Fusor Forums

Probably this question has been discussed somewhere, but I'm reading the forum for last 40 mins and still can't find the answer...

I started with the Ideal diagram of foreline pump system for a fusor or demo - everything is more than clear, logical and very easy to understand.

Then I looked at the Vacuum line diagram v2.2 and got quite confused - I don't understand why are there two valves working in parallel ???


I'm talking about the ball valve 1 and the bellows sealed valve 2 - they are both marked as required ones (black edge), so if optional oil trap (3) and valve (4) are not being used, we have valves 1 and 2 connected in parallel ! It has no sense for me, but I have basically zero experience with vacuum systems, so maybe I'm missing something very obvious...

Of course, the easiest explanation could be that the valve two should be an optional one (have a red edge) as well, especially because THE BASIC FUSOR FAQ says that those both valves are optional, but I want to be sure...

Another connected question - let's say we use an oil trap. In this case why the valve 1 is different type than valves 2 and 4, even if they work in the same environment ?

Will be grateful if someone can explain these basic things to me, thanks in advance !

I'd be careful to take some of the diagrams and setups on the forums too seriously. Sure, there's lots of good stuff, but this diagram, for example, has more good looks than merit.

The foreline configuration you want will depend on the level of cleanliness you want. I'll assume that you want it good enough to do basic fusion, but nothing fancy. In that case, get rid of valves 2, 4, the oil trap, as well as the cold trap (unless you use a diff pump). That leaves you with one valve between the rough pump and hi vac pump, another between the hi vac and chamber, and two vent valves. In the foreline, the type of valve is not critical. A ball valve, butterfly valve, or bellows-sealed angle valve are all fine. For the high vac valve, the ideal is a gate valve, followed by a bellows or butterfly. Conductance is somewhat important for the foreline valve, while both conductance and throttle-ability are important for the high vac valve. The foreline vent can be of the cheap type found on Ebay searching "vacuum vent valve". The high vac leak can be a Swagelok diaphragm valve or similar, and just be part of the deuterium line.

Liam review is correct. I will only say that in direct answer to your question for why that is so complex a diagram is that this is for a system that allows the roughing pump to evacuate the chamber without causing the high vac pump to ever see atmosphere (i.e. when one has to rough through the high vac system to pump out the fusor chamber.)

As for the best high vac valve, we all have our own preferences. I feel that for a fusor, the best is a manual butterfly valve (best and easiest manual control for deuterium removal.) Next, a bellows valve (again, manually controlled.) Finally, a gate valve (also, manually controlled) is, for me, last. I currently use a gate valve on my fusor but far preferred my old butterfly valve; however, that system has been retired.

Actually, I would have no problem in understanding everything (in fact I think that even the full diagram is pretty simple even for me) if the valve 2 is shown as an optional one, but it’s shown as a required one. So main mystery (and my direct question) is still here - is the valve 2 shown as a required one just by mistake, or there is something more complex behind it ?

Probably a mistake, I would mostly ignore this diagram. The reason I put gate valves over butterfly valves is that the latter type often leaks through the stem, especially when turned.

Another (not related to the previous one) question - is this needle valve suitable for a fusor De supply system assuming I provide about 0.5 Bar De pressure to it ?
The specs say “Provides fine control down to 10-5 torr” so in my opinion it should be more than adequate for a fusor application, but still would like to check…

I would ditch the entire loop with items 2,3, and 4. In general, for fusor purposes, a trap is not really needed, Same for the cold trap provided you use a turbo. I ran for 18 years doing fusion with no traps of any kind and did fusion just fine over that period and I used a diff pump for 1 of those years.

Richard Hull

Wow, that needle valve looks expensive and will certainly work; there are cheaper ones (I think) that would work as well.

Dennis P Brown wrote: ↑Sun May 15, 2022 7:10 pm there are cheaper ones

It's the cheapest one of this type I could find brand new. There are some used ones for sale, but I don't have enough experience yet to deal with it if the valve doesn't work properly...

P.S. Big thanks to everyone who replied to my questions !

Amazon has a really good vacuum needle valve for under $150; and comes in KF-50 down to KF-10 (all sizes between) and those smaller sizes are cheaper still. This is far cheaper than your unit and will work fine for a fusor.

Search Amazon using:

SHERICH Vacuum Micro Inner Wire Adjustment Needle Valve with Scale, 304 Inner Thread Fine Adjustment Valve WL13H-320P (KF-50)

To be honest I was looking at “real” vacuum equipment shops, forgot that you can buy anything on Amazon these days… But I have some doubts about a quality of this valve - can’t even find any formal specs… Anyway it should be more than enough for my purpose, thank you !

By the way, while looking for the tech info for this valve, I discovered another shop with some (relatively) inexpensive equipment, don’t remember mentioning it here before.

The valve I posted is for letting deuterium into the system. A fusor isn't exactly very sensitive to its operating parameters compared to many experiments nor does one need to control the gas flow too precisely. One can compensate using the high vac pump throttle valve, for instance.

I understand the purpose of this valve, but if it’s too coarse the De control would be too difficult or even impossible (if small movement of the valve’s knob opens the valve too much).
Again, seems it should be absolutely fine for a fusor gas supply system…

A bit confused; are you saying you thought I was suggesting to use this valve to control a tank of deuterium? Of course it can't. One uses a gas tank regulator built for that purpose. The valve I thought you were asking about was to be used for deuterium flow control into the fusor after the tank regulator lowers the tank pressure down to 10 PSI or so. Yes, very different valve systems, of course.

Once again, I throw this image up related to gas system delivery to the fusor.

This is the system I have used for 17 years. Works great. The needle valve has been replaced 2years ago with a $1000 sapphire precision leak. I bought the used precision leak at HEAS flea market for $25.

The second photo is of the leak ready to go into my gas system for fusor V.

Pictures are worth a thousand words and can make things plain that can remain a verbal mystery to the uninformed. Click image to enlarge.

Richard Hull

Dennis P Brown wrote: ↑Tue May 17, 2022 10:35 am A bit confused; are you saying you thought I was suggesting to use this valve to control a tank of deuterium?

Not at all - probably the confusion here because English is clearly not my first language. Of course I’m talking about the De flow control, the tank regulator/valve is completely different story.

Richard Hull wrote: ↑Tue May 17, 2022 12:04 pm Once again, I throw this image up related to gas system delivery to the fusor.

I studied these pictures quite carefully before and have no issues understanding a gas delivery system for a fusor. My question was just if that specific valve is good enough for a flow control.

Thanks everyone !