It’s been awhile since I played around with how the Variac voltage controller affected airflow using the Huky 500 exhaust fan. It was finally time for the final leg of this journey. The smaller 2000-00 series Dwyer Magnehelic gauge ended up pinning the needle, the next one up came from Ebay (2000-0 0-.50”water column).
I found some black plastic plugs on Amazon to start with, and really intended to stop there. Except for scoring a used perforated Huky drum off Ebay, which required taking the roaster apart. Might as well try making the vacuum connection permanent 🙂
Using the above method was able to re-connect the J-Pipe running the silicon hose thru the drop door and to the Dwyer Magnehelic. On the below graph, it’s referenced as C-“WC or Capped inch water column.
This was pretty tricky to do, as the stainless is quite hard. I bought an inexpensive tap/drill set in the beginning, the drill kept skipping around; a small pilot hole solved that issue. It was done on a small tabletop drill press resting the neck on a block of wood. I struggled with the tap, only to find out it was not up to the task. The HSS 1/8” NPT version was able to cut the threads. Unfortunately the tap handle would only turn 90* before bumping into the flat plate; lots of flipping, reversing. Slow going but it ended up working.
Now I’m able to compare Anemometer and negative pressure readings using the Variac voltage regulator under different conditions. And a big plus from this experiment shows the Huky damper is quite capable of controlling air flow using a Magnehelic gauge.
The headings are: Variac Volts, C-capped J-pipe, 2000-0 Magnehelic, 2000-00 Magnehelic, Anemometer M/S, repeat 2000-0 gauge, repeat 2000-00 gauge, w/335g roasted coffee. All done with the Huky running with an empty perforated drum.
| Volts | C-“WC | 0-“WC | 00-“WC | M/S | 0-“WC | 00-“WC | 335g | |||
| 120v | .45” | 17.2 | .42” | |||||||
| 95v | .50” | .40” | 16 | .37” | ||||||
| 90v | .48” | .38” | 15.6 | .35” | ||||||
| 80v | .44 | .36” | 14.2” | .33” | ||||||
| 75v | .40” | .30” | 13.8” | .31” | ||||||
| 70v | .37” | .27” | .24” | 12.6 | .28” | .23” | .35” | |||
| 65v | .32” | .24” | .21” | 12.2 | .25” | .21” | .32” | |||
| 60v | .27” | .19” | .19” | 10.6 | .22” | .18” | .28” | |||
| 55v | .24” | .16” | .16” | 9.6 | .19” | .15” | .23” | |||
| 50v | .17” | .12” | .12” | 8.5 | .16” | .12” | .16” | |||
| 45v | .14” | .10” | .10” | 7.5 | .12” | .09” | .10” | |||
| 40v | .10” | .06” | .07” | 6.5 | .09” | .07” | .08” | |||
| 35v | .07” | .04” | .04” | 4.8 | .06” | .05” | .06” | |||
| 30v | .05” | .03” | .03” | 3.7 | .04” | .03” | .04” | |||
| 25v | .03” | .01” | .02” | 2.5 | .03” | .02” | .02” | |||
| 20v | .02” | 0 | .01” | 1.0 | .01” | .01” | .01” |
There was another test done using 335g of roasted coffee starting with 70v and tapering down. The results were similar the the “pipe plug” capped test. It’s possible the vacuum readings might change again while roasting green coffee with the burner running.
How does all this work, one might ask?
The Dwyer 2000-0 has some oscillation, it being a used unit not sure if the issue is with the gauge or the fan. Dwyer 2000-00 has a smoother swing, again it is used as well. On the test with roasted beans in the drum 70v topped off at .35” wc, above the .25” maximum on Dwyer’s 2000-00. Being this testing is brand new, I’ll have to start using the Magnehelic during an actual roast to see how the airflow affects the gauges range.
Changing the voltage on the variac causes a slight rpm delay with the Huky’s centrifugal fan. I don’t see this as an issue, however the damper works faster making quick air flow changes using the Magnehelic as a guide. This brings up some interesting questions, how does roasting on the Huky compare between damper/Magnehelic vs Variac/Magnehelic? Variac has plenty of advantages; noise and ease of adjustments are a few.
hankua 