Vacuum Systems with Series Connected Pumps - Get Answers Now

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    Pumps Series Vacuum
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Discussion Overview

The discussion revolves around the operation and understanding of vacuum systems, specifically focusing on the configuration of two side channel blowers connected in series. Participants explore the implications of this setup on pressure differentials and vacuum generation, with references to practical applications and theoretical models.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant seeks clarification on how two blowers connected in series can achieve a combined vacuum of -15kPa, given that each produces -8kPa on the inlet.
  • Another participant compares the operation of the two pumps to batteries in series, suggesting that the pressure drop could be additive, potentially reaching around 16kPa.
  • A different viewpoint discusses the common practice of using integral 2-stage pump systems to enhance compression ratios, suggesting that staging can lower ultimate pressure to a specified design point.
  • One participant shares their experience with mass spectrometer design, noting that they typically use a roughing pump and multiple turbo pumps, which do not operate in series in the same way as the blowers discussed.
  • A participant questions the initial claim about outlet and inlet pressures being "roughly" the same, emphasizing the need for a pressure differential for airflow.
  • Another participant mentions that turbo pumps can be used in series with a rough pump, indicating a different configuration than the one being discussed.
  • One participant expresses uncertainty about the design of the pumps they have observed, acknowledging that they have not seen two identical pumps in series.
  • A participant reflects on their findings regarding the performance of a single blower at 4500 rpm, suggesting that two blowers could theoretically generate a -40kPa vacuum, raising questions about the implications for outlet pressure.

Areas of Agreement / Disagreement

Participants express a range of views on the operation of vacuum systems, with no consensus reached on the effectiveness or configuration of the pumps in series. Some agree on the theoretical aspects of pressure addition, while others challenge the practicality of such configurations.

Contextual Notes

Participants highlight various assumptions about pressure differentials, operational configurations, and the specific applications of different types of pumps, which remain unresolved within the discussion.

Who May Find This Useful

Individuals interested in vacuum system design, engineering applications of pumps, and those studying the principles of pressure differentials in fluid dynamics may find this discussion relevant.

Kamilan
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Hello,

I was hoping for some information on vacuum systems.

There are two side channel blowers that produce -8kPa of pressure on the inlet. The outlet pressure in roughly the same.

The two blowers are connected in series.

Can some please refer me to some reading material so that I may better understand the system.

When both blowers are running, there is an "combined" vacuum of -15kPa. I don't understand how this is possible?

Can someone shed some like on the matter.

Cheers.
 
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The two vacuum pumps are working like two batteries in series. The pressure drop is similar to the potential difference across a battery. Therefore, if each pump produces a pressure difference of 8 kPa, two in series should reach 16 kPa, a figure close to the number you're mentioning.
 
It is common practice for vacuum pump engineers to apply and even manufacture integral 2-stage pump systems to overcome the compression ratio limitation of a single stage pump. For
example, say your pressure design point is 25"HgA and your available pump can only produce 27.5"HgA then one solution may be to "stage" the existing pump with another. This method enhances the compression limitation of the single pump. By splitting the compression work between two pumps or "stages" we can decrease the ultimate pressure to the specified design point. In your example using two blowers of equal size we can say the staging ratio is 1:1 and the final compression ratio desired is 1.2cr (roughly 30"HgA/25"HgA) or the first pumps inlet is expected to operate at 25"HgA and the 2nd pump discharge is atmosphere or roughly 30"HgA.

Expected interstage and final discharge temperatures must be determined before the final selection.
 
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I am no expert in vacuum. I did work 10 years in a company designing all the electronics for various mass spectrometer. We work with vacuum and 10EE-9 level. We always use one ruffing pump for the system and quite a few turbo pumps for different part of the instrument. I don't believe they are in series because the ruffing pump sits at the bottom of the instrument and the opening connect directly to the vacuum chamber where the little turbo pumps spread out in different part of the instrument. Those turbo pumps don't even start until the pressure was quite low because the those turbo pumps will be destroy if you run it at not low enough pressure. I never saw two identical pump in series because I don't think you can have one single pump go all the way from normal pressure to 10EE-9.
 
Kamilan said:
Hello,

8kPa of pressure on the inlet. The outlet pressure in roughly the same.

The two blowers are connected in series.


When both blowers are running, there is an "combined" vacuum of -15kPa. I don't understand how this is possible?

Are you sure that the outlet and inlet pressures are "roughly" the same?

If there is no pressure differential across the pump then there can be no air flow. That is no driving force
 
turbo pumps are in series with the rough pump. The latter gets down to 0.01 Torr (approx) and from there the turbo kicks in reaches the high vacuum zone
 
Gordianus said:
turbo pumps are in series with the rough pump. The latter gets down to 0.01 Torr (approx) and from there the turbo kicks in reaches the high vacuum zone

It could be true, I did not design the pump controller, just been seeing them on the instrument for years and asked a few questions before. I just never seen two identical vacuum pumps in series. I better get out of this subject!
 
Hello,

Thanks for the reading material. The oulet is fed back into a tank that cannot be pressurised. I'm guessing the outlet pressure must be lower than the inlet vacuum.

The battery in series analogy works for me. I did some further investigations, and the second pumps acts like a cavity forthe first blower.

Think I'm getting there.

Cheers!
 
Hello,

I have just found out that on average when a single blower is run at 4500 rpm we have a -15 to -20 kPa vacuum pressure on the inlet and roughly 30kPa out the outlet.

So we if ran two blowers on series at 4500 rpm then a theoritcal -40 kPa could be generated.

what does that mean for outlet pressure?

Cheers
 

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