Going from NO DC to Oneida SDG . ductwork plan check.

[joel cervera]

Been looking at the calculator on Bill Pentz's site. I have a question I haven't quite seen answered on my forum search. Most threads deal with having sufficient CFM But FPM seems to get brought up less. I have now been planning an 8" main ( same size as inlet on cyclone) with 6" drops. With regard to sufficient FPM ( to keep dust from collecting in ducting) Bill shoots for 4000FPM w/ 1000 cfm required at furthest tool port.
He shows a table with calculated FPM. It shows that 6" Ducting keeps the FPM above the 4k FPM target. 7" is just under target. And 8 shows low. This seems to indicate to that an 8 ducting may not be ideal? 7 or six are better in this respect. My s.p at the furthest tool shows about 6 based on what I've calculated. So sufficient cfm with my system looks good.
But with respect to FPM should I neck down the 8" inlet on my cyclone to a 7 or 6 inch main? Or will the 6 inch drops keep FPM in the mains from dropping too low. Trying to understand this and any help is appreciated.

Thanks and below is the chart from Bills calc.


Screen Shot 2018-02-15 at 11.41.00 AM.png

[Jim Becker]

Oneida designs the inlet size that is appropriate for a given cyclone model. The only benefit, IMHO, to reducing at that point is, perhaps a small cost benefit for duct work materials. My Oneida cyclone has a 7" inlet and I ran that to the first major branch and only then dropped to 6" for the main beyond that point. For the single woodworker, your proposal to use an 8" main with 6" drops is reasonable because you'll only be using one tool at a time. The performance should be great. For the size of your shop, there's little benefit to getting too deep in the weeds over these calculations. It would be a different story for a very large shop, particularly with multiple simultaneous users. Again...my opinion which isn't always worth the ones and zeros it's printed on.

[Bill Dufour]

I would raise the dc up so the inlet is as high as possible. I think I would cut a hole in the ceiling for the motor.

[Jim Becker]

I would raise the dc up so the inlet is as high as possible. I think I would cut a hole in the ceiling for the motor.

I agree with this.

[Joe Jensen]

Been looking at the calculator on Bill Pentz's site. I have a question I haven't quite seen answered on my forum search. Most threads deal with having sufficient CFM But FPM seems to get brought up less. I have now been planning an 8" main ( same size as inlet on cyclone) with 6" drops. With regard to sufficient FPM ( to keep dust from collecting in ducting) Bill shoots for 4000FPM w/ 1000 cfm required at furthest tool port.
He shows a table with calculated FPM. It shows that 6" Ducting keeps the FPM above the 4k FPM target. 7" is just under target. And 8 shows low. This seems to indicate to that an 8 ducting may not be ideal? 7 or six are better in this respect. My s.p at the furthest tool shows about 6 based on what I've calculated. So sufficient cfm with my system looks good.
But with respect to FPM should I neck down the 8" inlet on my cyclone to a 7 or 6 inch main? Or will the 6 inch drops keep FPM in the mains from dropping too low. Trying to understand this and any help is appreciated.

Thanks and below is the chart from Bills calc.


Screen Shot 2018-02-15 at 11.41.00 AM.png

The smallest opening in a run nearly completely determines the CFM that a collector can pull. This is almost always the port on the machine. The port size is like 95% of the driver of CFM. Going to a larger and larger pipe will have a very tiny effect on CFM. Bill's calculator is great, but you need to determine the actual port size where the air is pulled from near the blade. Take my Felder sliding table saw. It has a 5" port on the side that connects to a 4" flex hose that connects to the cast iron blade shroud under the blade. That opening has the same area as a 3.5" round port. So in Bill's spreadsheet I load the 3.5" and not the 5" on the side of the machine. When you do this you will see that changing from 6" to 8" pipe won't make a difference. But you will see that the velocity in feet per minute will be way too low in the 8" duct and you may not get enough velocity in a 6" vertical run to lift the dust. Very carefully measure the smallest opening for each machine and fill in Bill's sheet that way.

[Carl Kona]

Joel,

There is another end of the spectrum you should consider when thinking about 8" main, that is the required CFM at the 4000FPM in an 8" duct. As you go larger, your required CFM to maintain the same FPM will also rise dramatically (probably why the LOW reading). If you look in the attached chart you will see that from 6" to 8" you are almost doubling the required CFM at the same 4000 FPM. Looking at the 3HP Gorilla fan curve you would have to be under 5" of SP to produce that level of CFM. With a 7" main you would need 1066CFM (or 8" of SP) and a 6" main needs 784 CFM (or ~10" of SP). So you will have to do a little trial and error to determine your best setup.

As Joe mentioned above, consider the other end is the tool opening and what restriction that will place on your system. I can't recall who did the test but it was very informative regarding port size and hose size and length. He did several combinations of 4-6" ports/hoses and lengths and as you would assume the largest size (duct and hose) going right to the tool with the largest opening (some were enlarged), delivered the best performance.

BTW 6" of SP sounds on the low side when you start with almost 4.5" of SP of cyclone, filter, overhead, etc. What 'CFM Required' are you using at the top? Your SP varies with that CFM level.
Duct data chart.JPG

[Rod Sheridan]

Joel,



BTW 6" of SP sounds on the low side when you start with almost 4.5" of SP of cyclone, filter, overhead, etc. What 'CFM Required' are you using at the top? Your SP varies with that CFM level.
Duct data chart.JPG

Hi Carl, you do not add the cyclone and filter when using a packaged unit like the Oneida cyclone.

