Vacuum Chamber Construction

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Richard Hull
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Re: Vacuum Chamber Construction

Post by Richard Hull » Fri Mar 06, 2020 4:42 am

It is obvious that the pump was in a place or position where the pump would not allow for easy draining to replace oil. The tube will go to a drain pan at a lower, convenient location. The hose would have a petcock that could be opened to drain the fouled or old oil.

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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Nicolas Krause
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Re: Vacuum Chamber Construction

Post by Nicolas Krause » Fri Mar 06, 2020 5:47 pm

Thanks for the explanation Richard, I do have another question. I'm missing a small number of vacuum parts for the hookup to my chamber, a couple clamps etc. that I plan on ordering soon. Once those parts arrive, if I put my turbopump in series with my backing pump, and leave the turbopump off, can I just turn on the backing pump without causing any problems? Having read a number of other threads I know that if I turn on the turbopump without the backing pump operating I can do some serious damage, but if the turbopump is off will it just act as a bit of additional tubing?

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Richard Hull
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Re: Vacuum Chamber Construction

Post by Richard Hull » Fri Mar 06, 2020 7:59 pm

Absolutely! Same goes for a diff pump. It is just another "hanger-on" in any vacuum system if it is not turned on. The proper way to work a system is to open all valves and pump the entire vacuum system down as low as the mechanical pump can go. (hopefully at or below 50 microns) Once at fore-line vacuum, the secondary pump (turbo or diff pump), is turned on and you are off to the races from there.

All of the above assumes that your system is sealed and tested. During testing, a stepped assembly process is demanded to be sure you are sealed at each step. This can be a tedious process. Newbies tend to assemble the entire system and then wonder why they can't get a good vacuum as they now have to hunt for issues and leaks.

System assembly absolutely demands a TC gauge at minimum!!! In the last stage a deeper reading gauge on the reactor vessel would be nice, leaving the TC gauge in the fore-line permanently. This means you need a lot of blank offs, clamps and adapters if seeking to do a professional level job of it.

Note: Valves in a vacuum system are more for isolation, shut-down and compartmentalized tear down or modification of the system without fouling the entire business if one component needs replacement or a new one added in the middle of the system. There is no such thing as too many valves.....(if you can afford good ones.)

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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Nicolas Krause
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Re: Vacuum Chamber Construction

Post by Nicolas Krause » Sat Mar 07, 2020 6:47 pm

Earlier this week, my 8020 frame arrived. I had to wait a few days for my M8 Tap to arrive, but on Friday it did and I've completed tapping the ends of the extrusion so it can all be put together. I plan on mounting the vacuum chamber in the center of the frame.
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Re: Vacuum Chamber Construction

Post by John Futter » Sat Mar 07, 2020 10:03 pm

Nicolas
I would srongly suggest you do a pressure test on your chamber first.
Ie blank off everthing and feed shop air at 15psi (no more)into your chamber through your gas feed line
Use 50:50 detergent and water and go round every weld and vacuum joint with a small paint brush dipped in the detergent water mix and look for foaming or bubble formation
this method far quicker than trying to use vacuum in the first instance
only when you pass this stage put the chamber under vacuum

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Richard Hull
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Re: Vacuum Chamber Construction

Post by Richard Hull » Sun Mar 08, 2020 12:55 am

As the whole device is SS, I would pressurize it to 30 psi and put it in a 5 gallon bucket of water. Have a grease pencil handy.

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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Nicolas Krause
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Re: Vacuum Chamber Construction

Post by Nicolas Krause » Sun Mar 08, 2020 5:53 am

Thanks for the suggestion John, I'll definitely look at doing that. Currently in an apartment in the great white north, so I'll have to poke around and see if I can find a compressor of some sorts.

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Rich Feldman
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Re: Vacuum Chamber Construction

Post by Rich Feldman » Sun Mar 08, 2020 6:02 am

Add a Schrader or Presta valve stem adapter to one port, e,g. gas inlet hose.
Then use a bicycle tire pump, or haul the chamber over to some gas station or fabrication shop.
All models are wrong; some models are useful. -- George Box

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Re: Vacuum Chamber Construction

Post by Nicolas Krause » Wed Mar 18, 2020 1:26 am

I'm currently trying to tap a blank for my vacuum chamber, to use as a port for my thermocouple gauge and also for the pressure test. Based on Rich's suggestion I found a 1/8 NPT to schraeder valve fitting that will allow me to hook up my bicycle pump and look for leaks. I used my Machinery's Handbook and grabbed a 5/16 drill bit for the initial hole which went fine. However trying to tap the hole was a no go. My tap would not bite, and looking at the tap itself it says a "Q" drill bit must be used to drill the initial hole. I assume I was unable to start the tap because the hole I drilled was too small, but I believe I've correctly confirmed for my thermocouple gauge that is a 1/8 NPT male fitting. Have I made a mistake somewhere? Did I select an incorrect tap?

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Rich Feldman
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Re: Vacuum Chamber Construction

Post by Rich Feldman » Wed Mar 18, 2020 1:50 am

I've tapped plenty of 1/8 NPT (27 tpi) threaded holes, but don't remember the starting size. 5/16 seems kind of small. Isn't the OD of the pipe, at big end of taper, 0.405"? Consider a tapered reamer with T-handle to adjust your starter hole. Could always practice in a scrap of aluminum or brass.

Schrader valves are held shut by a spring, of course, and open when filling attachment depresses the pin. I think the spring is plenty strong to resist suction when vacuum is inside. But consider the reason metal valve caps with o-ring seals have been available since 19th century.
All models are wrong; some models are useful. -- George Box

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