Thread: 3 hp DC

A couple of "Cut to the chase" comments.

My shed is 10 by 12 m. Machines include 24 inch thicknesser, 18 inch TS and wood lathe. If the dusty can handle these it will cope with everything else.

A 3HP is too small for this size of shed. You will really need a 4 or preferably 5HP setup with a 15 or 16" impeller for that size shed.

Plan to locate the dusty outside the shed.

This is the single best thing you can do for dust extraction.

Please note that most commercial cyclones impose a significant restriction on the flow of air.
So while they keep filters clean or even, if located outside, eliminate the need for filters they may rob more flow than dirty filters impose on them.

Only the newer designs like the Clearvue provide a low restriction flow but even they start at 4HP and 15" impeller for a small shed and in your case I would be looking seriously at the Clearview Max which has a 16" impeller.

That's a pretty large space with large equipment. It soundsounds like budget isn't a deal breaker and thus I would recommend just going straight for the Clearview. That way you'll only buy once and be happy.

Thanks Bob / Dom. Despite doing a search before posting this thread, after posting I found a post of Bob's from yesterday answering most of my questions. As a matter of interest, how would a 5 hp second hand dust bag type machine work.


Dom, If I feel I have to buy a clearview then that's what I will get. None the less I need to be able to convince myself (then my wife) that the cheaper options aren't adequate. The difference in cost between a second hand machine and a clearview represents a lot of other toys forgone. My large gear is old and has been accumulated over a number of years. The combined cost would not be a lot more than a clearview.

Thanks
Tony

Originally Posted by tony_A

Thanks Bob / Dom. Despite doing a search before posting this thread, after posting I found a post of Bob's from yesterday answering most of my questions. As a matter of interest, how would a 5 hp second hand dust bag type machine work.

Dom, If I feel I have to buy a clearview then that's what I will get. None the less I need to be able to convince myself (then my wife) that the cheaper options aren't adequate. The difference in cost between a second hand machine and a clearview represents a lot of other toys forgone. My large gear is old and has been accumulated over a number of years. The combined cost would not be a lot more than a clear view.

A well setup ClearVue, even under heavy dust making operations is almost "set and forget" and empty the bin every now and then .

Cleaning the filters on big filters units is most unpleasant especially if it has to be done often which happens under heavy dust making operations.
The max flow rate for bigger DCs is determined more or less by the size of the ducting and how well the machines can breathe.
The flow rates for a Clearvue remain the same more or less until the waste bing fills
On filtered units the flow rate will decline over time - do you really want to be stopping to clean filters so you can keep dust free inside a shed.

The bag options are more tolerable to small operations/sheds/machinery like mine (in the last couple of years I have only empty my bags on average about every 3 months) but your thicknesser and TS will fill even a filter bag unit faster than you can say "dust, cough cough . . . ."

On such a big shed I'd be seriously considering a 9" trunk line(s) and 6" down drops to all machines.
If you use PVC ducting, the fixed cost of ducting / junctions / flexy and gates will sett you back about the same amount as a ClearVue
If you want to go galv I hope you have a fat cheque book.
This means the fraction difference in the total cost between the "ducting + bagged unit" and "ducting + Clearvue" does not look so bad.

It frustrates me that the automatic response seems to be to get a Clearvue. The first questions should always be how much air movement does each machine require, and what length and diameter of ducting is there to each machine and how many are run together. If you don't know how much air volume is needed and what the losses are, how can you know what you need? A Clearvue could just be an expensive way of not getting enough airflow, if you don't do the sums.

Originally Posted by richmond68

A Clearvue could just be an expensive way of not getting enough airflow, if you don't do the sums.

I suppose the default answer is Clearview because I'm unaware of any other system short of an industrial unit that is suitable and available in Australia and that would flow more air. Aside from maybe a Felder RL250 which is a LOT more expensive again. No one is suggesting that the ducting runs and machine layout shouldnt also be adequately designed to also suit the system. I'm just not sure what point it is you are making? Do you believe there is a better system available for the money? As for "enough airflow" I believe that there is no right answer to this and the default should always be "as much as possible" within the financial constraints of the user.

On this page on BP's site there is info on air flow requirements for machinery.
The table is about 2/3rds half way down the page - it's copyrighted so I won't reproduce it here.
Dust Collection Research - Dust Collection Basics

The same table is also posted here
Improving machine cabinet dust ports

There are 4 sets of flows provided
Chip collection - orange column
OHSA - pink column - this is based on a unresearched northern hemisphere standards of 1ppm for hardwoods and 5 ppm for softwoods. It makes no allowance for the added toxicity of our timbers and the particle size distribution of the dust being generated
ACGIH Standards - Yellow column, is a US Industrial hygienist standard. Takes some particle size info into account
Euro Standard - Green column. These are recommended standards for European wood workers. Anyone worried about allergies should work at this level.