Oneida produce the unit curve with the cyclone and filter installed.

If you were using a bare blower, you would add the cyclone and filter...........Regards, Rod.

[Carl Kona]

Rod,

When I look at the Oneida curve I see 1510CFM @1.8" SP, which is stated to include the filter. So if someone determines they have 4" of static pressure in there shop ducting (less cyclone and filter) they have to add it to the 1.8" to get 5.8" correct? I don't think a lot of people start from the first data point but simply look at the 4" point and look across at the corresponding CFM. Since most independent tests I have seen show the manufacturer tests to be close if not slightly optimistic, using Bill's numbers would give a final result that should easily be met.

As a general rule wouldn't using the spreadsheet number be similar without having to find the first system data point and doing the math from there? If I missed something please let me know.

Thanks,
Carl

[Rod Sheridan]

Hi Carl, no the 1510 CFM @ 1.8"SP is the rating for airflow at that pressure.

So if you connected ducting to the system that would result in 1.8"SP, you would have 1510 CFM.

If you have 4" SP you look at the graph for 4" and read your airflow.............Regards, Rod.

[Jacob Mac]

I agree with this.

What does raising the DC inlet as high as possible do?

[Jim Becker]

What does raising the DC inlet as high as possible do?

Eliminates or reduces any bends near the cyclone inlet since most folks hang their duct at or near ceiling height.

[Carl Kona]

Hi Carl, no the 1510 CFM @ 1.8"SP is the rating for airflow at that pressure.

So if you connected ducting to the system that would result in 1.8"SP, you would have 1510 CFM.

If you have 4" SP you look at the graph for 4" and read your airflow.............Regards, Rod.

Rod,

I am confused. I understand that 1.8" is what is measured at that CFM but isn't that the pressure drop of the cyclone? Why wouldn't they measure at 1" or 1/2" and get a higher CFM to advertise? I have some Dwyer equipment and following their instructions I attach a 6"x60" duct to the 6" inlet of my cyclone and measure velocity and static pressure. So when I measure 2" of pressure with only this test duct connected, isn't that pressure drop across the cyclone? If I eliminated the cyclone and just attached the duct to the blower wouldn't the measured pressure be that of the duct and be much lower?

Carl

[joel cervera]

BTW 6" of SP sounds on the low side when you start with almost 4.5" of SP of cyclone, filter, overhead, etc. What 'CFM Required' are you using at the top? Your SP varies with that CFM level.
Duct data chart.JPG

Thanks for the input Carl. As Rod stated.. The Bill Pentz calculator also states that if one is looking at a cyclone who's fan curve says something like S.P. at inlet then factors such as the cyclone, filter, etc have been accounted for and need not be added again. The fan curve for oneida cyclones do fall into this. Aside from the ducting and fittings the only other factor included to my s.p. is general overhead at 2.0.

[David L Morse]

..I am confused. I understand that 1.8" is what is measured at that CFM but isn't that the pressure drop of the cyclone? Why wouldn't they measure at 1" or 1/2" and get a higher CFM to advertise? ...l

The 1.8" measurement is the pressure drop of the test duct with no restrictions. A test duct has an entrance and so it has entrance loss. A round duct will have an entrance loss of about 1.2 (bell mouth) to 1.9 (plain end) times the velocity pressure in the duct. 1500 CFM in 8" is 4300 fpm, giving a velocity pressure of 1.1" wg. Depending on the shape of the entrance you would expect a static pressure loss of 1.3 to 2.1" wg at that flow rate.

.. So when I measure 2" of pressure with only this test duct connected, isn't that pressure drop across the cyclone? If I eliminated the cyclone and just attached the duct to the blower wouldn't the measured pressure be that of the duct and be much lower?..

To measure the pressure drop across the cyclone you would have to measure the pressure difference between the actual outlet of the cyclone and it's inlet. That is, add a pressure port at the entrance to the fan or near the top of the cyclone outlet tube. That could require a bit of surgery on some units.

If you were to remove the cyclone the total system resistance would go down, the flow would go up and the pressure drop across the test pipe would go up. The pressure measured at the DC inlet would be more negative, that is, a bigger number. I don't know if you call that lower or higher.

[Carl Kona]

The 1.8" measurement is the pressure drop of the test duct with no restrictions. A test duct has an entrance and so it has entrance loss. A round duct will have an entrance loss of about 1.2 (bell mouth) to 1.9 (plain end) times the velocity pressure in the duct. 1500 CFM in 8" is 4300 fpm, giving a velocity pressure of 1.1" wg. Depending on the shape of the entrance you would expect a static pressure loss of 1.3 to 2.1" wg at that flow rate.

Thanks for that David. I never paid attention to how significant the entry loss is on a plain end duct. When I measured my unit and it was about 2" with an unrestricted test duct (which matched Bill's assumption of ~2" for his cyclone) I figured I was right the right ballpark. But you are correct I need to measure between the blower and cyclone and not the room pressure as a baseline.

My mistake was going back to what someone told me about fan curves and that they will never change, it is just the SP you add to the fan and where you land on the curve. But this reminded me that is false. Through manufactures fan/system curves and my own testing I found the fan curve can change significantly depending on the changes to the inlet/outlet of the fan/blower (like adding a cyclone). The curve to consider must be created where your ducting begins.

I guess this is why manufactures put 7 & 8" inlets on 1.5 & 2 HP cyclones, to get better fan curves. Not because someone will put a 7" main on a 1.5HP cyclone.

Thanks again,

Carl