Vacuum on Low

[w802h]

I'm curious how many cfm a Festool vacuum pulls when it's turned all the way down. 

 

[Holmz]

You could measure it about 3 different ways I can think of.

 

[w802h]

My vacuum doesn't have that feature.  I'm trying to understand the suction range on Festool vacuums a bit better to decide if it's a worthwhile purchasing.  Thanks. 

 

[Holmz]

Other sanders do not need to have the suction turned down, which adds more options.

 

[w802h]

Holmz, what three ways would you use to measure it?  I was kind of hoping that Festool would provide a number by posting in the Ask Festool area.  I agree that both sander and sanding medium matter as well. 

 

[grbmds]

What is the reason you would need to reduce the suction of the vac other than to use it with a Festool sander? I don't think that I've ever encountered any other power tools where I'd want to use anything but the highest setting on the vac.

 

[Holmz]

Holmz, what three ways would you use to measure it?  I was kind of hoping that Festool would provide a number by posting in the Ask Festool area.  I agree that both sander and sanding medium matter as well.

I am sure that they could answer it and they would likely use #1 below.

1) (Direct air velocity measurement)
Use an anemometer like a kestral, then multiply the m/s by the square meters of area. You could also do pressure drop versus flow this way.
(Or Take a piece of plastic and mask off most of a room where the plastic is like an accordion. Hook up the vacuum to the plastic and see how long it takes for the plastic to rest against the other wall.)

3) (Derived velocity measurement)
Measure the velocity of the air using doppler shift and speed of sound, or do it using time delay.

4) One could measure the pressure change in a room, which would be measuring the derivative of the volume change, which is the same as the flow rate, and it is an instantaneous measurement.

There are certainly more, if I stroke the beard a while longer.
I like the idea of a big pipe and blowing smoke in and then timing how long ittakes to move.

 

[TylerC]

As far as we know, this isn't something that we've measured. We've reached out to the team in Germany to see if they can track down a number for you.

 

[GarryMartin]

I have a cheap digital anemometer off eBay and just put in on my 36mm hose at the end of the boom arm on my CTL 26E.

It was off the scale on full suction, and registered 31.5 m/s on low. I'm not sure of all the mathematics behind this, but punching that number into an online calculator gives about 68CFM - does that sound about right? I'm sure it's much more complicated than that, and is affected by the filter, how full the bag is, the length of hose, the fact that it goes from 36mm to 50mm etc., but I hope that helps in the meantime.

[attachimg=1]

 

[w802h]

Garry,

Thanks for going above and beyond!  It sounds like "low" is about half the max.  This is a lot less than the vacuum I currently use.  Thanks.

 

[Holmz]

I have a cheap digital anemometer off eBay and just put in on my 36mm hose at the end of the boom arm on my CTL 26E.

It was off the scale on full suction, and registered 31.5 m/s on low. I'm not sure of all the mathematics behind this, but punching that number into an online calculator gives about 68CFM - does that sound about right? I'm sure it's much more complicated than that, and is affected by the filter, how full the bag is, the length of hose, the fact that it goes from 36mm to 50mm etc., but I hope that helps in the meantime.

[attachimg=1]

good work Garry.
The flow is pressure drop related.
Using some wider duct that the hose goes into wit lower the velocity to allow the max to be measureable... So maybe a 4" or larger PCV tube. You need enought length for the flow to be relatively laminar.
Good job on it - you got that minmum number.