially in large high sheds it is possible that escaped fine dust will sit in that space and only slowly be removed by sedimentation. If ventilation extraction is turned off after dust making activities any remaining fine dust at the roofline will rain down onto the rest of the shed. In Australia roofline venting also helps to keep shed cool.