Pneumatic gate valve trouble shooting

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Ameen Aydan
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Pneumatic gate valve trouble shooting

Post by Ameen Aydan » Tue May 29, 2018 4:30 pm

Hello,

After some searching for components to build a fusor, I came across the problem. The gate valve that I want to use between my diffusion pump and chamber is pneumaticaly controlled and I don’t know how to set that up. My original intention was to use a manual valve, however those are way to expensive for me. So I went on the internet and found that you need a solinoid that has to be hooked up to the actual valve. Here is a link to one:

https://www.idealvac.com/product.asp?pid=6193

How would one go about setting this up? How do you control the opening and shutting of the valve? Do I need any extra components (other than a compressor)? How do you make it work?!?!?

It is very hard to find literature of the valve that I want to purchase, especially when I can’t find the company website.

Here is a picture of its model#:

https://drive.google.com/open?id=1kYl-a ... E2jrSqWg1E

Please anything about this would really help.

And no I can’t use a bellow valve because the diffusion pump has a 9” inlet and i would need to buy a zero length iso reducer. I’m not doing that.

Michael Bretti
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Re: Pneumatic gate valve trouble shooting

Post by Michael Bretti » Tue May 29, 2018 6:59 pm

The link that you posted answers your own question. The page tells you exactly how to set one up, and even provides a detailed diagram how to connect it and operate it. I would say you should really do more thorough research before purchasing any components at this point. It will save you a lot of money and difficulty in getting your system operational. Operating a pneumatic valve is trivial, and this type of pneumatic control solenoid is a very standard component in pneumatic circuits. You should be able to find a massive amount of info for these types of valves on Google. Normally when I post a response I link to websites, datasheets, and research papers for reference on more advanced topics, but this is something that can be found in a few seconds of searching, and is a rather basic valve that enjoys uses well outside high vacuum technology. In addition, you can find these for way cheaper on eBay that functions exactly the same. Note that pneumatic valves are either all the way open or all the way closed - there is no in-between, and you will not be able to throttle your system for fusor purposes.

In addition, what type of chamber do you have? If you are not looking to go to UHV levels then you can easily design an aluminum o-ring adapter plate to fit between your diffusion pump and the inlet to your chamber. Best if you can find someone who can help you machine the plate if you do not have the experience or tooling to do it yourself. I am designing several chambers, all of which employ a custom aluminum adapter plate between the pump, baffle, and chamber, and is saving me a huge amount of money. Diffusion pump inlet size should not make any difference if you can make the plate yourself.

Also, do you mean a 9" inlet or a 9" diameter (OD) flange? There is a major difference - both of my diffusion pumps have 9" flanges, and the inlet is 5-6". As is they require 850W and 1450W respectively. If you really have a 9" inlet, that is an excessively massive pump that would require at least a couple of kilowatts for the heater alone, not to mention a pretty substantial cooling system and a very large charge of diffusion pump oil. With an inlet that big, you would absolutely need a water cooled baffle or large angle baffle at minimum otherwise your backstreaming and contamination will be excessive.

Ameen Aydan
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Re: Pneumatic gate valve trouble shooting

Post by Ameen Aydan » Tue May 29, 2018 7:41 pm

hello,

I would like to first start off by saying don’t worry, I did not purchase any parts yet. I'm still designing the system in fusion 360 to make sure that I revise every component rather than worry about it later when I buy the system components. Im going through a process similar to what you where doing.

As for the gate valve, thank you that was a real eye opener. I’m not very familiar with pneumatic systems which is why it was so hard to find information about the gate valve.

The diffusion pump I plan on using has a 9” OD flange... sorry. From what I caught, it is about 2 1/2’ tall, so I imagine it is going to consume some amount of watts. Also, the pump comes with a cryogenic baffle for LN2, which is perfect for back streaming.

As far as the gate valve goes, I did not know that pneumatic gate valves only open and close, I thought it was adjustable. I understand that you can use aluminum to create an adapter plate, but if I hook up a small bellow valve, it will decrease the speed and efficiency at which the pump works... I think (probably wrong).

