O-Ring Groove Design

[Tuckabag]

Hi All,

Does anyone have any references I can look up/purchase with regards to design of both static and dynamic o-rings grooves for high pressure (10,000psi) gas and liquid applications?
I've used the Parker o-ring handbook successfully for other lower pressure (approx 3,600psi) designs.
I'm assuming I just need to tighten up clearances on mating parts, but would like to see some other references for this higher pressure type work, unless the standard Parker grooves/clearances are ok for these pressures.
Thanks!

 

[hydtools]

You also have to consider using harder seal materials and anti-extrusion components. Use joint designs that create metal-to-metal closure. The grooves can be per the Parker Handbook.

Ted

 

[israelkk]

I would like to add to hydtools that metal-to-metal is for face seal only to my best experience.
For piston grove seal you will need more than just harder seal and anti extrusion component. Usually such details are not available freely. These are company's (or experts) propriety knowledge.

1. The type of anti extrusion design and material is important
2. Temperature range
3. How long it has to seal and how much leak is allowed over time (If it seals a volume).
4. Housing material and coating
5. Type of gas, sealing Helium is totally different than sealing Air, Nitrogen, Argon, etc.,

 

[Tmoose]

I'd be contacting the 0-ring manufacturer's engineering department.

I think they'll ask you all of Israelkk's excellent questions, and a bunch more.

 

[Tuckabag]

Thanks for the feedback.
We intend to use 90duro o-rings in an AED compound. Will also be using PTFE or possibly PEEK backup rings.

Will discuss with o-ring vendors hopefully they will have a HP design guide they can share.
If not we will use std Parker groove dims and err on the tighter end of tolerances to give less room for extrusion.

Always open to more feedback!
Thanks.

 

[MechyMarco]

Tuckabag,
I routinely spec out o ring grooves for static and dynamic applications. Also use piston seals (polypaks). What exactly is your application? Static or dynamic? Face or radial/axial? Loaded on both sides of seal or just one? Internal pressure? Acidic? Gas or liquid? For a start I would say to just tighten up the tolerances as per parker and give them a call to have them look over your design. They want to help.

Also, have you considered a metal to metal seal? It may be your best bet. See Parkers Metal to Metal Seal Design Guide for the rundown. You should have no prob sealing past 10k in either a face or axial application.

 

[Tuckabag]

I have both dynamic and static applications for this job.
Basically I have a cylinder with end caps that seal on the ID of the cylinder tube via o-rings. These seals have atmospheric one side, up to 10,000psi the other.
There is also a dynamic piston. I would be looking to use crown seals in lieu of o-rings on this item, however the groove dimensions are the same. This can have up to max dP of 10,000psi, or can be 0psi dP depending on the operation of the unit.
I did find a nice table that showed recommended diametrical clearances based on pressure and o-ring duro. It recommended to reduce clearance down to approx 0.05mm for 10,000psi and 90duro o-rings.

 

[MechyMarco]

Interesting you found a chart. Was it from a supplier? Only thing that I've come across is from Parker's fluid power book.

https://www.parker.com/literature/Engineered Polymer Systems/5370.pdf

See Table 2-4 on page 2-5.

All of my seal designs have been done by playing with the squeeze and extrusion gaps. Typically roll with aprox .0025'' (.05mm = .002'') radial extrusion gap and get decent seals upto around 5ksi. Liquid, internal pressure, dynamic piston seals. Mind you they are in a terrible environment and I can tolerate some leak/extrusion. How critical are leaks for your system?

 

[Tuckabag]

When I'm back in the office I'll post them. Can't remember where I found them.

Leaks are super critical in this application. Typical use is on complex hydrocarbon streams for composition analysis, so we cannot afford to lose any light ends through leak paths.

 

[israelkk]

If "Leaks are super critical in this application" then using O-rings is not the solution to my best judgment. There is also a gas permeation through the rubber seal. You should may go with all welded sealed metal bellows designed for 10000psi and the movement and forces and life cycles.

 

[MechyMarco]

If leaks are a no go up to 10ksi you're sort of forced into using a metal-metal seal. Israelkk is right about the gas permeation issue with the o ring elastomers (or piston seals). Is the piston functionality absolutely mandatory? Guessing you're using the internal piston to force the fluids out for sampling like in a syringe? Could you maybe route any fluids that blowby the piston seal into a secondary expansion vessel and then bleed them off into your sampling chamber to make sure you capture everything?

 

[ProEpro]

I would recommend a self energizing or pressure energized seal. They will have the pressure rating you need.

However, because of the contamination issues metal seals like Swagelok VCR fittings might work better for the static seals.

Someone like HIP might already have something in their catalog that will do what you need.

http://www.highpressure.com/

 

[BrianE22]

There's also Bal Seal (

http://www.balseal.com).

 

[Tuckabag]

Thanks for the feedback so far.
Metal/metal seals are not really a viable option in this application unfortunately. We need to maintain the piston function, basically we pre-load one side of the piston at or above line pressure with inert gas, then slowly allow the other side to fill from process (at line pressure) without flashing off any light ends by bleeding off the pre-charge pressure.
We have used these seals in the past on lower pressure application (up to 5,000psi) with great success. They are very resiliant and provide great sealability.

http://www.hitechseals.com/includes/pdf/Crown_seals.pdf

Have also used Bal-seals in the past, though they have not been as successful as crown seals.

We also need to disassemble for cleaning/servicing, so o-ring seals for the end caps is really ideal for this service as well. We've never had any real issues with gas permeation before, apart from some RGD issues on high pressure/temp streams with significant CO2 levels. Even then the static o-rings were not too bad, it was the dynamic piston seals and valve stem seals that copped a hiding.

VCR/bellows type seals unfortunately aren't going to work for us in this style of application.

Also @MechyMarco please see attached the chart I found online re clearance gaps.

 

[ProEpro]

You have not said what your volume is. It is probably small enough this is not an issue. However, you should double check that the increased pressure does not make it regulated pressure vessel.

Sounds like a clever design.

 

[MechyMarco]

Ahh right on Tuckabag. It's so frustrating knowing that Parker, Hitech, EPM and all the other seal manufacturers have loads of practical test data that we don't have access to. Makes sense that they don't publicly share their knowledge as that's sort of what distinguishes one from another though ya? It's funny you attached that sheet from Hitech as I was going to ask if that's what you were using. Sounds like you've got the design essentially nailed down. All you can really do is tighten up the squeeze and extrusion gap until you get an acceptable seal. Assuming friction isn't an issue of course.