Motorising a sapphire leak valve. A failure and success

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Emma Black
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Motorising a sapphire leak valve. A failure and success

Post by Emma Black »

Bit of a tale of frustration to share. For a while now I have been using a sapphire leak valve for the fusors deuterium gas control. As reported by several others, these things are great for the purpose, offering a very good degree of control. They look like this:
VariableLeek.jpg
This particular valve is completely manual and therefore needed to be at arms reach in order to adjust the D2 while the fusor is running. This was fine at first but once the voltages and by extension the xray emissions of the fusor started to increase, it necessitated moving the controls and the valve further away. This lead to a long copper 1/4" pipe being used, which was a bit of a pain. The pipe was difficult to pump down and due to the haphazard way it was routed, lead to the fittings leaking every time the fusor housing cabinet was moved.

The fix: motorised control. Now I also could have just switched to a MFC and still might, but this little project was done using the we had on hand.

Attempt one.
A control box, uninstalled for troubleshooting
IMG_3354.jpg
During testing.
IMG_2908.jpg
This was arduino based and used a stepper motor, connected to the valve via a geared belt. In terms of operation, the side lever on the control box turns the valve up and down. There are two speed settings via a switch and a rotary encoder, which allows you to set the valve to a set position.

In theory this would have worked very nicely. In practice, it was plagued with issues. Before the belt was added any slight misalignment would lead to the motor skipping steps.
Secondly and more importantly there seemed to be a fault with the motor controller itself, occasionally and at random to motor would start rotating all by itself. This only developed while in use, which ruined a couple of fusor runs. I initially thought this was either some kind of buffer overflow in my code like an integer rolling over or a loose connection. Hours of troubleshooting did not not get to the bottom of the issue. Only by swapping the controller, by borrowing the one from another project, was the problem fixed. At this point though I'd already taken it out of operation and reverted to manually operating the valve, my distrust of the little system high.

Attempt two
Now a couple of months on, I had the time to pick this up again and settled on a greatly simplified solution, using a 6rpm 12v motor and a few buttons.

A 3D printed mount and little machined adaptor later and now we have a nice simple motor driven valve. On the control panel there are some forward and backward buttons, half run at 12v and the other two at 3V for some fine control. This was way easier compared to the amount of time spent troubleshooting the previous installation and so far I could not be more pleased with its operation, there is now little to go wrong.

Having the previous digital display to show the position of the valve was nice, but really it good enough to mount the valve so that it was visible and simply count a couple of turns while holding on the button.
IMG_3340.jpg
A little custom mount printed with ABS.
IMG_3342.jpg
Avert you eyes from the mess of epoxy! On this list is to made a VCR to hydrofil canister adaptor.
IMG_3350.jpg
Last edited by Emma Black on Tue Feb 21, 2023 3:01 pm, edited 1 time in total.
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Richard Hull
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Re: Motorising a sapphire leak valve. A failure and success

Post by Richard Hull »

Very inventive solution for remote gas control using the sapphire leak. Great work. Invention and adaptation has no limit for those that can do.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
JoeBallantyne
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Re: Motorising a sapphire leak valve. A failure and success

Post by JoeBallantyne »

Great solution! I like how it is simple, straightforward, and pretty much immune to noise. Sometimes not using a computer/microcontroller as part of a solution is better - especially in an electrically noisy, radiation exposed environment like a fusor.

I noticed that the images you have in your post are not actually uploaded to fusor.net.

I would encourage you to upload all the images you put in posts up to fusor.net, so we aren't dependent on 3rd party websites staying up for them to not be lost. (Granted, fusor.net has had its own issues with lost images, but links to external sites are pretty much guaranteed to go down eventually.)

I have found that if you figure out in advance which shots you will post, and you upload and insert them inline in reverse order (last image in post is first one uploaded, first image in post is last one uploaded) that it works OK. You also have to make sure to click on the line where you want to insert the image, AFTER uploading it and BEFORE you click on insert image. You also need at least 2 lines of whitespace before and after every inserted image in order to make it look right.

Joe.
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Emma Black
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Re: Motorising a sapphire leak valve. A failure and success

Post by Emma Black »

Yeah I was getting some issues previously with the electrical noise. Arduinos seem especially vulnerable.

Good point about the images, there is few things more frustrating than a thread with missing images - I have re-uploaded.
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