There is a useful table of measured air rates on various examples of African
ethnographic bellows types in H. Friede and R. Steel, "Traditional wooden drum
bellows of south-western Africa", South African Archaeological Bulletin
41:12-16, 1986. The measurement method was by velometer.
A. Zulu bag bellows (presumably with valve - article doesn't say!) attached to
implala horn nozzle.
Pumping rate (105-120 strokes per minute). Cross-sectional area of nozzle 175 sq
mm Air velocity 24 meters/sec; air output 254 litres/minute.
B.Tswana bag bellows with interchangeable ox-horn nozzle (2 trails with
different nozzles).
Trial 1: rate 140; area 227; velocity 25; output 340
Trial 2: rate 140; area 154; velocity 30; output 277
C. Ovambo double drum bellows (a single carved unit comprising two separate
chambers, each with integral carved wooden nozzle; skin diaphragms with stick
attached to center; valveless; both chambers operated simultaneously by single
standing bellows operator).
Right chamber:
Trial 1: rate 160; area 254; velocity 16.5; output 251
Trial 2: rate 264; area 254; velocity 12.5; output 191
Left chamber:
Trial 1 rate 128; area 254; velocity 12; output 183.
The authors comment that "an interesting feature of the drum bellows became
evident during the tests. If pumping speed was increased from 160 to 264 strokes
per minute, the air volume delivered from the bellows decreased considerably -
an effect probably resulting from disturbance of the equilibrium in the partial
vacuum/air pressure sustem prevailing in the long narrow-bore airducts at very
high pumping speeds".
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