Here's the pressure/flow effect of the BC-1-MD in inches of Water Column for the full range of damper settings (0 to 100 by 10s) at room temperature and operating temperature (400F) with the fan full-on.

Very usable range and effect from 0 to 70, then maxed out after that. I recall Hank (I think it was) mentioning that these fans on the smaller roasters are rated for larger roasters, so this makes sense. My Dave Borton - Mill City airflow by lighter flame-bending approach video for low, medium, and high notional airflow settings had me at 0, 30, and 60, so this is also a pretty good testament to that approach's effectiveness.

Here's another curve added of the fan through it's range of settings with the damper left at full open.

Note these old fans really gave poor control, which is why the damper helps if you don't change your fan like Josh (Madman13) did.

I think I may set my fan to 60 and redo the damper curve next go-around since there is no sense in running the fan past its usefulness only to likely wear it out sooner. It's really odd that you can hear the fan increasing speed between 60 and 100 making you think it is doing something but this shows it is doing nothing in terms of airflow.

Outstanding graphs, great presentation of the data. I'm sure anyone with a BC-1 and no magnehelic gauge will appreciate this.

I observed the same thing with the electrical control of the fan and my magnehelic.. really not much control there although I agree that the sound of the fan would have you believe otherwise. The manual damper seems to do a pretty good job of giving good control throughout the fan's useable range.

Good Job!
The Dwyer 0-0.25" is a perfect fit. I've bought three used gauges and had good luck with all of them. And you may get a little different reading while roasting. I think the air pressure gauge helps visualize the air flow settings, help make a small adjustment, and indicate a backdraft or other outside effect on the air pressure.

You are aware, i assume, that flow is proportional to the square root of the pressure drop . Your variation of flow is much less than pressure. To change flow by 2 you would change pressure by 4x. Applies to heat/gas pressure as well. This is why you can buy square root gauges.

This subject came up in the old Huky forum relating to gas pressure vs heat; and the explanation ended up being way too scientific. A more simplified approach would really be helpful in understanding the relationships.

I'm curious where you are tapping off this pressure. I recently picked up a North TJ-067 and very interested in measuring airflow with similar approach.

Edit: I just searched and I think I found the source of this testing. The tap is on the bean chute. Yes?
Buckeye BC-1 Deconstructed

Yes, on the bean chute. I took it off to see how the flow goes through and there is a plate that separates between the bean chute and exhaust chute. I stuck it just before the restriction begins as this should be where the highest relative pressure exists.

Mbb wrote:You are aware, i assume, that flow is proportional to the square root of the pressure drop . Your variation of flow is much less than pressure. To change flow by 2 you would change pressure by 4x. Applies to heat/gas pressure as well. This is why you can buy square root gauges.

Yes, and the velocity changes with area and there are several area changes through the roaster with probably the biggest being from the drum to the chute. Flow meters that I am familiar with (limited knowledge) must be associated with a specific area and temperature so I'm not sure how you would easily configure one as an add-on to a roaster. Did you have something in mind that you could share?

I also believe that flow should be viewed in a relative sense and I think most other roasters would as well. I don't think the absolute flow values are meaningful to most. You could take the square root of those pressure values and the curve would still have a similar shape but the ordinate values would change. In fact the pressure increases by about 5x so the flow increases by 2.24x, but I don't know that it matters much.

EddyQ wrote:I'm curious where you are tapping off this pressure. I recently picked up a North TJ-067 and very interested in measuring airflow with similar approach.

Edit: I just searched and I think I found the source of this testing. The tap is on the bean chute. Yes?
Buckeye BC-1 Deconstructed

I would pop out the ET analogue thermometer and put it there at first. That's what I did with my Feima 800n which had a 1/4" npt thread socket, before drilling and tapping the other side.