FAQ: Vacuum line diagram v2.0

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Tom McCarthy
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FAQ: Vacuum line diagram v2.0

Post by Tom McCarthy »

This is the new diagram for the vacuum line, I've added a colour coding identification method and made the whole thing a bit easier to read and nicer to look at.
You can thank Rich Feldman for this version as it's from his tips that these improvements have come!

Also, I hope that the outlet/Inlet locations for the diffusion or turbo-pump are right. Feel free to tell me if that's wrong or anything else isn't right, any tips or things that could be added are appreciated.
Gas line diagram v1 soon to come.
v2.1: Added T-junction for ball valve/roughing pump/Bellows sealed valve connection.
Vacuum line diagram v2.1
Vacuum line diagram v2.1
Vacuum line diagram v2
Vacuum line diagram v2
Vacuum line diagram v1
Vacuum line diagram v1
Tom

Due to the fine work done here, I have edited the title to be a FAQ. R.H.
Last edited by Tom McCarthy on Mon Jun 17, 2013 4:21 pm, edited 1 time in total.
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Re: FAQ: Vacuum line diagram v2.0

Post by Tom McCarthy »

...That well and truly filled me with a feeling of joy after reading your edit Richard. Again, most of it is down to Rich's help and corrections for v1 to bring it to what it is.

Also, after your reply on the Mechanical pump - Diffusion pump FAQ today, I've realized that he foreline should be split from the start with the bellows sealed valve one way and the ball valve the other, I'll fix it as son as possible and get it up on this post.

Tom
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Rich Feldman
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Re: FAQ: Vacuum line diagram v2.0

Post by Rich Feldman »

Got tired of holding my breath waiting for someone else to respond.

The T fittings you added in v2.1 (by editing your v2.0 original post) are a step in the right direction, but you can install a trap in the foreline without using any tees. Hint: label the "foreline". Or search this forum (as I have not searched) for fusor vacuum system diagrams drawn by others.

Now how do you admit air to the intake port of mechanical pump, when it's valved off from the HV pump?
(It's bad practice to leave the mechanical pump turned off with its inlet under vacuum.)
Richard Hull told you a solution today, in another thread:
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.
Even if you do it by momentarily opening a quick-connect pipe fitting (Richard's "KF" trick -- look up KF), that fitting needs to be there. You don't want to be unscrewing a threaded joint or pulling a hose/tube off of a barb fitting.

What would be a good sequence to release the vacuum from the fusor chamber before, for example, taking it apart?

I also think the mechanical pump's exhaust port should be shown. [ edit -- I see that it is now! ]
They all have one.
People using industrial rotary-vane vacuum pumps generally put an oil mist eliminator on the exhaust.
One example is at the bottom of first picture here:
viewtopic.php?f=10&t=3977&p=25528&hilit ... ron#p25528
Some have reported using a hose to carry the oil mist somewhere else.
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Re: FAQ: Vacuum line diagram v2.0

Post by Tom McCarthy »

Just finished adding a few small things for v2.2, I've added two vents - One for the foreline and one for the chamber.
Took in what you said Rich, hope this addresses most of the issues. I also found a diagram literally a minute ago while searching the net, that is excellent. I'll attach it below.
And again, if there's anything else that can be added/fixed/labelled do tell!
Vacuum line diagram v2.2
Vacuum line diagram v2.2
Diagram found on net
Diagram found on net
Tom
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Re: FAQ: Vacuum line diagram v2.0

Post by Dan Tibbets »

Regarding relieving fore line vacuum. I have relied on unscrewing the connection - admittedly not an elegant solution. But, I also rely on the ballast valve built into the roughing pump to gradually drain the fore line vacuum (over several minutes?). Is this adequate? Any additional valve introduces the potential for leaks, so it is not without some compromise.

The other issue is that (at least in version 2.0) I see no way of roughing down the vacuum chamber without going through the high vacuum pump. If you open the chamber for any purpose you have to make sure the high vacuum diffusion pump has cooled, you cannot by pass it.

