Engineering Bulletin

119
Engineering Data
821, 831, 92 Series,
98VOH, H and V Series
Drop Chart, Use with
size selection charts
Instructions for use
of Drop Chart
The drop of the air stream is
determined by using the throw and
velocity of the register selected. On
the drop chart, lay a straight edge
connecting these values. The total
drop of the air stream will be the
sum of the drop due to temperature
(D
t
) and the drop due to spread
(D
s
).
Example: The drop for a 92 Series
register “C” deflection 16x5 size has
an 800 fpm velocity and a 16 foot
throw. Connect these two points
on the chart and read the drops as
follows:
D
t
= 2.7’ D
s
= 2’
D total = 2.7 + 2 = 4.7’
D
t
= Drop along line of
throw due to temperature
difference.
D
s
= Drop resulting from
vertical spread.
Engineering Data