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Re: I think I have a fusor chamber.

Posted: Sun Nov 12, 2017 5:08 pm
by Dennis P Brown
Controlling the current to the diffusion pump heater sounds like a waste of time and effort. Controlling the vacuum rate via a gate valve is extremely fast; controlling current to a heater takes a long time (even for major current changes.)

My main gate valve is a manual butterfly type and works extremely well.

Re: I think I have a fusor chamber.

Posted: Sun Nov 12, 2017 7:10 pm
by Silviu Tamasdan
Eh, it's not complicated to do (I have a PWM already built with the appropriate rating) and at worst it won't be useful. I was thinking that it may be handy for long runs at reduced pumping speed (not to make sudden changes during a run). Especially since it looks like I'm leaning more towards using a pump that is oversized for my chamber's needs.

Re: I think I have a fusor chamber.

Posted: Mon Nov 13, 2017 7:13 am
by Richard Hull
Throttling the boiler electrically sounds bizarre. I would think the oil is either hot enough to form the needed jetting in the stack or it is not. This is what I observe at pretty much a single temperature level in my diff pump. It starts working at a specific temperature, dropping the fusor's pressure to a given sub micron level and a temperature climb of another 40 deg C does not deepen the vacuum one iota. It is kind of an on-off senario. One moment It's not pumping at all then, suddenly, it is going gang busters. Diff pumps do not seem to incrementally pump with increasing temperatures.

Once you actually run a diff pump with a pressure gauge capable of seeing it start to pump, you will observe this. Once it starts to work that is as low as it will go. There is no middle ground of variable pumping speed. The throttle valve on top of the diff pump to the fusor controls and can vary the pumping speed.

Richard Hull

Re: I think I have a fusor chamber.

Posted: Mon Nov 13, 2017 9:05 am
by John Futter
Diff pumps are a semi closed loop feedback system
DC 704 will run at one temp with a standard heater DC705 at another temp albeit higher
If you use Santovac it will be an even higher temp.
The diff pump is a self regulating system using the cooling in the upper parts and the super heated fluid in the lower parts ( giving the vapour flow) to establish the correct operating conditions all of this due to pump design and operating oil characteristics.
do not try to circumvent this setup it will lead to tears!!!
a burping unstable pump is not another variable you need to introduce to a fusor setup.
side effects will include contaminated vacuum gauges and chambers from this burping (farting) phenomeom and silicon oil coated surfaces are a B#$%^tch to clean properly.
Been there
Done that
Got the Tee shirt

Re: I think I have a fusor chamber.

Posted: Mon Nov 13, 2017 11:22 am
by Silviu Tamasdan
OK scratch that part of the plan. Everything else stays the same though. The HV feedthrough definitely needs to go into one pf the KF50 because that is the only way to adapt mine.

Re: I think I have a fusor chamber.

Posted: Thu Dec 21, 2017 6:40 pm
by Silviu Tamasdan
Quick update, KF40 manual angle bellows valve. I got it for a good price (the cheapest similar KF16 valve was about double the cost).