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2.5 Piping
Note: Select piping with a diameter that is the same size
as or larger than the manifold outlet's inside
diameter.
D
Keep exhaust lines as short and straight as possible.
D
Use schedule 40 black-iron pipe.
D
Use sweep elbows with a radius of at least three times
the pipe diameter.
D
Use exhaust piping that conforms to applicable
codes.
D
Support the exhaust piping securely, allowing for
thermal expansion.
D
Insulate the exhaust piping with high-temperature
insulation to reduce the heat rejected by exhaust
piping and consequently the amount of ventilating air
required.
Exhaust temperatures measured at the engine's
exhaust outlet are listed on the generator set
specification sheets.
Route the exhaust piping a minimum of 914 mm (36 in.)
from combustible material, including building materials
and natural surroundings.
When planning exhaust silencer and piping placement,
consider the location of combustible materials. If the
proximity of the exhaust system to the combustible
materials cannot be avoided, follow a regular
maintenance schedule to ensure that combustible
materials are kept away from the exhaust pipes after
installation.
Combustible materials include building
materials as well as natural surroundings. Keep dry field
grass, foliage, and combustible landscaping material a
safe distance from the exhaust system.
2.6 Double-Sleeved Thimbles
If the exhaust pipe passes through a wall or roof, use a
double-sleeved exhaust thimble to prevent the
transmission of exhaust pipe heat to the combustible
material. Figure 2-3 shows construction details of a
typical double-sleeved thimble in which exhaust piping
passes through a combustible structure. Sheet metal
shops usually fabricate thimbles using installation
engineer's specifications and drawings.
Construct the thimble so it extends at least 254 mm
(10 in.) both inside and outside the structure's surface.
Openings at both ends of the thimble allow cooling air to
circulate through the thimble. If screening is used on the
outer end to keep birds and animals from entering the
18
Section 2 Exhaust Systems
thimble, use a mesh large enough to allow unrestricted
air circulation through the thimble. See Section 2.7 for
additional exhaust outlet location and protection
considerations.
1
6
7
10
15
14
1. Rain cap (or gradual U bend)
2. Rain shield
3. 254 mm (10 in.) minimum
4. 25 mm (1 in.) minimum
5. Exhaust pipe
6. Ventilation holes at both ends
7. 254 mm (10 in.) minimum
8. 25 mm (1 in.) minimum
9. Flashing
10. Inner sleeve
11. Outer sleeve
12. Thimble outer diameter
13. 254 mm (10 in.) minimum outside
14. 254 mm (10 in.) minimum inside
15. Exhaust pipe diameter
Figure 2-3 Double-Sleeved Thimbles and Rain Cap
2
3
9
4
8
5
6
11
12
13
TP-5700-5
TP-6609 6/08
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