Flow rates for the bigger machines are in the 900 to 1100 CFm range which is why BP recommends 1000 CFM at source.

The OP has a 24" thicknesser and a 18" TS which means he will need more than 1000 CFM at source. For those size machines I would be targeting something like 1200- 1400 CFM

For a 10 x 20 m shed, placing a DC outside the shed in the middle of a longer wall there will be ducting runs >10 m.
A 3HP will struggle to achieve 1000 let alone 12-1400 CFM on the end of a 10+m duct especially if the choked nature of machinery and blocked filter bags are considered.
This puts us in the next league of machinery.

For the OP - it is highly unlikely that a bigger better DC will solve the problem unless the air breathing capacity of machinery itself is taken into account.
It's no use running 9 and 6" ducting to a machine and hooking these up to a 4" dust port. The small ports will have to be opened up to full 6" and a large pathway for air to enter a machine provided.
For ideas on how to do this take a look at this thread
Improving machine cabinet dust ports

Originally Posted by DomAU

I'm just not sure what point it is you are making? Do you believe there is a better system available for the money? As for "enough airflow" I believe that there is no right answer to this and the default should always be "as much as possible" within the financial constraints of the user.

The point I thought was pretty clear, you need to know how much capacity is needed. In the case of a 24" thicknesser, consider the volume of chips they produce. Even at the low end they can generate the equivalent of a shredded 8x4 sheet of 9mm ply per minute. It's not a matter of a better system for the money, it's ensuring you get something up to the task.

There's no reason to ignore industrial units if you've got the 3 phase capacity to run them and the space to put them. 4 bag units with 7.5kw motors turn up on the used market quite often as they're frequently used as dedicated collectors with cnc or edgebanders in commercial shops. That's really the minimum I'd want to use in a shop the size of the OP's with that machinery for central collection.

I didn't need to do the following calculation because I have done similar ones a few times before so I knew the Clearvue CVMAx was up for it.

A basic requirement to move stuff like sawdust is a 2:1 air to sawdust weight ratio,

A 1.2 x 2.4 x 9 mm sheet of ply should weigh about 12 kg.

To move that much dust requires at least 24 kg of air.

A ClearVue Max moves 1800 CFM in an 8" duct.
BTW Despite claims to the contrary a 7.5 kW 4 bag unit won't actually move much more than this through an 8" duct, to do that it will have to go to a 10" duct.
The reason for using such big units is usually to cope more with multiple machines operating simultaneously.
As the OP didn't mention this then I assume he was a lone operator.

Back to the sums

1800 CFM =61kg/min of air which puts us a >5:1 ratio.
The spare 3:1 ratio over and above the 2:1 to move the sawdust is critical in capturing the fine dust and it should do this OK

The other requirement is that the air has to be moving at 4000 FPM otherwise the sawdust will drop out of suspension.
1800 CFM in an 8" duct is 5261 FPM so all good there.

One issue we have not considered is that 8"ducting is very hard to get in PVC so one tends to go to 9" PVC.
This puts the air speed at 4074 FPM which is close to borderline although 4000 FPM is considered a very conservative value and in practice the CVmax seems to be able to cope with 9" ducting.
EG at the mens shed we're using 9" trunk line and a CVmax, usually with 2 or more small machines running at the same time and have not had any problems with sawdust dropout in the trunk line.

This calculation assumes the thicknesser will allow 1800 CFM through its internals to collect the dust in the first place.
This is rarely the case and why its common to throw ever increasing amounts of blower HP at the problem with limited success.
Simple things like air inlet ports often don't even exist on these machine and where air outer ports are provided they tend to be on the small side.
This issue affects any dust collector that would be connected - my point here is that folks are quick to blame the DC whereas they should be looking at the machine

About the only machine likely (if rarely) to be found in a DIY shed where a CVMax will struggle in servicing is something like a 1.2m wide sander.

And no bag/filter cleaning is needed at any stage.
Why anyone would go for a bagged unit for these size of machines is beyond me.
Filtered units are good for blokes like me with small machines and who only empty their bags on a ~3 monthly basis.