Ameen

MatthewL
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Re: Pneumatic gate valve trouble shooting

Post by MatthewL » Tue May 29, 2018 8:03 pm

If you have not already purchased the pump, then I would probably look for a slightly smaller one. Large diffusion pumps require large backing pumps, and lots of power, oil, cooling, etc. Sadly large pumps are also usually the least expensive because the are less-desirable for the amateur experimenter. A much smaller used one will most likely be cheaper and easier to handle in the long run after getting oil, creating a cooling system, and finding a backing pump. You could also look into butterfly valves. They are not the best at throttling, but I was able to use mine to do fusion. Butterly valves can probably be found in larger sizes than bellows. If you use a small bellows valve on a large pump, then the pump will not be operating as it could. It would be far better to use a bellows valve on a small diffusion pump (preferably air cooled, although not necessary).

-Matthew

Michael Bretti
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Re: Pneumatic gate valve trouble shooting

Post by Michael Bretti » Tue May 29, 2018 8:08 pm

Excellent to hear that you are using some cad software to plan everything out in advance. I also use fusion 360 myself, and have found it invaluable. Sounds like you are on the right tracking for planning out and designing your system, and I highly encourage everyone to take this similar approach.

For the gate valve, just picture it like a pneumatic piston or cylinder. It works exactly like that (it literally is just a pneumatic cylinder on the inside), except at the end it is actuating a circular plate that seats to close the valve. But you would drive and operate it the same as any pneumatic cylinder. All of the same principles apply. Unfortunately, they are only open or close, but for some reason they are much cheaper on eBay than manual ones, and generally much more available.

Do you have the model number for the diffusion pump? Do you have any pictures of the pump, or are there any labels on it? If you do, that is certainly something I could look into and help find a datasheet of specs for. The more you know about the pump you are using, the better off you will be.

If you have a cryogenic baffle already made for the pump, then you are in good shape. Something like that would allow you to go to much deeper vacuums than without it or just using a water cooled baffle. Of course liquid nitrogen adds some extra cost, but even having the baffle in place will help a bit with backstreaming.

You are certainly correct that a small valve attached to a large pump inlet will choke the speed and decrease the pipeline conductance. It really depends what your goals are for your system, and how the rest of your system is designed. Do you have any preliminary designs, cad models, or pictures of your system and components? I could provide much better answers and give better direction knowing more of how you are looking to lay out your system and what components you have and/or are planning on using. For example, on my small system, I do go from a large inlet to a 2.75" conflat, which greatly restricts speed, but I made my pumping pipeline as short as possible to maximize conductance for its size. Unfortunately, it is the only pump that I had, so I had no choice but to find a way to mate them together. However, between my very first design and my final design, I was able to more than double the effective pumping speed with proper component selection. Remember, the ultimate effective speed of the system is limited to the lowest conductance component. So even if you have a massive valve, baffle, and pump, if you are still going to a very small inlet chamber, your speed at the chamber will never exceed the speed of that choke-point, which in that case, would be the chamber inlet.

Michael Bretti
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Re: Pneumatic gate valve trouble shooting

Post by Michael Bretti » Tue May 29, 2018 8:31 pm

One possible benefit to consider of having a large diff pump vs a small one. While small ones have lower power requirements and easier to work with, a larger pump does have the benefit of higher speed, which could allow your system to handle more. For example, if your diff pump speed at your operating pressure for deuterium is 100 L/s, your total system conductance is 50 L/s, then your effective system speed is:

Seff = Smax*C/(Smax+C)
Seff = 100*50/(100+50)
Seff = 33 L/s

However, if you use a larger pump with let's say 200 L/s now, then your Seff = 40 L/s. While it looks like a small gain, it is a gain of 17.5% speed, which for high vacuum levels is an appreciable amount (in molecular flow). For a standard fusor operating in transitional flow, at lets say 0.01 torr, this may have less of an impact. However, if we want to determine the ultimate gas load, assuming a perfect ideal case with no other loads other than deuterium, your gas load changes from:

