what happens to CFM when dust extractor is hooked up to 2 1/2" port or 2 1/2" hose?

[Cory filder]

what happens to CFM when dust extractor is hooked up to 2 1/2" port or 2 1/2" hose? Trying to determine if a dust extractor is a good replacement for my dead shopvac. I want to use it for a bandsaw and strip sander inside an enclosure. my old shop vac did the job well. I also want to use it for smaller tools in the future. I would like to stay at 2 1/2" if possible

my understanding is most
extractors ~150 cfm, 95-100 inch lift ~1 1/2" hose
shop vac ~150 cfm, 55 in lift ~ 2 1/2" hose.

if I put an adapter on the extractor, what happens to the CFM?

[Jim Becker]

Performance suffers. Why? Small ports need high static pressure (vacuum) to move enough air through them to do the job. Dust collectors, on the other hand, work purely by moving a large volume of air at a given high velocity, but at low static pressure. The moving air is what transports the dust and chips. Small ports cannot supply the volume of air that a DC typically requires to work well. Even a 4" port is not really large enough, despite it being the defacto-standard on most North American designed woodworking tools. A 4" duct/hose cannot support more than about 450 CFM tops. A 2" hose/port is less than half of that. Small tools, both stationary like you describe and hand-held do best with a shop vac/extractor for dust collection while tools with 4" ports or larger do best with a dust collector designed for the purpose. You cannot go by the CFM figures on the vac because it's a high pressure (suction) system.

There are a few (not inexpensive) systems on the market that are designed to support both small port/low CFM/high vacuum and large port/high CFM/low vacuum applications. Oneida's SuperCell is an example of that.

[Cory filder]

Performance suffers. Why? Small ports need high static pressure (vacuum) to move enough air through them to do the job. Dust collectors, on the other hand, work purely by moving a large volume of air at a given high velocity, but at low static pressure. The moving air is what transports the dust and chips. Small ports cannot supply the volume of air that a DC typically requires to work well. Even a 4" port is not really large enough, despite it being the defacto-standard on most North American designed woodworking tools. A 4" duct/hose cannot support more than about 450 CFM tops. A 2" hose/port is less than half of that. Small tools, both stationary like you describe and hand-held do best with a shop vac/extractor for dust collection while tools with 4" ports or larger do best with a dust collector designed for the purpose. You cannot go by the CFM figures on the vac because it's a high pressure (suction) system.

A point of clarification. dust extractors typically come with 1 1/2" hose. I'm looking to convert this to a larger 2 1/2" hose, not a smaller one. this is the opposite situation of a dust collector (4"-6") going down to a 2 1/2.

[Jim Becker]

A point of clarification. dust extractors typically come with 1 1/2" hose. I'm looking to convert this to a larger 2 1/2" hose, not a smaller one. this is the opposite situation of a dust collector (4"-6") going down to a 2 1/2.

My Festool extractor fully supports a 3.5"/36mm hose. So does every other shop vac I've owned. I actually use that size hose for general cleanup...an orange, Ridgid branded hose that is very flexible and durable.

[George Yetka]

Even a 4" port is not really large enough, despite it being the defacto-standard on most North American designed woodworking tools.

To this end I usually have an empty blastgate wide open on my DC. But I believe Cory is looking at putting a larger hose on an extractor like a CT as apposed to replacing it with another Shop vac.

Cory Im pretty sure if you open it up that much you will have a harder time moving dust. It would be like using a garden hose to drink a water out of a cup it may work but not as effectively as the right size straw.

[George Yetka]

My Festool extractor fully supports a 3.5"/36mm hose. So does every other shop vac I've owned. I actually use that size hose for general cleanup...an orange, Ridgid branded hose that is very flexible and durable.

Jim I think the biggest they make is the 50mm hose which is 1.9685"

Cory If you ran this 50mm hose and upsized at the machines I think you would be better off then if you upsized at the extractor. This would keep static high.

[George Yetka]

Cory The key to extractors is Static pressure. DCs like CFM

[Cory filder]

My Festool extractor fully supports a 3.5"/36mm hose. So does every other shop vac I've owned. I actually use that size hose for general cleanup...an orange, Ridgid branded hose that is very flexible and durable.

is that a 3.5" or 36mm.I think there was a typo there. This is good. I just didn't want to purchase something expensive without knowing for sure.

Cory The key to extractors is Static pressure. DCs like CFM

I would just love to see if anybody has some CFM data source to verify what happens

[Jim Becker]

I may have misspoke on the exact hose size, but the Extractor will take the largest shop vac hose typical on the market and in the case of Festool, it's the same inlet size as both of my small Rigid vacs that I use for cleanup.

As to CFM data, like George says, it's not material with Extractors/vacs as they work on "suction" primarily, not CFM.

[Carl Beckett]

A thought:

'too large' of a hose cross section for a given flow rate means the velocity of air inside the hose is low.

Particles have a pseudo 'buoyancy' that needs to happen to carry them along the hose. (the small particles are buoyant, but the large particles can drop out)

So I am not convinced larger dia duct work is always the best answer for dust collection efficiency. I would suggest there may be minimum velocities to maintain. Yes too small means fluidic loss as it travels through the length and pressure differential is lost (lower flow rates). But imagine a 20" dia duct - it would not achieve high enough velocities to be effective either.