Dan Tibbets
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Chris Bradley
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Re: FAQ: Vacuum line diagram v2.0

Post by Chris Bradley »

Rich Feldman wrote:Now how do you admit air to the intake port of mechanical pump, when it's valved off from the HV pump?
(It's bad practice to leave the mechanical pump turned off with its inlet under vacuum.)
I don't see any reason for wanting to admit air at that point, if it is valved off?


Usually, what [I've always thought!!!] is to be done is to have a trap right on top of the intake port of the mechanical pump, and then a valve straight after that (which then leads to the molecular pump).

In this way, when you shut that valve, the vacuum is held in the intake port of the mechanical pump AND the trap. If you go opening that up, you contaminate the trap. To de-contaminate it, you run the mechanical pump with that valve closed.

The intake port is designed to hold a vacuum. If it didn't, it wouldn't pump??!!!

FWIW, I use an electromechanical valve between the trap and the molecular pump, with a 24V 'open' and a 5V 'sustain' operation. In this way, if there is an electrical interruption in the mains (which is not at all unknown where I am - rubbish power grid) then the valve shuts and remains closed, thus protecting the molecular pump from being exposed to the mechanical pump while it is not pumping during that electrical interruption. If one were to have the ballast valve open and the valve in the foreline fixed open (viz., a manual valve), and the mechanical pump stops momentarily (for whatever reason, mech or electrical failure) whilst it is backing a turbo, the turbo will be history.
Last edited by Chris Bradley on Tue Jun 18, 2013 1:24 pm, edited 2 times in total.
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Richard Hull
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Re: FAQ: Vacuum line diagram v2.0

Post by Richard Hull »

The net based diagram shows a roughing line. Absolutely not needed or important at all for any fusor work. You can rough through the diff pump.

How to open to air the chamber? Answer....

1.Close all valves
2. Temporarily remove small gas line.... or.... simply unbolt your chamber conflats and give a light pry up with a screwdriver at the seams. Usually, unbolting will create such a leak that by the time you are finished unbolting, the thing comes apart. Meanwhile, the diff pump is still under vacuum.

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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Chris Bradley
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Re: FAQ: Vacuum line diagram v2.0

Post by Chris Bradley »

Dan Tibbets wrote:Regarding relieving fore line vacuum. I have relied on unscrewing the connection - admittedly not an elegant solution. But, I also rely on the ballast valve built into the roughing pump to gradually drain the fore line vacuum (over several minutes?). Is this adequate?
I just don't see any reason to do this. I suppose it'd work, if you really want to vent the intake port [I still don't get why] but risks pushing vapours/oil droplets sitting above the pump oil back into the trap and everywhere that you don't want it.

One word of warning: Never shut off the pump with the ballast open.
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Re: FAQ: Vacuum line diagram v2.0

Post by Chris Bradley »

Cheapest way to install an up-to-air vent.

Works perfectly.

---> viewtopic.php?f=25&t=3952&p=25258#p25258
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Re: FAQ: Vacuum line diagram v2.0

Post by Rich Feldman »

Chris, I love your tape-over-hole trick for venting foreline.
Other inexpensive alternatives come to mind that will not lose stickyness, but can still wear out:
a tiny rubber stopper in a tapered hole, or a short bit of gum rubber tubing with a pinch clamp.

I was taught not to leave mechanical pumps turned off with inlet under vacuum, even if valved off from trap and/or foreline.
The pump chambers will slowly fill with oil, via the clearances provided for lubrication.
That creates the risk of overpressure or even hydraulic lock when the pump is restarted, especially if the two pump stages have different displacements or phases. It's been known to make press-fitted part connections slip. One design remedy is an overpressure relief valve. I got one retrofitted for free, by the factory service tech who re-pressed a rotor in my DV-85 pump.

Another practical note, to which I can personally attest:
When a mechanical pump is not right-side-up, then running the motor for even a second can discharge a full load of oil through the exhaust port.

