Vacuum Systems with Series Connected Pumps - Get Answers Now

[Kamilan]

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.

 

[Gordianus]

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.

 

[desistorm]

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.

 

[yungman]

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.

 

[Driftwood1]

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

 

[Gordianus]

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

 

[yungman]

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!

 

[Kamilan]

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!

 

[Kamilan]

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