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5. Refer to Figure 2. Use the exhaust gas velocity
determined in step 4 and find the exhaust gas
velocity value in thousands on the bottom scale.
Move vertically up until this value intersects the
curve of the corresponding silencer type as
determined in step 1. Move left on the horizontal
axis and determine the back pressure drop value in
kPa (in. of Hg).
Note: Refer to Figure 3 to calculate in inches of
water and feet per minute.
kPa
in. of Hg
6.4
1.9
6.1
1.8
5.8
1.7
5.4
1.6
5.1
1.5
4.7
1.4
4.4
1.3
4.1
1.2
3.7
1.1
Pressure
3.4
1.0
Drop
3.0
0.9
2.7
0.8
2.4
0.7
2.0
0.6
1.7
0.5
1.4
0.4
1.0
0.3
0.7
0.2
0.3
0.1
Note: When figuring the silencer pressure drop for side inlet, add 0.75 kPa
Figure 2 Silencer Back Pressure Drop (in. of Hg)
56 Appendix
0
0.3
0.6
0.9
1.2
1.5
0
1
2
3
4
5
Exhaust Gas Velocity in Thousands
A = Hospital Silencer
B = Critical Silencer
C = Residential Silencer
D = Industrial Silencer
(0.25 in. of mercury or 3.4 in. of water) to the back pressure.
Example:
(10100 ft./min.) intersects with critical silencer
curve B and the corresponding back pressure
value is approximately 2.8 kPa (0.85 in. of
mercury). Silencer type is end inlet from step 3
information with no additional back pressure drop
value per the following note.
1.8
2.1
2.4
2.7
3.1
3.4
6
7
8
9
10
11
Exhaust
velocity,
A
B
C
D
(m/min.)
3.6
4.0
4.3
5.8
4.9
12
13
14
15
16
(ft./min.)
3075
m/min.
TP-6609 6/08
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