How to select and design an O-Ring?

Durability is the trigger going to be under continuous operation. How hot will the device possibly get. You said a personal flotation device. How long may it be in storage before use. Pressure applied. Gas being used to inflate. Materials used to make the trigger device.

In agreement with durability. Keep in mind the purpose of the o-ring when deciding what will affect durability. Some materials may not perform well if repeatedly wet/dry. Also if a pressurized gas deployment; will the temp be an issue, or temp cycling. Does it need to be airtight, watertight or both?

Damnit Ozzb, you did it again.

Oh well.

Try this site for design parameters

Thank you very much!!

I have found the Parker O-ring Handbook to be helpful in spec-ing O-ring size/materials and O-ring groove dimensions. Yes, it's going to guide you toward buying their product, but it's a good general resource on sealing applications.

jhammond

__________________________

www.patent-innovations.com

Call your local PARKER SEAL Dealer.

They will supply you with data and recommendations.

Parker has a series of free software titles called ifForm. One of them selects O-Rings. Material is selected based on chemical exposure, temperature, etc. Size is selected based on application.

You can get them from the Parker web site.

Others include accumulator sizing, cylinder design, hose/fitting selection, etc.

O' ring sealing is very effective but tricky if some salient points are not looked into:

Is it static sealing or dynamic?

The sealing surface is a 'facial' or 'cylindrical'?

Sliding or Rotary?

Unbranded, local manufactures do not ensure perfect circular cross section, oval or even worse.

When these rings are molded (unless due cares are taken) the ribs would exist at the parting surface of molds. These ribs are highly objectionable when sealing cylindrical surfaces.

O' ring groves are to be properly dimensioned. The grove depth should be lesser than the diameter of ring, such that the ring ensures the contact and not the surface. The width of the grove should be wider than the diameter of the ring, such that the grove have enough free space, even after normal loading, as to accommodate additional loading or swelling. The thump-rule: Depth = 0.7/0.8 dia, Width = 1.2/1.4 dia. For precise dimensions, better to refer the Design Data Book. Reputed manufactures (like Parker) give abounded guidelines for grove dimensions.

well mate! listen up ..if you're designing a device that you may have to depend on to save your life, you might want to contact your local coast guard office... but are you a student from a maritime academy? or studying the effects of weather & elements on a new design of PFD'S? ok you got the floor....

I'm a 'reinvent the wheel first' kind of guy (which is why its a good thing my engineering is a hobby, not a profession). Meaning - I like to think from first principles what are the constraints, demands, etc. on a part I'm designing before I go to the 'experts'.

Here's what I would think about when designing my own O-ring (most of which others have already said, but I like the sound of my own voice ):

What pressure is to be contained by the O-ring?

What MINIMUM (remember the space shuttle disaster was because the O-rings on the SRBs were too COLD) and maximum temperatures are expected? What are you not thinking about (e.g. storage in a locker exposed to equatorial sunlight for 12h/day, * 365d/y, or in the same locker in arctic regions for the same duration)?

What chemical environment must the O-ring endure? Salt water? Acidic or oxidizing vapors/gasses/liquids, catalytic reactions?

What vibrational stresses must be handled? What thermal cycles must be handled? How often? To what extremes?

What is its expected lifetime?

Will it be used in a static or dynamic (moving parts) situation? Will it be assembled once and then left, or assembled and disassembled many times (so will have to absorb abrasion, possible incursion of foreign particles (dirt, to most of us), being cut, or stretched / compressed beyond limits? Can it fall out - and if so what impact must it be able to withstand? How often?

What are the other structural materials the O-ring will be in contact with? Which is softer/harder? Can there be any electrolytic interaction - which could have consequences to other parts of the assembly (such as electrically induced corrosion, heating, attraction of dirt or chemical changes) and/or an interaction with the gas being contained?

How will you inspect the part? How can you tell if it must be replaced?

There may be other things to think about, but that's a good list to start with. Once I've thought about those things, and generated some tentative answers, only then will I go to a reference book to see what others have to say about the matter. This way, I know whether my reference sources are giving me the full picture, or whether there is something I'm completely missing that could bite me in the back later ...

yeah odessy,this was what i was thinking,i was a merchant marine engineer for 12yrs., and the elements you described are exactly what i was thinking about..especially when disaster hits and you you need it most ,i've been thru some incredible situations at sea ,E.G when the engine room caught on fire,(thank God we were only a few miles off shore i had a simple garden hose stowed proper and ready to go and it was the product of me and my asisstants who ;thought like me we were ready for the worse, but we worked for the best, and we took it as it came ...I have 100's of stories like this ,but you are right where this equip. is stowed how it is stowed has an impact on shelf life and when you need it, will it be ready to deploy..? Like walter Brennan used to say..by gobbs your right!