Vacuum Technology and Vacuum Design Handbook for Accelerator ...

Where:
qpV = Throughput flow rate
p = Pressure (Pa)
q pV
= C
- 50 -
( p − p 1 2
At the molecular level, the conductivity of a system is reduced due to the friction of both the walls
of the system and other molecules. As discussed above in “Types of Flow”, these two affects occur
at different flow phases. The total effect of conductance is the sum of the various conductance
elements. In the case where a valve, a trap and an elbow in series each having a different
conductance, the sum is:
1
C
total
1
=
C
valve
1
+
C
trap
)
1
+
C
If the components with different conductances are connected in the flow path in parallel, for
example, 2 different diameter tubes connecting a chamber to a pump then the equation will be:
C = C + C
Total
tube1
tube 2
For the design of vacuum systems used on the accelerators conductance is mostly calculated for
systems in molecular flow.
elbow
Fig 6. Diagram for estimating pipe conductance
Pupp/Hartmann, Vakuumtechnik, Grundlagen und Anwendugen, Hanser Verlag