Q=SxP
Q=33*0.01 = 0.33 torr*L/s
Q=40*0.01 = 0.40 torr*L/s

Converting this to sccm (for flow rate of deuterium gas), your system will increase flow rate handling from 26.4 sccm to 32 sccm. Maybe not a huge difference, but it gives you more room to play with, especially when in real life you need to factor in other gas loads such as permeation, leaks, backstreaming, water vapor, etc. Then these numbers really start to become important, and any boost you can get in pumping speed can help.

Rex Allers
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Re: Pneumatic gate valve trouble shooting

Post by Rex Allers » Tue May 29, 2018 9:43 pm

I'm surprised that there hasn't been mention of how (not) practical a pneumatically actuated valve might be for controlling the vacuum into a fusor chamber. Per Richard's descriptions in the FAQs for operating a fusor, normally the valve controlling the vacuum will be barely cracked open while doing fusion. It is a big part of controlling the pressure in the chamber and the flow rate of deuterium.

The pneumatic actuators are designed for either fully open or fully closed. If you carefully regulated the actuating pressure you might get the valve to some partially opened mode, but I doubt you can get the level of finesse or repeatability you need.

There's some possibility you could convert the valve to some kind of mechanical pulling open. That would depend on getting to the innards of the actuator cylinder and fabrication skills of designing something.

As with other comments about the sizes of things you are looking at, these big things do sound undesirable.
Rex Allers

Dan Knapp
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Re: Pneumatic gate valve trouble shooting

Post by Dan Knapp » Tue May 29, 2018 10:09 pm

A cheaper solution is to use a manual valve. I bought one on amazon for $10 (Baomain Manual Hand Lever Control Valve 4H210-08 G1/4" Air Inlet 5 Way 2 Position). The valve has 1/4 NPT fittings. I used 1/8 Swagelok to 1/4 NPT adapters and 1/8 plastic tubing for the air lines. Rather than tie up a compressor, I used a Harbor Freight portable air tank (29.95 regular price; catch it on sale for less and use a 20/25% off coupon; don't forget to take your free meter coupon!).
The problem with using a pneumatic gate valve as your main chamber valve is that there is no easy way to use it partially open for controlling pressure. I found that even a manual valve on my main chamber could not be used to throttle pumping for pressure control (there was no fine control on sealing), and I had to add a bypass line with a bellows valve. Another tip - if you use a bypass with bellows valve, be sure to connect the bellows valve so the o-ring sealed face of the valve is toward the pump (opposite of how you would normally connect to a chamber). If you connect the normal way, it is more difficult to regulate the pressure because you have the higher vacuum (pump side) pulling on the bellows, which tends to try to close the valve.

Jerry Biehler
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Re: Pneumatic gate valve trouble shooting

Post by Jerry Biehler » Thu May 31, 2018 6:21 am

Whoa, stop. This is a 6" ~2000l/s diffusion pump. Way, way to big for a fusor.

Pneumatic gate valves are binary, open or closed, there is no in between. Technically you could only close them part way but it is going to be random where it stops. And even with controllable valves that will fit an ASA6 flange they have limited minimal conductance that will still be more than what you want.

Go and find a small diff pump.

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Richard Hull
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Re: Pneumatic gate valve trouble shooting

Post by Richard Hull » Thu May 31, 2018 7:07 am

Again, Jerry nailed it.... A 2"-4" diff pump throat is about as big as you will need. An ideal is about 3". A 9" throated diff pump will cost a small fortune to "oil up". As mentioned in other posts, you will pay more for a smaller diff pump, assuming it is in fine condition. This is simply because those with an operation that would benefit from a 9" diff pump will get a Turbo rather than leap back into the 1950's with a monster diff pump. Such a big diff pump is a virtually un-sellable item to all, but the "vacuum ignorant" and megalomaniacs who think bigger is better.

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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