Sealing Thread

[Helepolis]

Hi,

I need to design an unpressurized container for a liquid.
My take on it is using a tube/pipe (either from metal or polymer), cut it to length (according to required volume) and seal one end with a screw-on cap.
I want for the thread to be cylindrical/parallel and use a soft seal method (I'm guessing that metal seal edge will be pricey in terms of surface machining).

I was wondering to what i need to pay attention for it to work, any thumb rules or specific thread type (anything else)?

Best,
SD

 

[robertib]

I can tell you from experience that we have used BSPP thread, and used Loctite 5331 to seal on the thread - it's easy to use, low cost, effective & the seal can be broken & replaced with minimal effort.
Otherwise, you are looking at using an o-ring, which requires precision machining to ensure correct compression in the groove.

 

[MJCronin]

There are limits to a BSPP screw-on type pipe cap...

What is the expected diameter of your container ?

MJCronin
Sr. Process Engineer

 

[Helepolis]

Apologies for the long response time.

I can tell you from experience that we have used BSPP thread, and used Loctite 5331 to seal on the thread - it's easy to use, low cost, effective & the seal can be broken & replaced with minimal effort.
Otherwise, you are looking at using an o-ring, which requires precision machining to ensure correct compression in the groove.

Thanks for the advice, but i prefer to avoid any locking substances (incompatibility and contamination issues).

There are limits to a BSPP screw-on type pipe cap...

What is the expected diameter of your container ?

The OD of the container will be somewhere in between 90-130mm.

 

[hydtools]

Put a pad of elastomeric material in the cap such that when assembled to the pipe it makes a seal between the cap and pipe end. Somewahat like a face sealing washer.

Or a hole plug instead of a cap.

https://www.mcmaster.com/rubber-hole-seals/expandable-tapered-plugs/

Ted

 

[EdStainless]

Using a ring of compressible material in the cap is easiest, then you just need a good clean flat face to seal against it.
When you select a material though make sure that it is really comparable with your fluid.
Soak samples at a warm temp, like summer time 30-40C for a couple of months. Make sure that there is no swelling, shrinking, softening, or hardening.
Getting the correct compression is needed, too much is as bad as too little. Some testing is needed and you may want to make a hard stop to prevent over tightening.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy

 

[MintJulep]

A whole universe of already designed solutions for this. Pick one that meets your needs.

https://www.mcmaster.com/pipe-caps/pipe-and-pipe-fittings/plastic-pipe-and-pipe-fittings/

 

[btrueblood]

My favorite cap seal is something like an SAE o-ring boss. 2nd favorite looks like the o-ring gland seal on most aluminum flashlight bodies. Get a copy of the Parker Oring Handbook (online pdf versions are easily found on the interwebz), it answers a lot of questions.

 

[desertfox]

Hi

You could try a BSPP thread and use PTFE tape on the male thread to create a seal.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[Tmoose]

https://www.lowes.com/pd/Charlotte-Pipe-4-in-x-4-in-x-4-in-dia-Cap-PVC-Fitting/3133059

 

[hateMech]

We really need more info about the application. The more details you give, the better advice you'll get.

If it is fine to seal it permanently, why not simply weld it? It should be more that enough for an unpressurized container.
You mention contamination, so I'm guessing corrosion might be an issue?

Like I said, more details required.

In terms of cost, I don't think a non-sealing thread and a machined surface for an o-ring would be expensive. Any decent workshop with a turning machine could do it.

 

[DAVIDSTECKER]

Take a look at JIC or SAE "O" ring hydraulic fittings.
You can get Pipe thread adaptors and Line Caps that seal and do not require sealants or lockers.