Thread: dust extration

Originally Posted by John T

This maybe a question for BOB L I want to install a new system of dust extraction, my question is it better to have one 6" run of 25mtrs or2 x 4" pipes of the same distance with 4"flex of 1.6mtrs from 6 machines with blast gates on every machine, I think the dusty has 1900 cfm witch is the best option regards john t.

A 1900 CFM dusty sounds like a 3HP DC.
There is no chance of it ever moving 1900 CFM in any sort of real situation as the manufacturers "industry standard test" is physically incorrect and do not take into account any filters/bags/ducting/junctions/cyclones.

Connected to a standard 3HP DC a short length (a couple of metres) of 4" ducting can carry no more than about 420 CFM.
The same length of 6" ducting is limited to 1260 CFM
So you see it actually takes 3 lengths of 4" ducting to carry about the same amount of air as a 6" duct.

However 25m of ducting is vastly different than a couple of metres and really impacts on air flow of any diameter pipe

According to Bill Pentz StaticCalc Program 25 m (83ft) of 4" ducting will generate 6" of Water Columm static pressure resistance to move air at 400 CFM of air
Since a 8HP DC only only generates at the very most about 10" of total pressure this leaves only 4" of pressure to drive actual air.
The result is a reduced flow so this reduce the back pressure, and by repeating the calculation several times we end up with a flow rate of around 320 CFM

This does not take into account filters/bags/junctions/ machinery. By the time that is take into account then the flow will be well below 300 CFM and maybe around 250 CFM
The 6" ducting will be around 3 times that.

In other words both are pretty bad considering you really need 1000 CFM to remove fine dust.

For distances over about 6m the only way to move air so that the ducting resistance does not impact the flow is to use 8" or 9" ducting.
However you need to be careful using that as small DCs cannot generate the air flow and hence air speed needed to keep sawdust in suspension and the pipe will clog.

You can of course make your own large rectangular cross section ducting using something like MDF.

Thanks bob L,
It looks a thow we need to go to a 5hp dusty to move the amount of air needed. thank for your input john t

Originally Posted by BobL

A 1900 CFM dusty sounds like a 3HP DC.
There is no chance of it ever moving 1900 CFM in any sort of real situation as the manufacturers "industry standard test" is physically incorrect and do not take into account any filters/bags/ducting/junctions/cyclones.

Connected to a standard 3HP DC a short length (a couple of metres) of 4" ducting can carry no more than about 420 CFM.
The same length of 6" ducting is limited to 1260 CFM
So you see it actually takes 3 lengths of 4" ducting to carry about the same amount of air as a 6" duct.

However 25m of ducting is vastly different than a couple of metres and really impacts on air flow of any diameter pipe

According to Bill Pentz StaticCalc Program 25 m (83ft) of 4" ducting will generate 6" of Water Columm static pressure resistance to move air at 400 CFM of air
Since a 8HP DC only only generates at the very most about 10" of total pressure this leaves only 4" of pressure to drive actual air.
The result is a reduced flow so this reduce the back pressure, and by repeating the calculation several times we end up with a flow rate of around 320 CFM

This does not take into account filters/bags/junctions/ machinery. By the time that is take into account then the flow will be well below 300 CFM and maybe around 250 CFM
The 6" ducting will be around 3 times that.

In other words both are pretty bad considering you really need 1000 CFM to remove fine dust.

For distances over about 6m the only way to move air so that the ducting resistance does not impact the flow is to use 8" or 9" ducting.
However you need to be careful using that as small DCs cannot generate the air flow and hence air speed needed to keep sawdust in suspension and the pipe will clog.

You can of course make your own large rectangular cross section ducting using something like MDF.

Hi Folks. I have been reading through the reams of very illuminating threads on Dust Extraction contained in this site over the last few months (...my head hurts!!) and have been very impressed by, and thankful of, the very good advice I've been able to glean from my readings.

There is a comment by BobL in the above post that I have a query about

.....But first, my situation. I am about to move into a new house with a decent sized workshop (in the basement) and, taking into account all of my readings, had virtually decided to replace my existing CT 3hp dusty with a CV1800 (with filters - long story but the basement location means that direct external venting is extremely problematic), 6" ducting to my machines, improved ports on the machines etc etc. However, in looking at location of machinery I will need ducting runs of up to 10 metres including the drop down to the machines (eg 6 mtr to combo saw/ thicknesser / jointer, 6 mtr to drop saw, 9 mtr to drum sander, 10 mtr to lathe, 8 mtr to bandsaw and router table). Each machine would be served by ducting branching off the main line with blast gates as close as possible to the branch point.

So my question in view of BobL's comment above is, will my duct lengths impede the performance of the CV1800 to the extent that I should consider the CV max instead?

I would really appreciate any comment. Cheers, Jakor.

Originally Posted by Jakor

Hi Folks. I have been reading through the reams of very illuminating threads on Dust Extraction contained in this site over the last few months (...my head hurts!!) and have been very impressed by, and thankful of, the very good advice I've been able to glean from my readings.

There is a comment by BobL in the above post that I have a query about

.....But first, my situation. I am about to move into a new house with a decent sized workshop (in the basement) and, taking into account all of my readings, had virtually decided to replace my existing CT 3hp dusty with a CV1800 (with filters - long story but the basement location means that direct external venting is extremely problematic), 6" ducting to my machines, improved ports on the machines etc etc. However, in looking at location of machinery I will need ducting runs of up to 10 metres including the drop down to the machines (eg 6 mtr to combo saw/ thicknesser / jointer, 6 mtr to drop saw, 9 mtr to drum sander, 10 mtr to lathe, 8 mtr to bandsaw and router table). Each machine would be served by ducting branching off the main line with blast gates as close as possible to the branch point.

So my question in view of BobL's comment above is, will my duct lengths impede the performance of the CV1800 to the extent that I should consider the CV max instead?

I would really appreciate any comment. Cheers, Jakor.

My understanding is that the max is designed for a situation where multiple machines AND a trunk line of at least 8" diameter are in use.
It won't pull significantly more air if just 6" ducting is used all the way.

The max will pull significantly more air than the 1800 from a single machine if 8" or greater ducting is used all the way to each machine. The problem now is that no machine is set up to take 6" ducting let alone 8" ducting.

If you can afford the cost of the amen and the 8 or 9" ducting I would buy the max and run an 8" trunk down the length of the shed and then use 6" drop downs to the machines.
You can always uses 2 x 6" drop downs on some machines but the machines must be modified to accept the 6" ducting.