How Do You Connect Multiple Diffusion Pumps for UHV Systems?

[SupaVillain]

If using diffusion pumps (2 or 3 in series) to achieve ultra high vacuum, how do you hook them up together, for example adding them onto a system like in the provided picture? Would you use T-connectors to put them all on the same input and output valves or would you have valves for each pump?

 

[Quantum Defect]

If using diffusion pumps (2 or 3 in series) to achieve ultra high vacuum, how do you hook them up together, for example adding them onto a system like in the provided picture? Would you use T-connectors to put them all on the same input and output valves or would you have valves for each pump?

I have never seen Diffusion pumps used in series. Generally, the input end of a Diff. pump is at high vacuum, while the foreline pressure is only low vacuum. The foreline is typically pumped by a mechanical pump, as shown in your diagram.

For UHV work, you might see Diff pumps being used to get to high vacuum, followed by other kinds of pumps to get to even higher vacuum (ion pumps, etc.)

Generally, folks will use a large-aperture gate valve over a diffusion pump (to keep from throttling the pump). If you are concerned about backstreaming of oil into the vacuum system, you can add some kind of a cold trap between the pump and the gate valve.

O'Hanlon's, "A Users Guide to Vacuum Technology" is a good book to look for.

 

[SupaVillain]

Well after doing some research I mean even wikipedia says diffusion pumps can get to UHV and that picture shows a system that can supposedly get to 10-7 torr. They have been engineered in series or parallel because vacuum can work in accumulation. I guess I am just going to to have to do research on the vacuum strength of the valves and lines themselves.

 

[M Quack]

Your diagram looks OK to me. You should make sure that the connection from the chamber to the diffusion pump is as short, straight, and large diameter as possible to maximize pumping efficiency. One way to do this is to use a large gate valve for the High-vac valve.

If you want to use several diffusion pumps, then you should connect them in parallel, not in series. For each you should try for a short, wide, straight connection to the vessel to be pumped. This is not always possible.

Finally, diffusion pumps are not the most convenient technology to use. If you are thinking about building a system from scratch, you should consider using a turbomolecular (turbo) pump and an oil-free roughing pump instead. These are robust, efficient and easy to use, furthermore they minimize the risk of contaminating your chamber if hydrocarbonds and turning it into a deep-fryer. (Consider what happens in case of a power failure. Will the vacuum suck the oil out of the diffusion pump and into the chamber?)

 

[f95toli]

Well after doing some research I mean even wikipedia says diffusion pumps can get to UHV and that picture shows a system that can supposedly get to 10-7 torr.

10e-7 is not really UHV, You should be able to reach that with a good turbopump/roughing pump combination provided you can bake out your system. If you want a better vacuum you should consider adding an ion pump.

Diffusion pumps are not nearly as popular as they used to be for reasons already mentioned above, they have (mostly) been replaced by modern turbo pumps.