Specific to your question - doubling the dia of the hose might roughly be 4 times the cross section > 1/4th the velocity. If you were only sanding the small particles might stay suspended sufficiently for that to work. But larger pieces might settle in the hose. A bandsaw and strip sander should produce relatively smaller particles - I would expect it to work fine. (no hard data to back that up, just a gut guess)

[Bill Howatt]

A thought:

'too large' of a hose cross section for a given flow rate means the velocity of air inside the hose is low.

Particles have a pseudo 'buoyancy' that needs to happen to carry them along the hose. (the small particles are buoyant, but the large particles can drop out)

...

And this is why islands form at the mouth of fast flowing rivers - where the velocity drops because the channel is wider.

[Aaron Inami]

I may have misspoke on the exact hose size, but the Extractor will take the largest shop vac hose typical on the market and in the case of Festool, it's the same inlet size as both of my small Rigid vacs that I use for cleanup.

As to CFM data, like George says, it's not material with Extractors/vacs as they work on "suction" primarily, not CFM.

I don't think this is accurate. I have the Festool dust extractor, which allows up to a 50mm (1.96") hose. Your smaller Rigid vacs may take the same hose, but I had a large Shopvac where the hose was actually too big to fit onto the Festool. So the hose outlets are not all the same size.

As far as CFM, look through this review. They do an excellent series of tests on a variety of dust extractors. Their CFM and suction tests show results for both an "empty bag" and a "full/dirty bag":
https://www.toolboxbuzz.com/head-to-...-head-to-head/

On this review, be aware that the Makita dust extractor that performed so well is the previous version. The current Makita model (VC4210L) does not perform nearly as good - it is about the same as the Milwaukee. I believe these suffer in performance due to having two individual filter sections that the air has to pass through before the exhaust.

[Aaron Inami]

what happens to CFM when dust extractor is hooked up to 2 1/2" port or 2 1/2" hose? Trying to determine if a dust extractor is a good replacement for my dead shopvac. I want to use it for a bandsaw and strip sander inside an enclosure. my old shop vac did the job well. I also want to use it for smaller tools in the future. I would like to stay at 2 1/2" if possible

my understanding is most
extractors ~150 cfm, 95-100 inch lift ~1 1/2" hose
shop vac ~150 cfm, 55 in lift ~ 2 1/2" hose.

if I put an adapter on the extractor, what happens to the CFM?

The CFM for dust extractors (i.e. ~150 CFM) is rated at the turbine itself with no hose attached. As soon as you put on a 1-1/2" or a 2" (i.e. 50mm) hose, your actual CFM will be significantly lower. That being said, the primary reasons for getting a dust extractor is the higher suction performance and the ability to adjust or turn down the suction. Also, some dust extractors can be quieter than a normal shopvac. Smaller tools like random orbit sander will actually perform better with less suction.

If you want to use this for a bandsaw and strip sander, then a larger shopvac with the 2-1/2" will have much better collection over any normal dust extractor. However, the shopvac is a one speed high speed solution that just won't work as well with the random orbit sander (or any other smaller tool that you need to reduce suction).

[Aaron Inami]

A thought:

'too large' of a hose cross section for a given flow rate means the velocity of air inside the hose is low.

Particles have a pseudo 'buoyancy' that needs to happen to carry them along the hose. (the small particles are buoyant, but the large particles can drop out)

So I am not convinced larger dia duct work is always the best answer for dust collection efficiency. I would suggest there may be minimum velocities to maintain. Yes too small means fluidic loss as it travels through the length and pressure differential is lost (lower flow rates). But imagine a 20" dia duct - it would not achieve high enough velocities to be effective either.

Specific to your question - doubling the dia of the hose might roughly be 4 times the cross section > 1/4th the velocity. If you were only sanding the small particles might stay suspended sufficiently for that to work. But larger pieces might settle in the hose. A bandsaw and strip sander should produce relatively smaller particles - I would expect it to work fine. (no hard data to back that up, just a gut guess)

Hi Carl. This is definitely true when looking at traditional high volume dust collectors where your duct is in the 6", 8" or larger range. On these systems, the duct can be too large where it actually slows down the air velocity and you will not have enough lift to pull dust up a vertical duct or enough velocity to move the dust through a horizontal duct. This is more critical on a horizontal duct where the dust may fall and start to build up. This creates a fire hazard.

However, this scenario does not apply to the dust extractor / shopvac systems. On these, the suction and air velocity is such a high amount that you won't have the problem with "not being able to move dust through the hose".

[George Yetka]

The CFM for dust extractors (i.e. ~150 CFM) is rated at the turbine itself with no hose attached. As soon as you put on a 1-1/2" or a 2" (i.e. 50mm) hose, your actual CFM will be significantly lower. That being said, the primary reasons for getting a dust extractor is the higher suction performance and the ability to adjust or turn down the suction. Also, some dust extractors can be quieter than a normal shopvac. Smaller tools like random orbit sander will actually perform better with less suction.

If you want to use this for a bandsaw and strip sander, then a larger shopvac with the 2-1/2" will have much better collection over any normal dust extractor. However, the shopvac is a one speed high speed solution that just won't work as well with the random orbit sander (or any other smaller tool that you need to reduce suction).

I watched a video yesterday showing that Straight pvc had little to no loss on an extractor/shop vac velocity. Where as a single 10' piece of corrugated hose even held straight cut 1/3 of the velocity. Hopefully this info helps