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Basic Pump Throughput Concepts

What is Pump Throughput?

The manufacturer of a vacuum pump supplies a chart for each pump showing pumping speed (volume in unit time) vs pressure. The example, for a fictitious pump, shows the pumping speed is substantially constant over a large pressure range.

By multiplying pumping speed by pressure at which that pumping speed occurs, we get a measure called pump throughput. We can tabulate those results, as shown in the table below, or plot them as a graph of pressure vs pump throughput. As is clear from the chart, pump throughput (which might also be called mass flow) decreases proportionally with pressure, at least over the pressure range where pumping speed is constant.

Pumping Speed Pressure Pressure x Pumping Speed
100 L/sec 10 torr 1000 torr.liter/sec
100 L/sec 1 torr 100 torr.liter/sec
100 L/sec 0.1 torr 10 torr.liter/sec
100 L/sec 0.01 torr 1 torr.liter/sec

Expressed simply, throughput is a measure of the quantity of gas the pump can remove from its inlet, at a given pressure, in unit time.

But note, the word “quantity” can be replaced by “amount”, “mass flow”, or “number of atoms/molecules” and still be correct.

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