#2 FAQ - Mechanical Pump - Diffusion pump?

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Tom McCarthy
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Re: FAQ - Mechanical Pump - Diffusion pump?

Post by Tom McCarthy » Fri Jun 14, 2013 7:03 pm

Thanks very much Richard! Wasn't aware that some of these pieces were even needed!

Tom

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Richard Hull
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Re: FAQ - Mechanical Pump - Diffusion pump?

Post by Richard Hull » Fri Jun 14, 2013 9:11 pm

Remember, many of those pieces are not needed! (indicated in lower case between asterisked lines.

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.

Tom McCarthy
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Re: FAQ - Mechanical Pump - Diffusion pump?

Post by Tom McCarthy » Fri Jun 14, 2013 11:57 pm

Yes, I got that. I hadn't even heard of a ball valve, I didn't understand the placement of the valves between the pumps and thought it was just a "foreline trap" that you would use, not a micro maze or oil trap.

But after your post there that's a great help and the two hours spent looking up the parts tonight...

Maybe there could be some more mention of those parts in the new schematic for the fusor for the newbies? (Im not far of being a newbie myself).

Tom

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Richard Hull
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Re: FAQ - Mechanical Pump - Diffusion pump?

Post by Richard Hull » Mon Jun 17, 2013 2:44 pm

The ball valve is mounted in a "T" fitting in the foreline and not inline within the foreline, such that when opened it will act as an "up to air valve", This valve and "T" are cheap and can be found at any good hardware store. This valve is forever left closed. The only time it is ever opened is to release all vacuum from the foreline and forepump body. All this assumes that all other valves are locked closed before doing this.

In short, it is the last thing you do after shutting all valves following a fusor run and done the instant you turn off the foreline pump. Once opened it will return the foreline and roughing pump to atmosphere. The valve is immediately closed after opening it for a second or two and left shut until the next time you have run and shut down the system.

I, personally do not have such a valve in my system. Instead, I have an easy to reach KF fitting on the pump inlet and the instant I shut off the mechanical foreling pump, I loosen the KF clamp pull it off and tilt the fitting to let in outside air, then immediately reconnect the fitting and clamp to seal the line again.

Needless to say, as the foreline and pump body are at air pressure, when starting up again turn on the foreline pump and let it run a few seconds to drag the foreline down to it lowest pressure and only then open the bellows valve to the foreline trap.

Good vacuum running and operational technique can keep a system clean and in need of little maintenance.

Few fusioneers use a foreline trap or a diffusion pump oil trap. They are just not needed for fusor work provided you use a silicone or pentavac diff pump oil. These "extras" are used more often by a vacuum purest or someone using the system for projects requiring much deeper vacuums than the fusor would ever demand.

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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Re: FAQ - Mechanical Pump - Diffusion pump?

Post by Troy Peterson » Tue Jun 18, 2013 8:15 am

For venting the foreline on my system I use an "Up to Air vent valve" from Lesker.. It's rather expensive for what it does, but it works well. Previously I was using a common hardware store ball valve for the purpose but I always suspected that it was the cause of one of my phantom leaks.

http://www.lesker.com/newweb/valves/gas ... cfm?pgid=0

Cheers,
Troy.

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Chris Bradley
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Re: FAQ - Mechanical Pump - Diffusion pump?

Post by Chris Bradley » Tue Jun 18, 2013 4:56 pm

For venting the foreline, you can also drill a small hole in a blanking disc, located at some convenient joint, and stick a bit of sticky tape over it. You can even do likewise on the neck of a KF flange joint, works equally well.

1 inch of sticky tape usually weighs in at a slightly cheaper cost than a valve. ;)

---> viewtopic.php?f=25&t=3952&p=25258#p25258

[Link added..]
Last edited by Chris Bradley on Tue Jun 18, 2013 5:22 pm, edited 2 times in total.

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Richard Hull
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Re: FAQ - Mechanical Pump - Diffusion pump?

Post by Richard Hull » Tue Jun 18, 2013 4:59 pm

When I used a ball valve on Fusor III I repacked it with vacuum grease and it sealed fine. I had a brass type valve and chrome steel ball. Thus, it could be repacked fairly easily.

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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