Swagelok compression fittings

[Bogdan G B]

Are they OK to use in vacuum?

I am thinking they have the potential for virtual leaks.

[Roberto Ferrari]

Hello
Swagelok has a special vacuum line, VCR fittings.

My experience with standard Swagelok fittings (SS) is good.
No virtual leaks but they will not keep a high vacuum along many days.
Regards

Roberto

[Jim Kovalchick]

VCR fittings are definitely better for high vacuum, but they are expensive and difficult to customize to specific piping configurations because they require welded tube fittings or using pre-sized ones. Swagelok's compression fittings are much easier to work with and can be opened up and reconnected over and over again. With VCR fittings you may have to replace the washer portion if you open the fitting. For fusor vacuum conditions, you definitely can get away with compression fittings, but if you want to use your chamber and fittings for other experiments that need ultra high vacuum go with VCR. You will get sticker shock though.

[Jerry Biehler]

Standard swedgelok fitting are used in UHV all the time, though more in permanent situations. If it needs to be demountable you will find VCRs or VCOs.

[Bogdan G B]

Well, I will go with the standard compression fitting.
Even if I want to do experiments below 10^-6 torr (or something like that) I don't think I want to flow gas at that pressure, so I can use a isolation valve to completely isolate the needle valve and the associated fittings.

Thanks

[Richard Hull]

Both fusors III and IV have used only swagelock standard fittings. They seem OK from my point of opeartion.

Richard Hull

[Carl Willis]

My thoughts on Swagelok tube fittings: By design they do not have a virtual leak problem. They make a reliable leak-free seal on their first use, but on subsequent seals, your mileage may vary. If your system will use a few such connections, go for it--they are inexpensive compared to VCRs or Cajon vacuum compression fittings. But if you are going to have more than a handful, you probably want to consider the alternatives. The 1/8" and 1/4" sizes are more reliable on multiple uses than the larger sizes. My rule when I worked for the particle accelerator company was to always totally replace the ferrules and tubing when a Swagelok assembly needed to be broken down and made up again.

-Carl

[Bogdan G B]

It's good to hear that.
I will only have the the NW to 1/4 compression adapter and one (or two in series, depends how well I can control the flow) needle valve.

Yes, all my fittings are viton (NW or ISO) and I'm far beyond the point where I can chance that.

I'm going to go for a SS-4BMG series needle valves. One or two in series, maybe also a flow restriction.

I had some success with hypodermic needles, pinched real hard, I was able to reduce the pressure in my chamber to about 40microns while flowing gas, with only a mechanical pump running.

My last valve ( I posed about it here) however was not too great. It didn't really block the flow when closed.
Also I didn't like the design, a simple o-ring seal on the moving actuator, compared to the bellow seal on SS-4BMG valves.

[George Schmermund]

I've been using Swedgelok fittings in vacuum plumbing for many years now. Since my systems aren't typically baked, the fitting can be modified to produce a very reliable demountable joint. The method I've contrived will allow for a helium tight joint that requires only hand tightening.

Here's how it works. The fitting is dissembled and the 2 ferrules are removed.
The small ferrule can be set aside as it won't be used. The larger one is rotated 180 deg. and slid over the tubing in the opposite manner from the usual assembly. After placing the nut and inverted cone onto the tubing, a snug fitting o-ring (of any material you choose) is then slid over the end of the tubing. The arrangement can now compress the o-ring into the sloped recess of the fitting and then tightened. I've had unusually good results when using this method to connect glass-to-glass as well as glass-to-metal tubing.

[Jerry Biehler]

Basically you are turning them into Ultra-torr fittings.

http://www.swagelok.com/products/fittin ... tings.aspx

[aka47]

That sounds useful.

There is a guy with a glass blowing web site that does a lot of stuff and uses a similar technique. But using standard brass compression plumbing fittings.

http://www.teralab.co.uk/Glass_Blowing/ ... _Page1.htm

It could prove useful for would be experimenters living in parts of the world where stuff is hard to get.