I found the Festool unit leaks a lot at the rectangular seal to the chip container, and hence looses suction. My solution was to use a plastic collection bag, not so much for the chips, but to extend outside the unit and provide a better seal around the perimeter. It is generally true that it is difficult to get a Festool product to suck.
I am a degreed chemical engineer and have over 50 years working as such. One issue we face all the time is a material balance on a system. Whatever goes in comes out and at steady state the mass rate is equal. Now as pressures change within the flow path the actual volumetric rate is a function of the density at that point, and most significantly changes with pressure, ignoring temperature affects. You are measuring the linear rate in the open so you are measuring essentially the standard volumetric flow regardless of the size of the nozzle inlet. I would say the cross sectional area is that of the measuring device and that will give you the ACFM through the meter and if the air is nominally standard atmosphere and temperature you are measuring standard cubic feet per minute (SCFM) And regardless of the hose size, the SCFM is constant in the system equal to what goes in. This is due to the mass rate at any point in the system being constant because there is no accumulation of any mass within. So the difference is that the hoses and inlet/outlet ports add resistance in the flow path and your total throughput is reduced when the resistance increases. In theory if you measure the inlet and outlet linear rates they should be the same assuming the air exiting has had time to expand to atmospheric conditions before passing though the meter. The only other gotcha is that you cannot assure that the full area of the meter is seeing the airstream so multiplying by the meter area is not a given but assuming it is, you should have equality. Your calculation using an orifice area is probably not valid since you are not measuring the flow rate at the conditions within and as I noted, only the meter area calculation is likely close. If you really wanted to know the actual volume flow a volume flow positive displacement gas gage would likely be required as this would present numbers based on volumes without assumptions as to conversion from linear to volumes which needs a valid cross-section area.
This test gives same results when testing the FESTOOL cyclonique CT CT-VA-20e with this Oneida, and they were vacuum real wood dust. So while your engineer analysis might be correct on the theory, it won’t change anything to the fact this really works and way better then anything else on the market. Just look for other videos.
Good info @ importance to pay attention to static charge buildup toward end of video. Thanks - I’ll be sure to review the more detailed info on the Oneida website to learn the finer details on how to NOT let static charge build up and thereby fry my tools.
Haha, the way you have that initial shot set up, I was thinking these were large machines sitting on the floor a ways back behind you. Then you touched the one behind you and shattered the illusion!
If you build up static electricity and get a massive discharge it hits you that maybe there's something wrong with grounding. Doesn't take much but boy you get the message. Nice review on the CFM percentage lasses each one has even with the 2 inch diameter hoses.
I’ve seen a lot of anemometer tests on dust collectors and there’s a huge problem with all of them. A vacuum pulls air from all directions towards the inlet, so a smaller inlet will pull more air towards the back of the anemometer than one that is closer in diameter to the anemometer. These tests should really be done with a shroud/adapter that only allows air to be pulled through the front of the device.
Yes I agree - holding a small diameter hose against a large diameter anemometer is not an accurate way to measure. Wood Whisperer did the same thing and I think it gives bad readings.
cool review.. perfect timing. I just got a Festool CT-48 E AC HEPA yesterday!
I found the Festool unit leaks a lot at the rectangular seal to the chip container, and hence looses suction. My solution was to use a plastic collection bag, not so much for the chips, but to extend outside the unit and provide a better seal around the perimeter. It is generally true that it is difficult to get a Festool product to suck.
I am a degreed chemical engineer and have over 50 years working as such. One issue we face all the time is a material balance on a system. Whatever goes in comes out and at steady state the mass rate is equal. Now as pressures change within the flow path the actual volumetric rate is a function of the density at that point, and most significantly changes with pressure, ignoring temperature affects. You are measuring the linear rate in the open so you are measuring essentially the standard volumetric flow regardless of the size of the nozzle inlet. I would say the cross sectional area is that of the measuring device and that will give you the ACFM through the meter and if the air is nominally standard atmosphere and temperature you are measuring standard cubic feet per minute (SCFM) And regardless of the hose size, the SCFM is constant in the system equal to what goes in. This is due to the mass rate at any point in the system being constant because there is no accumulation of any mass within. So the difference is that the hoses and inlet/outlet ports add resistance in the flow path and your total throughput is reduced when the resistance increases. In theory if you measure the inlet and outlet linear rates they should be the same assuming the air exiting has had time to expand to atmospheric conditions before passing though the meter. The only other gotcha is that you cannot assure that the full area of the meter is seeing the airstream so multiplying by the meter area is not a given but assuming it is, you should have equality. Your calculation using an orifice area is probably not valid since you are not measuring the flow rate at the conditions within and as I noted, only the meter area calculation is likely close. If you really wanted to know the actual volume flow a volume flow positive displacement gas gage would likely be required as this would present numbers based on volumes without assumptions as to conversion from linear to volumes which needs a valid cross-section area.
You knew that. Right Donavan??
This test gives same results when testing the FESTOOL cyclonique CT CT-VA-20e with this Oneida, and they were vacuum real wood dust. So while your engineer analysis might be correct on the theory, it won’t change anything to the fact this really works and way better then anything else on the market. Just look for other videos.
Good info @ importance to pay attention to static charge buildup toward end of video. Thanks - I’ll be sure to review the more detailed info on the Oneida website to learn the finer details on how to NOT let static charge build up and thereby fry my tools.
Haha, the way you have that initial shot set up, I was thinking these were large machines sitting on the floor a ways back behind you. Then you touched the one behind you and shattered the illusion!
Very informative Donavan.
If you build up static electricity and get a massive discharge it hits you that maybe there's something wrong with grounding. Doesn't take much but boy you get the message. Nice review on the CFM percentage lasses each one has even with the 2 inch diameter hoses.
What is the height of the dust deputy with the hose on top?
I’ve seen a lot of anemometer tests on dust collectors and there’s a huge problem with all of them. A vacuum pulls air from all directions towards the inlet, so a smaller inlet will pull more air towards the back of the anemometer than one that is closer in diameter to the anemometer. These tests should really be done with a shroud/adapter that only allows air to be pulled through the front of the device.
Yes I agree - holding a small diameter hose against a large diameter anemometer is not an accurate way to measure. Wood Whisperer did the same thing and I think it gives bad readings.