Type of O-rings to be used on 1st Stage

[dhillman]

Thank you Luis. I will try to get in touch with this dive shop. I have some friends there in Mayaguez. Do you think he will remember you? If you happen to remember the name of the store please let me know. It would be ideal if I can get that dealer to sell me some of these kits and parts for the regulator. Anyway I'll let you know. I am preparing myself to go to Vieques Island this weekend to have some Spearfishing and U/W Photography. I will also test a used Mk20 1st stage coupled with a D-400.

Will keep in touch,
Hasta luego.

Darrel

 

[Luis H]

The name of the shop is "The Dive Shop"
Here is the web site:
The Dive Shop Puerto Rico


I actually talked to Jaime Braulio Jr. about a year ago on the phone and I email him some copies of 30 yr. old brochures of their store with pictures of him from back then, but I actually didn't know him. I think it was Miguel (Pili) Pagan who used to run the store back in the 70's, but he is retired.


When I was visiting last November I tried to visit their shop, but no one was there. I left some papers for Jaime, but don't know if he ever got them.

Have fun in Vieques.

Buena suerte

 

[Couv]

Personally I would avoid viton o-rings unless you're planning on high percentage O2 use. Viton is supposedly not as good as EDPM, nitrile, or polyurethane for extrusion. I would just use the BN70 series from oringsusa.com for most applications. I see that they have changed their policy on quantity for the polyurethane duro 90s, they used to sell those individually. Oh well, it was good while it lasted. If I were ordering right now, I'd probably just get the nitrile duro 90 for the HP piston, maybe also for the HP seat seal, and duro 70 for everything else. Color does not matter.

Awap likes the EDPM, and I've heard that's what SP uses in their kits, but comparing those to the nitrile ones I've bought from oringsusa I can't tell any difference. Couv is pretty knowledgeable about various o-rings so maybe he'll chime in.

My fellow suspects,

(for the short version, skip to the bottom)

We went through a similar debate on selecting o-rings a few times before, but it is always good to see fresh ideas, points of view, and anecdotes.


I did a little homework after taking apart a few regulators with all sorts/unknown types of o-rings, some looked like miniature toasted bagels and crumbled upon removal. Conversely, some had no apparent problems at all so I have tried to add a bit of logic in selecting o-rings for my equipment.

An engineer I corresponded with who's job is failure analysis recommended FKM (Viton). However, his bottom line for scuba regulators was not to worry too much over it as any quality o-rings do a good job, are relatively cheap, and are easy to replace. He recommended FKM over EPDM because (in his view) the final product is more consistent in hardness and elasticity. Now, there are few post here made by people for whom I have a lot of respect (Pesky, DA, Oxyhacker) recommending against FKM, but on the other hand Global (for tank valves), Dive Rite (regulators and tank valves), Thermo (valves) and probably a few other companies in the industry use and recommend FKM even with 100% O2. I have been used FKM o-rings for a several years now and have never had one fail.

Well, where does that leave us? The o-ring materials most often mentioned here, FKM, EPDM, Polyurethane (Polyester or Polyether) will all work well. Even Silicone, Butyl Rubber, Nitrile etc will work in almost all of the applications, but lets not get too carried away because we might be here forever trying to come up with a candidate.

The three most popular materials, FKM, EPDM, Polyurethane are all safe for 100% O2 use so why not use one of these just in case high O2 ever becomes an issue.

So here we go with my selection method:
Cost: If you buy in bulk, hardly ever an issue, I like the idea of a group purchase so count me in, but if you stock too many....

Shelf life An issue I do not see mentioned often. According to O-rings, inc. http://www.oringsusa.com/html/shelf_life.html FKM and EPDM have unlimited shelf life, PU shelf life is only 5 years....so there goes PU.

Quality: Working in the aviation/aerospace industry for over 30 years has made me anal about quality. For this reason, I only buy aviation grade o-rings. Hardware store o-rings will probably work just fine, but it is nice to know there has been some quality control and sample testing in the manufacturing process.

Hardness: As pointed out before, Shore A 70 or higher duro for most application, 90 for high pressure differentials, like piston stems and tank valves. In a post long ago and far away, I mentioned only buying duro 90 for the -010 o-rings, but I have had problems in one application. The second stage orifice gets difficult to install with a high duro o-ring, so I try to use something a bit softer there. (do any of you have any 70/75 to swap?)

Material: According to the engineer mentioned above, FKM is more consistent than EPDM and less subject to compression set, but I would not have any problem using either. Both have a wide temperature range. EPDM -40deg F to 25deg F having the edge over Viton's -10deg F to 400 deg F, but I usually avoid diving in those conditions if I can.

