Cascaded Pumps – How They Can Get You Another Decade of Vacuum

Introduction

Cascaded pumps have a noticeable improvement to how far down they can pull vacuum when compared to a standalone pump. This particular combination of cascading pumps allows us to first pull down the vacuum of the first chamber by decreasing the pressure difference between the first pump’s inlet and exhaust. This reduced the load and thus gave it some more headroom.

The second pump acts as a backing pump, which is similar to a turbo configuration.

The test set up for how the pumps were arranged can be seen in the diagram below.

The set up can be described as such:

• A ~1L chamber was set up with DPCP sensors – one at the end of the chamber and the other at the first pump inlet.
• The exhaust of the first pump was then connected via a hose to another ~1L chamber.
• The second pump was then attached to the second chamber, where another sensor was placed at the second pump inlet.

Results

The results of the testing for the cascaded pumps can be seen in the graphs below.

With just one IDP3 in the system, we can see how it can only pull down to about 0.1 Torr. If we introduce a 15 sccm bleed to the system, it can only maintain above 0.4 Torr.

Incorporating a second IDP3 pump in series yields a much lower pressure, pulling down to about 0.01 Torr. This is 10 times lower. However, introducing the same 15 sccm bleed we still only see above 0.4 Torr.

For comparison, the second (backing) IDP3 pump sees pressure of over 1 Torr without any flow, and 15 Torr with bleed. This shows that the backing pump cannot pull down as much because of the first pump’s constant exhaust of gas into this backing pump.

Similarly, we found the same trend with the IDP10 cascaded pumps experiment.

In this case, we have a larger, more powerful pump so the control measurements show lower pressures of 0.025 Torr without flow and 0.15 Torr with a 15 sccm bleed.

Taking the next step and putting 10 IDP10‘s together yields us 0.01 Torr after 15 minutes without any bleed in the system, much better than what we were getting with one pump. When adding 15 sccm the pressure is just below 0.15 Torr, which is a slight and hard-to-notice improvement when compared to a single pump.

Above are the backing pumps, or second pumps, in the cascaded system. These are for comparison, showing that the backing pump was a significantly higher pressure because of the first IDP10 exhaust feeding into the inlet of a constant flow of gas. After 15 minutes the pressures sat between 40 and 50 Torr.

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