Regardless of some losses from flanches or tubes, and the the turbo pumps have mostly identical specifications. Which method will give me the higher throughput and the better end vacuum?
Two turbos pumping down simultaneously the same chamber backed by one mechanical pump is the correct option. Never one after another. The second would be pumping the small output volume of the first one and that would be a waste. Now I am aware of the two-stage pumps which are basically one after another, but first that is a different pump that you would have to buy and that it is not what you want, and second that turbo is designed to be used when you have two consecutive quasi-isolated areas at different pressures (differential pumping).
Ok, sounds understandable. Will it make a difference to only use one turbo pump? Both have an end pressure of 1e-8 mBar.
The answer depends on a number of factors:
What sort of pressure are you planning to obtain?
Which is the material of the wall of your chamber?
Can you "bake" your chamber to eliminate absorbed in the walls gases, such as water vapor?
Depending in what sort of vacuum you want you would have to take into account degassing from the walls for instance, if we are talking in achieving 10^-9 torr.
In what time you want to achieve the level of vacuum?
In general 2 is better than one.
The use of 2 turbo pumps will help mostly in decreasing the time to reach the ultimate pressure (when opening and closing the vacuum chamber is often) but the ultimate pressure will not be significantly better.
Maciej, usually the turbo pump has an inlet of 6-10 " (meaning a large opening) which gives you good pumping speed and flow. If you serialize them, then the 2.75 " output port of one turbo (about 3-4 cm) will be "choking" that large inlet (12-25 cm) and your conductance will be terrible.
Mi, you are correct if you refer to old Pfeiffer pumps of 20 yrs ago, which used wicks and oil for bearings lubrication. Modern pumps have magnetic bearings these days, and if they use oil at all it is not exposed to the vacuum.
I fully agree with Maciej Jankowski answer. If your vacuum system is properly prepared (stainless steel, baked-out etc.) and you have no other sources of gas, than 99% of your residual atmosphere in UHV should be hydrogen. This hydrogen outgassing from stainless steel walls will define the ultimate pressure. On the other hand turbo has very bad compression ratio for hydrogen compared to other gases, hence it makes sense two use two turbo in serial. Best is to use oil-free turbo pump as the first one.
I agree with Maciej's statement. Two TMPs with series connection can increase the compression ratio to improve the base pressure of the vacuum system.
Hello Matthias,
Of course you can play with the two turbomolecular pump to improve the situation a bit. However, turbopump are instrinsically less suitable for pumping hydrogen as compared to nitrogen or other active gases. As hydrogen is the main partial specie in UHV-XHV system and NEG (Non Evaporable Getter) pumps are well known to pump hydrogen very effectively, a different approach could be to simply add a NEG pump to the turbo pump, rather than combining two turbo together. You can have pumping speed in excess of 2000 l/s (H2) in a NEG pump on a CF DN 100 flange. For pumping hydrogen NEG pumps are quite the choice. Many Accelerator facilities use them to boost the vacuum. Just a different perspective. Take care
Paolo
Have no sense to put it in series! They do not suck the air, but any molecule which enter and get hit by a blade (with a particular angle) will be send it to the exit. So you should connect it in parallel to increase the area.
connecting them in series will result in a better vaccum and connecting in parallel will result in higher flowrate. check these links for further understanding.
http://www.engineeringtoolbox.com/pumps-parallel-serial-d_636.html
I am persuaded by Maciej Jankowski's statement on Apr 27, 2014 about two turbos in series. But for two turbos in parallel, he said "I would strongly advice you to not connect simultaneously two turbo pumps to one chamber". Is there any risk to connect two turbos to one chamber in parallel? I thought this combination could increase the flow rate if time efficiency (instead of the base pressure) is my only concern?
You could consider putting a molecular drag pump betwen the turbo pump and the roughing pump. However, most turbo pumps these days include a molecular drag pump as the last stage, so I don't know if adding an additional molecular drag pump to back the turbo pump would provide a benefit, but it's worth looking into. As noted in other posts, putting two turbo pumps in parallel might provide higher throughput, but series connection might provide better ultimate vacuum. As far as putting them in parallel is concerned, it is probably a better idea to just get a bigger turbo pump, i.e. one with a bigger throat diameter.
- Badges
- Science topic
- Similar topics
- Phytochemistry
- Extracts