Kohler 15REYG, Installation Manual

Page: 23 / 68

TP-6727 10/11 23 Section 2 Open Units
3. Refer to the generator set specification sheet for:
a. Engine exhaust flow at rated kW in m
3
/min.
(cfm)
Example: 8.35 m
3
/min. (295 cfm)
b. Maximum allowable backpressure in kPa (in. of
Hg)
Example: 10.2 kPa (3.0 in. Hg)
4. Refer to the submittal catalog for:
a. The flexible exhaust adapter part number
Example: 324089
b. Flexible exhaust adapter, flexible section length
Example: 432 mm (17 in.)
5. Count the number of elbows and flexible sections in
the exhaust system between the engine and the
exhaust system outlet. Compare the radius of the
bend (R) to the pipe diameter (D). Diameter is the
nominal pipe diameter in inches. Determine the
equivalent length in m (ft.) of straight pipe for the
elbows and flexible sections from the following:
Bend
Angle
Elbow Type
Bend
Radius Equivalent
Length, ft.
90
°
Close R = D 32 x D* / 12
90
°
Medium R = 2D 10 x D* / 12
90
°
Sweep R = 4D 8 x D* / 12
45
°
Close R = D 15 x D* / 12
45
°
Sweep R = 4D 9 x D* / 12
Flex Sections — 2 x Length
[
/ 12
* Use the diameter of the silencer inlet in inches from
step 4 for the initial calculation. If the results from
step 8 indicate excessive backpressure drop, then
recalculate using the larger-diameter pipe size
selected.
[
Use the flexible exhaust adapter length from step 4
and add any additional flex sections in the exhaust
system expressed in
inches .
Convert the equivalent pipe length calculated in
feet to meters using ft. x 0.305 = m, as needed.
Examples:
For two 45
_
sweep elbows:
9 x 2.0 in. / 12 = 1.5 equiv. ft. or 0.46 equiv. m
Multiply by 2 for 2 elbows:
2 x 1.5 ft. = 3.0 equivalent ft. or
2 x 0.46 m = 0.92 equiv. m
Flexible sections:
2 x 17 in. / 12 = 2.8 equiv. ft. or 0.86 equiv. m
Equivalent of straight pipe:
3.0 + 2.8 = 5.8 equiv. straight ft.
0.9 + 0.86 = 1.76 equiv. straight m
6. Determine the total length of straight pipe used in
the exhaust system. Add this calculation to the
equivalent length for elbows and flexible sections
obtained in step 5.
Example:
Straight pipe = 3.0 m (10 ft.).
Equivalent straight pipe from step 5: 1.76 m (5.8 ft.)
3.0 m + 1.76 m =4 .76 m or
10 ft. + 5.8 ft. = 15.8 ft. total
7. Refer to Figure 2-13. Place a straight edge across
the chart with the edge in line with the pipe size in
inches (D) on the right column from step 4 and the
engine exhaust flow (Q) from step 2 on the left
column.
Read backpressure kPa/m or in. of Hg/ft. (
∆
P) from
the center column. Calculate the total piping
system backpressure by multiplying the total
equivalent straight pipe in m (ft.) from step 6 by the
kPa/m or in. of Hg/ft. of pipe from this step.
Example:
4.76 equiv. m x 0.5 kPa/m =
2.4 total system backpressure in kPa
15.8 equiv. ft. x 0.048 in. Hg/ft. =
0.76 total system backpressure in inches of Hg.
8. Add the backpressure of the piping determined in
step 7 to the backpressure of the silencer and
exhaust pipe determined in steps 1 and 2. The total
should not exceed the engine manufacturer’s
maximum
allowable system backpressure
determined in step 2 or on the generator set’s
specification sheet.
If the total exceeds the
maximum, use a larger pipe size or silencer or both.
Repeat the calculation if new components are
selected to verify that the system backpressure
would not exceed the limit using the larger
component(s).
Example:
2.4+ 1.7 + 5.45 kPa = 9.55 kPa
Maximum allowable backpressure = 10.2 kPa
9.55 <10.2; backpressure drop is acceptable
0.76 +0.5 + 1.6 in. Hg. = 2.86 in. Hg.
Maximum allowable backpressure = 2.88 in. of Hg.
2.86 < 3 in Hg; backpressure drop is acceptable