Sealing threads and preventing backout 1

[HRP21]

Gentlemen,

I am trying to seal the fitting on the body (please see attachment). I do not have any restrictions on the type of threads. But I want to lock the fitting in the body such that it cannot turn by itself with vibrations ( so that it starts leaking). I do not want to make any extra holes in the body except for main threads. Is there anyway I can jam the fitting in the body but should be able to take it out if I need to. (without damaging the body).

(Side note- It need not be threads can be anything else unless it seals and does not leak and does not back off).

Thanks for all your suggestions.

HP

 

[Hidromar]

Hello!

I know there's a kind of chemical seal that can lock threads without damaging the hardware.

It doesn't damage the hardware, but, when trying to take if off you will be very upset!

http://www.hidromar.es

 

[flexibox]

HRP 21 I have attached a hand sketch that I hope is of some help to you. I think I undrstood your sketch correctly. By using NPT threads and ensuring they are drilled and tapped correctly then you should have no problems (not Jamming) sealing the fitting and removing it as an when required. Use some PTFE tape to prevent leakage and lubricates the threads to allow you to remove the fitting frequently.

PS: I assumed this will be between 1/2" or 3/4" connections. If this is 2" in SS be careful of gauling.

Good Luck !!!

 

[HRP21]

Thank you Hidromar and Flexibox.

Flexibox, thats the line was I was thinking on. But we want something like a jam nut/ lock nut that would prevent the fitting from turning because there will be another fitting (fitting 2) inside this fitting (fitting 1) which has to to be removed frequently. (see attached)

 

[Hidromar]

Hi!

In that case, I still think a chemical seal will be a good option. I didn't have any knowledge about working with these ones, but, up to I heard, if you don¡t have special sealing requirements and/or high pressure, it works fine.

http://www.hidromar.es

 

[flexibox]

Try using standard swagelok fittings like VCR® Metal Gasket Bodies Straight P/N SS-12-VCR-7-12. You may find standard fitting which you can modify. Call your local swagelok representative for advice.

 

[tr1ntx]

HRP21,

You're first sketch says the threads can be UN, and you say you want of a jam nut, so why not use a jam nut? If needed and the space is available, you could machine 2 flats on the top end of fitting 1 so you could use a wrench to keep it from turning while you jam the jam nut.

Fitting 1 doesn't have to be threaded all the way up does it? If not, you could machine it from hex bar, then you would have a hex at the top.

 

[HRP21]

Tr1ntx,

I cannot use the jam nut directly because the UN threads won't seal. So I have to find a way to seal it as well.

And using the jam nut on fitting 1 will not prevent it from turning open when I opening fitting 2.
So I have to find a way to seal fitting one prevent it from cracking loose while I remove or insert fitting 2.

 

[Hidromar]

Hi!

Just wondering. I understood you didn't like to use a new nut.

If this is not the case, why not use a rubber-to-metal bonded seal or, alternatively, an O-Ring plus a spacer, and then a nut clockwise or counter-clockwise to retain the main "axe"?

http://www.hidromar.es

 

[kevindurette]

How about an o-ring seal below the threads? Putting the o-ring on its own shaft would prevent extrusion through the threads. The installation chamfer is important here too.

Durette

 

[1gibson]

How about a flat rubber gasket on the bottom face? Add some lubrication to the face of the fitting so it doesn't stick when it contacts the rubber.

1) When tightened all the way the compression of the rubber will act similar to a lock washer, may also damp vibration
2) The rubber will seal at the fitting/housing faces once the fitting is all the way down

I say "rubber" but silicone or even fibrous gasket material could work depending on pressures. Maybe a PTFE disk. Plan on replacing the gasket fairly often depending on material. Vary the thickness and material/durometer of the disk to obtain both sealing and "lock washer" properties.

If not a disk, might be able to obtain similar face-face sealing with very robust o-ring (PTFE or similar)

 

[DesignerGuy16]

Have you thought of anything like a JIC or SAE-ORB sealing method? These are typically used in higher pressure applications and should give you a tighter seal than your standard NPT.

The SAE-ORB fittings should handle vibration a little better than NPT because it gives a flexible seal that can disperse some vibration compared to thread to thread and no barrier.

The above idea from 1gibson is also good as an o-ring face seal on the bottom should give a similar effect, but you'll want to use parallel threads if you're going that route so you can assure you're sealing tight to the bottom of the hole.

James Spisich
Design Engineer, CSWP