Equation (1.24) tells us that only in the situation where C = ∞ (meaning
that the flow resistance is equal to 0) will S = Seff. A number of helpful
equations is available to the vacuum technologist for calculating the conductance
value C for piping sections. The conductance values for valves,
cold traps, separators and vapor barriers will, as a rule, have to be
determined empirically.
It should be noted that in general that the conductance in a vacuum component
is not a constant value which is independent of prevailing vacuum
levels, but rather depends strongly on the nature of the flow (continuum or
molecular flow; see below) and thus on pressure. When using conductance
indices in vacuum technology calculations, therefore, it is always necessary
to pay attention to the fact that only the conductance values