Bob when you said you can't get 8" PVC and have to go to 9" I looked at what I can get here and all the larger size pipes for all the different schedule equivalents jump in 2" increments, 4" to 6" to 8" to 10" et cetera. Oddities of how our counties evolved I suppose. So given the choice I should get 8" for a CV-Max and not 10"? Shop is 7.5 x 8.5 meter with the CV-Max in the middle of the short wall and the pipe intended to run around the perimeter left and right from the DC. A pair of half loops looking like [*]. I don't want piping running across the shop blocking light and eating up headroom for swinging and flipping wood. Usually one person working, me , occasionally 2, woodworking including bowel turning.

Thanks
Pete

Pete, the PVC Bob refers to in Aust has an ID of 225mm and an OD of 250mm. If that sounds like a high wall thickness it's because it's used for under road drainage. Not sure how they spec the sizes in your neck of the woods, but stick to the ID measures.

Originally Posted by QC Inspector

So given the choice I should get 8" for a CV-Max and not 10"? Shop is 7.5 x 8.5 meter with the CV-Max in the middle of the short wall and the pipe intended to run around the perimeter left and right from the DC. A pair of half loops looking like [*]. I don't want piping running across the shop blocking light and eating up headroom for swinging and flipping wood. Usually one person working, me , occasionally 2, woodworking including bowel turning.

I'd go with 8" if you can get it. It can easily handle two machines.

At 10" the CVMax Air Speed is nominally 3447 FPM which is below the 4000 FPM threshold.

Pete, the PVC Bob refers to in Aust has an ID of 225mm and an OD of 250mm. If that sounds like a high wall thickness it's because it's used for under road drainage. Not sure how they spec the sizes in your neck of the woods, but stick to the ID measures.

The 9" pipe I''m referring to has an ID of 240 mm and a wall thickness of 4.5 mm so it s is 249 mm OD.
See PVC PIPE - STORMWATER PIPE - Pipe Online - Retic Fittings , Plumbing Fittings, Reticulation Supplies supplied Australia wide
The nominal air speed for this pipe on a CVMax calculates out at 3700 FPM but at as I said before, 4000 FPM is a nominal conservative figure because it still seems to work with this ducting at the mens shed.

I have done some sawdust fall out tests with 4" ducting and the nominal max air flow in this pipe with a DC is ~425 CFM or 4870 FPM.
It's tricky to determine an exact speed at which problems start because fallout is very dependent on chip size and shape (surface area to volume ratio) and the sawdust to air ratio. Small mounts fine dust and large curls are transported even as low as 1000 FPM (<100 CFM).
All of what I would call sawdust including large chips was able to be transported at 2000 FPM, but some larger piece of wood did not move even at 4000 FPM.

There are actually two things to consider - one is maintaining the air flow so the dust doesn't fall out of suspension, the the other is being able to pick sawdust up off the bottom of the duct after it has fallen out of suspension. This can happen if the filters clog, someone turns off a DC before the dust is cleared on a long duct run, a power failure, a blockage of some kind etc.

Remember the air speed at the boundary wall will be much slower than 4000 FPM
With the 4" ducting the nominal speed needed to pick up the dust that had deposited was about 20% more than the slowest speed that induced a fall out. Once again sawdust shape played a role, curlies protruding up into the faster air near the middle of the pipe were easily picked up by faster air speeds that were just above drop out speed. OTOH mm size chips definitely needed the 20% increase in air speed. Running curlies through a duct containing fallen out chips also helped sweep up the fallen out dust.

When I dismantled my old 4" system I did notice a layer of fine dust up to 10 mm thick had formed in a couple of the long runs. This had caked into a sort of crust that no air DC air speed would remove.
This dust may have fallen out when the filters blocked. Whatever was in the sawdust plus a bit of air humidity probably sort of glued it together. I have also seen this in another system.

Enough rambling for now.

Thanks to all. Have ended up with some very detailed answers to my original question. While I use my machines a bit more than Bob I would still consider a cheap used bagged unit if I could be sure it had the air flow capacity that he details above. Can't be confident of this without a performance curve for the fan.

Bob, What type of pvc ducting did you use in the men's shed.

Tony

Originally Posted by tony_A

Thanks to all. Have ended up with some very detailed answers to my original question. While I use my machines a bit more than Bob I would still consider a cheap used bagged unit if I could be sure it had the air flow capacity that he details above. Can't be confident of this without a performance curve for the fan.

You will need a 5HP/15" or better impeller.
You must be prepared to modify machinery to get the necessary air flows.

Bob, What type of pvc ducting did you use in the men's shed.

Stormwater ducting - see link above.