Tom: re. the diagram "found on the net" which you re-posted. I encourage all re-posters of Internet content to carry along the attribution, or at least a source link. It's the respectful thing to do, even if original content did not have a copyright label.
Last edited by Rich Feldman on Tue Jun 18, 2013 3:02 pm, edited 3 times in total.
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Chris Bradley
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Re: FAQ: Vacuum line diagram v2.0

Post by Chris Bradley »

Rich Feldman wrote:I was taught not to leave mechanical pumps turned off with inlet under vacuum, even if valved off from the foreline.
The pump chambers will slowly fill with oil, via the clearances provided for lubrication.
OK. Thanks. I can see that is an argument that could apply to some pumps. I guess all the pumps I've ever come across have an oil distribution valve to prevent suck-back, and thought all pumps have them. :oops:

I reverse my comment - I guess if you don't know if your pump has an anti-suckback distribution valve then best assume it doesn't, and vent the intake port!!!

Just a reminder; if it's ever necessary to vent the intake port (whether for this reason, or otherwise), make sure the intake port is vented to air while the pump is running, then turn it off.
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Re: FAQ: Vacuum line diagram v2.0

Post by Rich Feldman »

Something I learned today: apparently even some fancy expensive pumps have suck back issues.

Here is an "auto-Off Safety Vent Valve", with KF flanges for inline plumbing, and third port open to atmosphere.
In the event of electrical power failure (which I suppose can happen in amateur fusor labs),
it isolates the evacuated system and vents the mechanical pump inlet.

http://www.lesker.com/newweb/valves/ven ... cfm?pgid=0
The KJL flyer says:
-Eliminate time consuming and costly cleanup of dirty vacuum lines, caused by oil backstreaming from the pump
-Small orifice in the shut-off valves vents the mechanical pump to atmospheric pressure for easy restart when power resumes
-Even when the mechanical pump is equipped with an anti-suckback valve, these valves are recommended because the pump’s integral valve will not vent the pump

In amateur systems that depend on manual sequencing of valves and switches,
it might be a good idea to plan in advance (and write down) any actions to take when power fails.
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Re: FAQ: Vacuum line diagram v2.0

Post by John Futter »

From my 35 + years of experience relying on an automatic suck back valve is asking for a diff or turbo pump filled with backing pump oil.
I have had to clean out many after this feature failed / or had a minor leak that ends up giving an expensive messy problem.

If the foreline is at atmospheric pressure the oil will stay in the backing pump.
Purists would backfill the backing line with dry N2 or similar to keep the oil clean and water free
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Re: FAQ: Vacuum line diagram v2.0

Post by Rich Feldman »

When a mechanical pump is not right-side-up, then running the motor for even a second can discharge a full load of oil through the exhaust port.
Does anybody here know how they get high vacuum for experiments on the International Space Station?
Hair_clippers_with_vacuum_device_on_the_ISS.jpg
from http://spaceinimages.esa.int/Images/200 ... on_the_ISS
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Re: FAQ: Vacuum line diagram v2.0

Post by Chris Bradley »

Rich Feldman wrote:Does anybody here know how they get high vacuum for experiments on the International Space Station?
Is that meant to be a joke?
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Re: FAQ: Vacuum line diagram v2.0

Post by Chris Bradley »

John Futter wrote:From my 35 + years of experience relying on an automatic suck back valve is asking for a diff or turbo pump filled with backing pump oil.
I have had to clean out many after this feature failed / or had a minor leak that ends up giving an expensive messy problem.
I'd never rely on the pump's suck-back valve. That'd be the job of a foreline valve.

Thing is, I have an alumina bead trap that sits right on top of my mech pump, then the foreline valve on top of that. By relying on the mech pump suck-back valve, I just leave the trap under vacuum all the time, keeps it clean. If oil were to get sucked into the intake port, or even into the trap, I can't see it'd be a Big Deal, even if it hydralocks. Open the ballast valve, wait a few minutes?

