Fusor Forums

I have an alcatel vacuum pump with a nw 16 inlet port and a pumping speed of 1.5CFM @ 8 microns. I want to hook it up to my diff pump which has an nw 20 inlet port. I tried looking on ebay for some kf 25 hose extensions but they cost alot and have alot of un needed space. But, i found this kf 16- 1/4" vcr firring. Could i use this a vacuum hose to my diff pump with the right adapters? How could this effect my ultimate vacuum?

My recommendation would be to buy yourself some hose adapters for either end, and use a length of heavy natural rubber hose to go in between, but not longer than necessary.

I keep hearing that rubber hoses are very prone to leaking and that kf bellows hoses seal just fine.

Vacuum grade rubber pumping line does not really leak when used in the micron range and works well. That all said, buying new KF stuff is expensive and I generally never do (only exception was a six way KF-25 cluster adapter but that was still rather cheap at the time) - I looked for deals all the time (and get them) by searching the companies that specialize in buying surplus stuff.

Best to get the correct adapter/connector to prevent leaking between equipment/hoses; besides, it makes life easier for connecting the system pieces together.

AS for the fore pump line, if the fitting is KF-20 on the turbo, you need to keep the line as short as possible or pumping efficiency will suffer a lot, otherwise. I have a KF-25 line and it uses a KF-25 to KF-16 adapter to my turbo. That way, my pumping speed isn't as impacted by my line length. Again, got my three point five foot SS bellows line for $25 with shipping; and both end adapter and the clamps for much less. Deals are there! Heck, I got a very high capacity, two stage vacuum pump at the same time for $10 (shipping was a deal at under $25) - this is a spare but I couldn't pass up the deal. These deals are there but you have to search and watch for them.

I dont need three-five feet of bellow line, I only need about 20"

20" is still a rather long foreline, but if you have built yourself into this long a corner, so be it. Running conductance equations vs. pumping speed would frighten the heck out of you. 8 to 12-inches would give you the more normal foreline length. Still, folks with 3 feet of foreline are able to pump a fusor due to its, often, small size and lack of needed pumping speed. Vacuum systems for a fusor only need to be good enough and need not be up to American Vacuum Society standards.

I personally prefer the heavy, thick, yet highly flexible, red rubber, vacuum rated hose as this absorbs a lot of vibration between the two pumps. I use clamped, KF25 hose barbs on each end. I can have my mechanical pump hit and hold 10 microns on the foreline with the foreline to diff pump and diff pump to fusor valves wide open.

In designing any vacuum system with a secondary pump, the general rule is to jam the mechanical pump up as close as you can to the secondary pump to keep the foreline extremely short.

Richard Hull

I am still confused. My pump is elevated to frevent the heater from burning my table bottom. Is 20" of bellows hose too long?

I run a metre of KF16 bellows from my 60l/s turbo, and it pumps just fine. We're not after super dooper scientific vacuums. You are more likely to find the chamber itself and plasma operations in the chamber are the limiting factors to the base pressure rather than the pressures in the foreline hose.

No, 20" is fine, you won't have any issues, heck, my electron microscope has about 8 feet of line between the column and the roughing pump and I have no problems pumping down. And this is very common for EM's, about 8' of hose with a giant pass through weight to absorb vibration. And this is backing a 400l/s diffusion pump.

Now, using a 1/4" line will have issue. Either get the vinyl hose with a spring or red gum rubber hose and you will be fine. Or very thick was vinyl hose works, I am talking about 1/2" wall. Use the same ID hose as the diameter of the fore line on the diff pump.