Airflow measurements

[Schreck]

Last month I made some airflow measurements when I changed the bag under my dust collector.  It is a 1994 vintage Penn State DC-2 with a 1.5 HP motor; the blower has a 10.5" impeller, 6" inlet and 5" outlet.  I removed the original spiral ramp when I installed the Thien baffle last summer.  The baffle is ¼" masonite, sold for use as a whiteboard.  Since there is no cone in the ring, I added a ¾" plywood ceiling with a large coffee can chimney.  The can is 6" diameter and extended about halfway from the ceiling to the baffle. 

[Schreck]

First I measured the airflow with a 10' section of 5" steel duct, using a 6" to 5" reducer.  All subsequent measurements were made with a 10' section of 6" steel duct. Measurements were made 54" from the open end of the duct with a pitot tube and a digital manometer.  Motor measurements were made with a kW meter. 

Changing from a 5" to a 6" duct did not increase the airflow.  Next I removed the filter and the airflow increased slightly.  The filter is oversized and un-seasoned, so this made sense.  Next, I removed the baffle and ceiling altogether, installed a new bag, the filter and tested the airflow, which almost doubled. 

My baffle was causing a 50% drop in airflow, so before I put it back together, I decided to increase the chimney diameter to 8".  This improved airflow quite a bit lowering the impact of the baffle to a 33% drop versus the dust collector without a baffle. 

[Schreck]

This table shows some of the motor measurements, and the relationship between watts amps and power factor is worth reviewing.  As AC motors become unloaded, the power factor drops, so if all you can measure is amps, be aware that the change in airflow is greater than the change of amps indicates.

[retired2]

Nice work Schreck.  While your setup is slightly different than mine, the results are amazingly similar.  As I recall my separator created a 40%, drop in airflow.

[phil (admin)]

Did you measure with the baffle but without the chimney?  The baffle alone shouldn't cause a tremendous hit to CFM on a SS ring adaptation.  The chimney will, though.

However, the chimney will help with separation quite a bit.

The old "no free lunches" saying applies.

[Schreck]

Did you measure with the baffle but without the chimney?  The baffle alone shouldn't cause a tremendous hit to CFM on a SS ring adaptation.  The chimney will, though.

However, the chimney will help with separation quite a bit.

No, but I will, maybe with the plywood opening rounded over to ease the exiting airflow.  Given the plywood ceiling, my rig is more like a top hat than a typical ring adaptation.  But you're right - it's all about the ceiling/chimney.