Maybe it's even happened and I've never noticed!?!? Funnily enough, the 5A fuse in the plug started blowing out every time I started the pump up, a year or so ago. After running out of 5A fuses, I put in a 13A fuse. No problem after that!! :-?

I'm asking, just because it has never really dawned on me before that it'd ever be a problem. If it could be, I'm open to hearing about any 'risks'. Not sure there are any big-ones I can see. I guess, in that sense, Dan's method to use the ballast valve, once the pump stops, is actually the most direct way to even out the in-out port pressures of the mech pump.
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Re: FAQ: Vacuum line diagram v2.0

Post by Rich Feldman »

>> Is that meant to be a joke?

My question about the ISS was perfectly serious.

We know that various microgravity experiment units, for example the Material Science Laboratory, are designed to bolt into a standard rack on board ISS.
" The crew then connects all required ISS resources, and once the solid state power control module (SSPCM) receives power, the master controller initiates an automatic startup of rack systems. "
from http://www.nasa.gov/mission_pages/stati ... operations

We can bet that the facility resources include electric power, some kind of cooling system connection, and a computer network.
How about compressed air (used widely in industrial motion control systems), or dry nitrogen ?
How about various kinds of vacuum -- must each experiment module be self-contained?
The question came up because most terrestrial HV systems include orientation-sensitive pumps. An exception might be a turbo-drag pump backed by a diaphragm pump.

Some laboratory "rooms" on ISS might have spigots for roughing vacuum, connected by lightweight pipes to "the outside", but I would not bet on it. Today I learned that the static pressure outside is usually in the 1e-8 to 1e-9 torr range. To bring that into an experimental chamber, you'd need a fat pipe and big hole in the wall right there, built to code and installed by a licensed plumber. :-)

[edit] I just found the answers myself, in this ISS Users' Guide: http://www.spaceref.com/iss/ops/ISS.User.Guide.R2.pdf
Page 20 has general specs for the Vacuum Exhaust System (Waste Gas), with 1 inch pipes in each module. It can vent a 100 liter chamber to 1e-3 torr in less than 2 hours, if nobody else is using it. Selected locations also have independent Vacuum Resource lines, guaranteed to deliver 1e-3 torr.
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Re: FAQ: Vacuum line diagram v2.0

Post by Chris Bradley »

Rich Feldman wrote: I just found the answers ... Page 20 has general specs for the Vacuum Exhaust System (Waste Gas), with 1 inch pipes in each module.
That' why I thought you were joking, with the biggest, deepest vacuum reservoir being just a few feet and a trivial bit of plumbing away.
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Re: FAQ: Vacuum line diagram v2.0

Post by Tom McCarthy »

Rich, I completely agree. Sorry I forget to do it earlier, but I had the pdf bookmarked all the same.http://microlab.berkeley.edu/labmanual/chap6/vacuum.pdf That's the pdf where you'll find the diagram I put up of the vacuum line. It's easy enough to see. There's variations of the drawing over the next 2-3 pages that give a good explanation of what valves to open/close when operating each pump.

Tom
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Re: FAQ: Vacuum line diagram v2.0

Post by Aditya Somasundaram »

Hello.
Does the valve between roughing pump and diffusion pump need to be ball valve? Or can I use other valves such as right angle valve?
Thank you!
-Adi
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Re: FAQ: Vacuum line diagram v2.0

Post by Tom McCarthy »

Any vacuum valve will do really, you're still in the "dirty" or relatively low vacuum with the roughing pump.

However, it's been a while since I originally posted that diagram and since have been advised that ball valves won't hold up to vacuum scrutiny - they might be applicable in the fore line, but I've been strongly advised not to use them in the high vacuum line. Most angle valves from MDC, Lesker, Pfeiffer etc. are rated for UHV or at least HV so they're sealed for Fusor vacuums anyways.

Hope that helps,
Tom
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Re: FAQ: Vacuum line diagram v2.0

Post by Aditya Somasundaram »

Tom,
Thanks for the response!
-Adi
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