#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 »

A quick question, if you use a fore-line trap with the required two bellows valves and a diffusion pump would you still need the connector between the mechanical pump and diffusion pump?
Also, if you are using a gate or third bellows valve to connect the diffusion pump to vacuum chamber and regulate the vacuum's "flow" would you still need the second connector?

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

Post by Richard Hull »

You will always need to connect the mechanical pump directly to the diffusion pump. Between them you can have a trap and, or, a valve, but you must connect them together.

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
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Re: FAQ - Mechanical Pump - Diffusion pump?

Post by Tom McCarthy »

So the trap accompanied by its two bellows valves will act as the connector and the bellows valve or gate you use to connect the diffusion pump to the vacuum chamber is the other connection.

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

Post by Chris Bradley »

Richard Hull wrote:... connect the mechanical pump directly to the diffusion pump.. Between them..a valve
hmm... I'm thinking that is tempting fate that someone would close the valve with the diff pump still 'on'. Messy?
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Richard Hull
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Re: FAQ - Mechanical Pump - Diffusion pump?

Post by Richard Hull »

Sorry about that. If you use an oil trap in the foreline, it needs one valve. A cold trap in the high vacuum line will need none. I have supplied an "in order" hookup with options.

Must haves items are in all caps. Optional items not needed for fusion are between asterisked lines.

MECHANICAL PUMP
UP TO AIR BLEEDER VALVE (can be a ball valve) OR KF DISCONNECT (AVOIDS SUCK BACK)
SHORT HOSE
BELLOWS VALVE

*******************************
oil trap/micro maze, etc.
bellows valve
******************************

DIFFUSION PUMP

*****************************
cold trap
****************************

BELLOWS OR GATE VALVE
FUSOR CHAMBER

There you have it.

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
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Re: FAQ - Mechanical Pump - Diffusion pump?

Post by Tom McCarthy »

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 »

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: FAQ - Mechanical Pump - Diffusion pump?

Post by Tom McCarthy »

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 »

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: FAQ - Mechanical Pump - Diffusion pump?

Post by Troy Peterson »

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

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

Post by Chris Bradley »

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 1:22 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 »

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Pascal Mueller
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Re: #2 FAQ - Mechanical Pump - Diffusion pump?

Post by Pascal Mueller »

You wrote that "You will need to get at least a 2-4 CFM, (cubic foot per minute)". I did read about several kidn of pumps and while checking ebay I did check out quit a few manuals.

What I noticed is, that e.g. for a Turbovac 50 and similar the recommended forepump is a Trivac D2.5E, the CFM really differs. How is that exactly possible? From what I've seen, the CFM from the turbo pump in the given example is way higher than the one from the forepump. I currently sturggle a bit seeing the connection between the CFM of the forepump and the CFM of the trubo/diffusion pump.

Also: Is that 2-4 CFM related to the pump which is directly connected to the vacuum chamber, right? So e.g. if I have a demo fusor with just one pump it should have 2-4 CFM but if I have a diffusion pump with a forepump, the 2-4CFM would be for the diffusion pump, right?
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Richard Hull
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Re: #2 FAQ - Mechanical Pump - Diffusion pump?

Post by Richard Hull »

A demo fusor only needs a mechanical fore line pump. A real, working fusor would normally need both a fore line pump and a diff pump. Diff pumps will not operate properly with pressures greater than a 50 micron vacuum at the inlet. The mechanical pump is needed to allow the diff pump to operate.

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
Pascal Mueller
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Re: #2 FAQ - Mechanical Pump - Diffusion pump?

Post by Pascal Mueller »

EDIT: In the original post I misread a unit, thus being off by 10e3. Added an example for clarification of my question.


Of course I already do know that. :) That's something you can easily read in these FAQs and on Wikipedia. I try to gather as much information on my own as possible but I think I might be confused here also I might have asked badly. My goal is to make real fusion at some point, the demo fusor was just an example. So maybe I ask a bit more concrete: If I have, let's say, a spherical chamber with a diameter of 8"-10" (20-25cm) I am wondering how many liters/s (or CFM) my high vacuum pump (i.e. turbo or diffusion) should be capable of. I make an example at the end.

I really though I did read some information about this in these FAQs but I was just looking through them for an hour or even longer and couldn't find it. In another thread you stated "The pumping capacity for any fusor mechanical pump needs to be at least 2 CFM for a demo fusor, but for real fusion in a really normal chamber of 6" or more, you will want something of at least 5 CFM Capacity." So 5 CFM is about 2.36 liters/second.

Example: For a 8" chamber I need at least 5 CFM according to that above.

Let's say we have a Turbo Pump which has about 50-65 l/s i.e. 105-140 CFM (depending on the gas). The recommended forepump has 3.4 m^3/h i.e 2 CFM.

Now, if you say I need 5 CFM I am more than fine since my pump has 105-140, right? I am very unsure because that example was from a pump which sees to be on the lower end when it comes to pump speed.

Thanks for any input!
Last edited by Pascal Mueller on Sun Dec 23, 2018 3:32 pm, edited 2 times in total.
John Futter
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Re: #2 FAQ - Mechanical Pump - Diffusion pump?

Post by John Futter »

pascal this should have been asked in the new user chat area and certainly not in an FAQ
Some pumps are cu metres per hour some are cu feet per minute bur with mechanical pumps it is the pump swept volume x rpm
more reading needs this one
Pascal Mueller
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Re: #2 FAQ - Mechanical Pump - Diffusion pump?

Post by Pascal Mueller »

Dear John,

wasn't sure where to post - though since I quote information from the FAQ I should ask it here.

And yeah, of course I still have a lot of reading to do! Thanks for the input and sorry for the wrong posting.
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