Mechanical Seal Selection

[dfly9891]

I need to select the material for an oring that will provide the best seal with minimum leakage for helium gas at 500 psi. What do you recommend? Buna-N? Vittol? Other?

 

[israelkk]

At what temperature range?

 

[EngineerTex]

Check out Parker. Great products, but the most useless website on the internet. Here's a link to an applications manual that includes info about helium permeability. On page 19, they recommend that you lubricate the o-ring prior to use and there's info on that in here. On page 28, it shows what materials can offer what types of permeability.

http://www.parker.com/docs/Parker.com/Literature/Section III.pdf

Also read the section on explosive decompression. With helium, it's almost a guarantee that you will have a problem. Control your rates of pressure release to address this problem.

Engineering is not the science behind building. It is the science behind not building.

 

[Garymx]

If the helium temperature is less than 80 degrees ºC you can use Viton (FKM)with double PTF wrapped.

 

[dfly9891]

Helium is at room temp.

According to Parker Orings Handbook, polyurethane offers the lowest diffusivity. I've summarized it in the chart below for your convenience (all entries at room temp and tested by Parker).

What is meant by Viton with PTF wrapped???

Do any of you have experience with polyurethane orings???


Polyurethane (P0642-70) 3.6 x 10^-8
Butyl (B0612-70) 6.5 x 10^-8
Neoprene (C0557-70) 6.5 x 10^-8
Nitrile (Buna-N) (N0674-70) 8.0 x 10^-8
Fluorocarbon (Vitol)(V0747-75) 12.7 x 10^-8


Thoughts?

 

[flexibox]

I would consider Aflas AF69/90 which will protect you from Explosive decompression. see below:

Description
AF69/90 is a highly-developed synthetic rubber based on Aflas® FEPM polymer from Asahi Glass. James Walker compounds this grade for good RGD resistance with wide chemical compatibility.

Special features

Good rapid gas decompression (RGD) resistance.
Resistance to oils, lubricants and some fuels approaching that of fluoroelastomer dipolymers.
Excellent resistance to steam, amines, bases and hydrogen sulphide.
Aflas® compounds exhibit the best radiation resistance of all elastomers.
Temperature capability
From +5°C (at atmospheric pressure) to +205°C (+41°F to +401°F).

Typical physical properties for AF69/90

Hardness: 88 IRHD
Tensile strength: 23MPa (3336psi)
Modulus @ 50% elongation: 11MPa (1595psi)
Modulus @ 100% elongation: 21.4MPa (3104psi)
Elongation at break: 115%
Low temperature torsion modulus T70: +5°C (+41°F)

Compression set: 24 hours @ 175°C (347°F): 17%
Compression set: 24 hours @ 200°C (392°F): 19%

 

[Garymx]

Check out Burgmann.

http://www.burgmann.com/?infopoolWerkstofftabelle

And you can get Design Manual from Burgmann at

http://static.scribd.com/docs/1we1icvpfc1rf.swf

On page 14th you can find all the info about the helium

Maybe It can help you.

 

[EdDanzer]

Hydrin may be your best choice.

http://www.zeonchemicals.com/hydrin

Ed Danzer

http://www.danzcoinc.com

http://www.dehyds.com