Trane CVHH - Page 36

Vent Piping
36 CVHH-SVX001A-EN
• L = equivalent length of discharge piping, meters
• C
r
= rated capacity as stamped on the relief device in
SCFM (conversion: kg/s = SCFM * 0.0764 / 132.28)
C
r
= C value from
Table 8, p. 35 (convert C in kg/s to lb/
min for IP; lb/min = (kg/s) / 132.28)
• f = Moody friction factor in fully turbulent flow
• d = inside diameter of pipe or tube, mm
• ln = natural logarithm
• P
2
= absolute pressure at outlet of discharge piping,
kPa (atmospheric pressure)
• P
0
= allowed back pressure (absolute) at the outlet of
pressure relief device, kPa
P
0
= (0.15 P) + atmospheric pressure
Figure 23. Rupture disk vent pipe sizing (SI units); for use with
Table 8, p. 35
Note: This figure, provided as a refer ence, is based on ASHRAE St andard 15. Vent line size is typically dict ated by stat e or local code which m ay be different
from ASHRAE Standard 15 requirements.
Pipe Size ( I .D.)
friction factor
150 DN (6 NPS)
154 mm (6.06 in.)
f = 0.0149
100 DN (4 NPS)
102 mm (4.03 in.)
f = 0.0163
80 DN (3 NPS)
78 mm (3.07 in.)
f = 0.0173
125 DN (5 NPS)
128 mm (5.05 in.)
f = 0.0155
Pipe size as a Function of “C” Value and Length of Run
10
1
0
100
100010
L = Pipe Length ( Equivalent Meters)
( Meters x 3 .28 1 = Feet)
“C” Value (kg/s)
ASHRAE Standard 15
L =
7.4381x10
-15
d
5
(P
2
0
- P
2
2
)
-
d * ln(P
0
/ P
2
)
fC
2
R
500f