Teflon Tape and Vacuum grease

Every fusor and fusion system seems to need a vacuum. This area is for detailed discussion of vacuum systems, materials, gauging, etc. related to fusor or fusion research.
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Jake Wells
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Teflon Tape and Vacuum grease

Post by Jake Wells »

I keep reading in this forum that the use of teflon tape and vacuum grease is poor. What would be a better substitute for this?
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Noah C Hoppis
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Re: Teflon Tape and Vacuum grease

Post by Noah C Hoppis »

I've seen JB weld used well before, Just make sure it isn't directly connected to high voltage or in the way of plasma
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Jake Wells
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Re: Teflon Tape and Vacuum grease

Post by Jake Wells »

I dont want to glue my swagelok fittings. What is the best way to seal fittingsgas and comprewssion?
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Jim Kovalchick
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Re: Teflon Tape and Vacuum grease

Post by Jim Kovalchick »

You should never use Teflon or a sealant on a swagelok fitting. That is NOT how they work. The threaded portion of a Swagelok is only for bringing the real seal surfaces together. Also, Swagelok is just fine for fusor relevant pressures. Deep vacuums will require something better like VCR, but our chamber gets to 10-7 torr with liberal use of Swagelok. Improper use of Swagelok will give well deserved leakage. Use the right fitting to match your pipe material. For example, don't use a brass Swagelok on stainless tubing and expect it to work. You may get lucky but you may also make a mess. A spinning brass ferrule on a stainless tube is a sure sign of improper use. You also need to pay attention to how the fitting is et and torqued. Following the manufacturer instructions is important. They recommend a spacer of a specified thickness to ensure proper torque.

There is nothing wrong with Teflon for pipe thread sealing. White Teflon is for water. Use the yellow kind for gases. Keep it out of the flow area.

There is definitely nothing wrong with vacuum grease. It is used for resilient seals like o-rings and gaskets. It also works fine on a bell jar seal. Use it sparingly. Avoid getting it in parts of your chamber exposed to plasma. Avoid silicon based greases. I like Apiezon M or L. Vacuum grease is not for conflat seal surfaces.
Jake Wells
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Re: Teflon Tape and Vacuum grease

Post by Jake Wells »

I have a regulator.
I will use a stainless steel 3/8" compression-1/4" NPT adapter
[imghttp://cdn.mscdirect.com/global/images/ProductImages/3215192-23.jpg][/img]
then I will use a 1/4" NPT- 1/4" VCR fitting
Image
then i will conect my VCR fitting to my VCR hose. Will this be an okay setup or will this leak?
“The day science begins to study non-physical phenomena, it will make more progress in one decade than in all the previous centuries of its existence.”
― Nikola Tesla
Jake Wells
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Re: Teflon Tape and Vacuum grease

Post by Jake Wells »

I have a regulator.
I will use a stainless steel 3/8" compression-1/4" NPT adapter
http://www.mscdirect.com/product/detail ... PLA+-+Test
Image
then I will use a 1/4" NPT- 1/4" VCR fitting
http://www.ebay.com/itm/NEW-CAJON-SWAGE ... 35dba3de7d
Image

then i will conect my the fittings to my VCR hose. Will this be an okay setup or will this leak?

FORGET MY LAST SLIDE IT WAS A MESS UP AND I FORGOT TO DELETE IT!!!
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Dennis P Brown
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Re: Teflon Tape and Vacuum grease

Post by Dennis P Brown »

Teflon tape is used to allow easy disassembly of parts - not generally needed or wanted for vacuum connectors with a few exceptions (such as pointed out for NPT interfaces - than it is both useful and needed to prevent galling and/or seizing.) Swagelok connections work well even for high vacuum without tape (teflon tape is really useless in this application.) Vacuum grease should generally not be used in any high vacuum application - really - the exception is with scratches on metal surfaces that use O-rings. Then you wipe a tiny bit of high grade (read expensive) vacuum grease on the O-ring and with a lint free cloth, wipe it all off. The trace amount left is all that should be used. If the surface still leaks, it needs to be either re-machined or replaced. Never use large amounts of grease. Epoxy is a once only, never disassemble use - bad idea for expensive SS connections but very useful for cheap, low-grade (like brass/copper) compression fittings/tubes.
Jerry Biehler
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Re: Teflon Tape and Vacuum grease

Post by Jerry Biehler »

Teflon tape is fine. you can also put some red glyptal over the threads to seal them up.

For grease I use Krytox LVP. It's not cheap but works well and is totally inert. It is even safe for oxygen use.
RealBorg
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Re: Teflon Tape and Vacuum grease

Post by RealBorg »

My personal tip for sealing vacuum connections is "Thinking Putty".

While not a perfect sealant (outgassing) it is cheap and has high enough viscosity to be wrapped around any connection suspected to be leaking.

Tom
David Kunkle
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Re: Teflon Tape and Vacuum grease

Post by David Kunkle »

What about Loctite 290? Isn't he asking what to use on the threads of the fittings?
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Rich Feldman
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Re: Teflon Tape and Vacuum grease

Post by Rich Feldman »

Jake Wells wrote:I dont want to glue my swagelok fittings. What is the best way to seal fittingsgas and comprewssion?
Jake,

Do you now understand that swagelok (or other compression) connections need and want no sealant?
Not on the ferrules, nor on the nut threads. I suppose the nut threads could use a threadlocking compound if subject to intense vibration, but they are not a gas leak path. A sectional drawing will show you why.

As others have pointed out, your 1/8" or 1/4" NPT taper thread joints _do_ need something added
to plug helical gaps at thread crests and roots, even if the threads are perfectly formed, and (depending on the metals) to suppress galling of the mating surfaces.

-Rich

p.s. long ago my employer was shipping water-cooled equipment that used garden hose threads in coolant connections. Poorly trained assemblers were putting Teflon tape on the garden hose threads!
(Which, in true American style, have pitch diameter of 1 1/16" and thread pitch of 11.5 TPI.)
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Re: Teflon Tape and Vacuum grease

Post by prestonbarrows »

Swagelok will work pretty well for vacuum. Not the best, but fine for fusor levels. They are prone to developing leaks after you re-attach them a few times or bump the tubing. VCR fittings (also made by the swagelok company) are not much more expensive and are specifically designed for vacuum. They are fully reusuable and good up to UHV levels.

Teflon taped NPT will work for fusor levels if care is taken, but is not ideal. Hysol 1-C is one of the best/cheapest UHV epoxies available for sealing small leaks.

Vacuum grease should really only be a last resort. It is only used for elastomer o-rings, not threaded fittings. Rub some on the o-ring (not the groove) then wipe off all excess; if you can see any, you have too much. Then, assemble as normal.
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Chris Bradley
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Re: Teflon Tape and Vacuum grease

Post by Chris Bradley »

I did not see anywhere in the OP that the intention was to subject these fittings to vacuum.

Appears to be simply gas fittings.

If you are using a fitting for its intended purpose, follow the guidelines for its use. Simple.

If you are using a fitting for a contrary amateur purpose, the only real way to see if it is adequate for your purposes is to use it for the purpose and see if it works.

Some threads are designed to create a 'seal', others are not. You need to follow guidelines for their usage, if you want to play it safe.
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