LACO Technologies TITAN VERSA C - Page 181

10 APPENDIX
LACO Technologies TITAN VERSA Operations and Maintenance Manual 171
10.1.4.2. Leak Rate vs. Pressure
• Viscous Flow: Q
V
= K/n (P
2
- P
2
)
• Molecular Flow: Q
M
= K(T/M)
1/2
(P
1
- P
2
)
Where:
• Q = Leak Rate
• K= Constant relating leak path geometry
• n = Gas Viscosity
• M = Gas Molecular Weight
• T = Absolute Temperature
• P
1,2
= Upstream and Downstream Absolute Pressure
Example: A helium leak in the viscous flow regime with 10 atm upstream (internal) and
1 atm downstream pressure has a leak rate of 0.001 atm-cc/sec. If the upstream
pressure was doubled to 20 atm the new leak rate would be:
Q
V'NEW
= Q
V'OLD
((P
1'NEW
2
– P
2'NEW
2
) / (P
1'OLD
2
– P
2'OLD
2
))
Q
V'NEW
= 0.001 ((20
2
- 1
2
)/(10
2
- 1
2
)) = 0.004 atm-cc/sec
Using the table above, the equivalent leak rate for air under the same conditions is:
Q
V,AIR
= 0.004 (1.08) = 0.0043