John Henderson
TVWBB Fan
I know every one of you has been wondering it as you set the dampers on your WSM - the area of the opening is not linear with the rotation of the disk. If I want to set the openings to 1/3, for example, how far do I rotate the disk? It's not 1/3 of the way from the closed to open position.
Now you do not have to wonder any more.
a = 2/pi*(arccos(1 - f) - (1 - f)*sqrt(f*(2 - f)))
where "a" is the fraction of total area that is open (0 - 1), and "f" is the fraction of the rotation from fully closed to fully open (0 - 1).
In graph form, the relationship is:
The x-axis is "f" and y-axis is "a."
Some common settings:
a = 0, f = 0.
a = 1/4 (25%), f = 36.5%
a = 1/3 (33.3%), f = 44.7%
a = 1/2 (50%), f = 59.5%
a = 2/3 (66.7%), f = 73.5%
a = 3/4 (75%), f = 80.2%
a = 1 (100%), f = 100.0%
Now, I expect someone to create scales we can mount next to the damper disc with an arrow on the disk so we can set the area accurately.
Now you do not have to wonder any more.
a = 2/pi*(arccos(1 - f) - (1 - f)*sqrt(f*(2 - f)))
where "a" is the fraction of total area that is open (0 - 1), and "f" is the fraction of the rotation from fully closed to fully open (0 - 1).
In graph form, the relationship is:
The x-axis is "f" and y-axis is "a."
Some common settings:
a = 0, f = 0.
a = 1/4 (25%), f = 36.5%
a = 1/3 (33.3%), f = 44.7%
a = 1/2 (50%), f = 59.5%
a = 2/3 (66.7%), f = 73.5%
a = 3/4 (75%), f = 80.2%
a = 1 (100%), f = 100.0%
Now, I expect someone to create scales we can mount next to the damper disc with an arrow on the disk so we can set the area accurately.
