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2.1.5 Pumping speed of pumping stages connected in series

Let us consider a vacuum pump having a pumping speed S0 and a compression ratio K0. The pump has backflow losses through gaps having conductivity LR. Let inlet pressure be p1 and discharge pressure p2. An additional pump having a pumping speed Sv is connected on the outlet side.

The pumping station will displace the following volume of gas:

Formula 2-2:

Pump combination gas flow

Where LR << S0, backflow conductivity LR is:

Formula 2-3:

Backflow conductivity

and the real compression ratio is:

Formula 2-4:

Real compression ratio

Using the above formulas, it therefore follows that the pumping speed S of a two-stage pumping station will be:

Formula 2-5:

Recursion pumping speed

This formula can also be used as the recursion formula for multiple pumping stages that are connected in series by starting with the pumping speed Sv of the last stage and inserting the K0 and S0 of the preceding stage.

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