FAQ - Step by Step vacuum system construction and testing

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Richard Hull
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FAQ - Step by Step vacuum system construction and testing

Post by Richard Hull » Sat Jan 12, 2019 12:02 am

Mechanical pump testing

A tremendous amount of detailed data has already been written about this already in these FAQs. Refer to them for in-depth details.
The important thing is to put a known good TC gauge on on the end of at least an 8-inch length of well sealed hose when you think it is fully ready for vacuum work. If you can't get a 30 micron vacuum or better in under 3 minutes, you must repair or discard the pump it will not really satisfy full fusion requirements in a completed vacuum system. It would be OK for a limited demo system. For the sake of the rest of this FAQ lets say you read 12 microns.

Before we start. You will be tempted to purchase many surplus items that are very inexpensive. For many here, it will prove absolutely necessary. However, testing will go much faster, step-wise, if you can adapt your gauge at every assembly point or step in assembling your system. If you are well off enough to buy new or are willing to wait for the right piece with the right fittings to come along, this can go much easier and faster. I highly recommend selecting a single type fitting to use throughout the assembly and testing of your vacuum system. The KF fitting is perfectly suitable for all fusor systems. KF-25 size is most normal. Conflat fittings while more likely to be encountered on surplus materials are a good bit more expensive. They are found on all professional vacuum systems. The most common conflat flange is the 2.75-inch style. Be advised that at every junction in your system where there are two different connectors, you will be forced to purchase an adapter to link or join them. All adapters are very expensive!!

The Foreline

It is important to keep this line as short as possible through the largest diameter tubing reasonable. A good total foreline length is under 15-inches.
Always place your first gauge (TC gauge preferably) at the far end of the fore-line away from the mechanical pump, but just before your secondary pump isolation valve which must be in the fore-line.

With this valve closed, pump down the fore-line. It better be the exact bottom pressure you obtained in the pump test. (12 microns) If not, you have a significant and intolerable leak. fix it before moving on. If you can't pump down a fore-line that is sealed off, you are lost.

Secondary pump test

Now that you have installed your turbo pump or diffusion pump and the valve off of it to the chamber, (fusor isolation valve), we need to pump down the entire system to this point with the fusor isolation valve closed tightly, but the fore-line valve wide open. You have added a rather huge volume to your system in the form of a turbo or diff pump. The mechanical pump down will take longer. This is normal and expected. A number of issues can make this a long and tedious project. Moisture in the secondary pump, real leaks, etc. If you can't pump the entire system to this point to 25 microns, you have problems. Solve them. Do not turn on the secondary pump!! ***let us say for the purpose this post you can't get below 18 microns. (This is pretty good)

The Fusor installation and testing

Here is the final hurdle. You must have a low reading vacuum gauge attached to and reading the fusor's chamber pressure! As you also have gas lines, high voltage feed throughs, view ports and other possible leaky venues, it would be great, at this time, to just plug them up with blank offs and, if possible, install them one at a time. If the tight spaces around the fusor prevent this then just hook the finished chamber to the fusor isolation valve.

I suggest that you now pump down the system with the fusor isolation valve still closed. (back to our hypothetical 18 microns). Do not turn on the diff pump or the turbo as above!! Now, open the fusor isolation valve from the secondary pump to the fusor. Wow!!!....The TC gauge falls immediately to virtual atmosphere and stays there. Tick, tock, tick, tock.... Ultimately, hopefully in less than one minute, you see the TC gauge respond dropping to 500 microns and then, slowing significantly at 50 microns. Over about 10 minutes it should be between 40-30 microns or, hopefully, less. If more than 40 microns, you now know for sure you possibly have a real or virtual leak in the many attachments or welds in the fusor itself. Fix them until you are below 50 microns in 10 minutes of pumping. The TC gauge and the fusor gauge should correspond to the same reading within a few microns to as many as ten microns +/- (Suppose we read 25 microns.)

Only now can you start your secondary pump!

Here is where you will see a difference form between your TC gauge reading and the fusor's chamber pressure reading. If you have a turbo pump, you should see a drop in chamber pressure almost immediately and a rise in the TC gauge pressure. This is normal as the Turbo is blasting molecules at the fore-line that the mechanical pump could not work on.

If you are running a diff pump, the TC gauge will show a rise in pressure in the fore-line long before the fusor chamber pressure starts to drop. This is because the oil is getting hot enough to boil off the water molecules trapped in it. This pressure of boiling water is seen in the fore-line and is taken care of by the mechanical pump. Slowly the pressure will drop until the oil starts its jet action and then the pressure will really tank or drop in the fusor chamber very fast and then level off at some sub micron level.

Assuming all the above to be the case with air in the chamber, then you are good for fusion, just add deuterium and a lotta' volts....

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
Retired now...Doing only what I want and not what I should...every day is a saturday.

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