So there you have it- to keep things simple, I use FKM duro 90 for pretty much everything except my orifice. ;-0 YMMV

couv

A few helpful links:
http://www.oringsusa.com/html/scuba.html
http://www.parker.com/literature/ORD%205700%20Parker_O-Ring_Handbook.pdf
http://www.marcorubber.com/material_chart.htm

 

[redacted]

When I started out, I studied a Parker O-ring catalog and selected viton due to its 15+ year shelf life vs EPDM at 50 to 10 years (and nitrile at less than 5 years). Those little bags of o-ring that I used up in the first 5 years I replaced with EPDM. I really have not had any problem with any o-rings including some in nitrile that I used when I ran out of more desirable materials. I still buy the occasional old scubapro reg with a rainbow of o-rings probably pushing 15 years old that still works fine when I slap it on a tank for that first test. Except for a few temperamental applications, it just does not seem to matter much. And if one does fail, it is almost always rather graceful - a slow leak. Finish the dive and either replace the o-ring from your save-a-dive kit if it is an easy one, or go to a backup regulator and keep diving. You do have a complete backup reg in your save-a-dive kit, right?

Couv - Your problem with the orifice o-ring may be due to size, not material. I have found that the 2-010 o-ring on a scubaro metal orifice to be a little tight. That size is not aproblem on the plastic orifice but, sometimes, would not work with the metal ones. I went to the 3-902 which is the same ID but just a tad thinner material and it works fine on all SP metal orifices. Notice that the scubapro schematic show different o-ring part numbers on the metal vs the plastic orifice.

I'll go ahead an order a batch (100) of the PU 2-010, duro 90 and repack in quantities of 5 or 10 for whoever wants them.

 

[Couv]

When I started out, I studied a Parker O-ring catalog and selected viton due to its 15+ year shelf life vs EPDM at 50 to 10 years (and nitrile at less than 5 years). Those little bags of o-ring that I used up in the first 5 years I replaced with EPDM. I really have not had any problem with any o-rings including some in nitrile that I used when I ran out of more desirable materials. I still buy the occasional old scubapro reg with a rainbow of o-rings probably pushing 15 years old that still works fine when I slap it on a tank for that first test. Except for a few temperamental applications, it just does not seem to matter much. And if one does fail, it is almost always rather graceful - a slow leak. Finish the dive and either replace the o-ring from your save-a-dive kit if it is an easy one, or go to a backup regulator and keep diving. You do have a complete backup reg in your save-a-dive kit, right?

Couv - Your problem with the orifice o-ring may be due to size, not material. I have found that the 2-010 o-ring on a scubaro metal orifice to be a little tight. That size is not aproblem on the plastic orifice but, sometimes, would not work with the metal ones. I went to the 2-902 which is the same ID but just a tad thinner material and it works fine on all SP metal orifices. Notice that the scubapro schematic show different o-ring part numbers on the metal vs the plastic orifice.

I'll go ahead an order a batch (100) of the PU 2-010, duro 90 and repack in quantities of 5 or 10 for whoever wants them.

Awap,

Actually, I was aware that orifice did not take -010, but in trying to keep my o-ring stock to a minimum, I always replaced the orifice o-ring with a -010
I did not know the actual size, though, thanks.

Same issue with the balanced poppet...-002 works fine, but probably should be a different spec.

I have the same experience as you with failed o-rings. Even the o-rings I removed from garage kept, over-heated POS o-rings crumble to pieces when you take them out, but somehow still managed to do the job when installed.

c

edit: Awap....I usually order o-rings by the NAS16xx number or M83248 number, so would the full number of that o-ring be NAS1602-902 or is that an asa number?

Thanks

 

[pescador775]

Thanks, coov, for your due diligence. I will consider your remarks carefully. I have been testing Viton and the harder compound may not be as bad as the tables of mechanical properties indicate.

About shelf life; I have lived longer than most of you so feel qualified to respond. Nitrile O rings will last on the shelf almost forever, at least 20 years. However, from time to time, something odd happens. Out of a utility box of O rings, I found that all but one size of the rings were in good shape after two decades. I believe this was the 013 (which is probably irrelevant), these had turned hard as a brick. Very strange as the remainder were still like new. The nitrile O rings in a compressor filter (dynamic fit) started to leak in cold weather after 25 years of service. Urethane has a long life. After a couple years, the urethane ring will turn yellow but nothing further. I have left urethane rings in place on tank valve faces for 10 years. They continued to seal perfectly during all that time. Manufacturers are leery of the color change as it might affect the sale value of the product. Now, my urethane O rings were purchased from dive shops about 20 years ago and I still have a few. I don't know if they are milled, cast, polyester or what. I notice that paintballers can purchase packages of the cast type but SCUBA related sizes are catch/catch can.

 

[redacted]

Awap,

Actually, I was aware that orifice did not take -010, but in trying to keep my o-ring stock to a minimum, I always replaced the orifice o-ring with a -010
I did not know the actual size, though, thanks.

Same issue with the balanced poppet...-002 works fine, but probably should be a different spec.

I have the same experience as you with failed o-rings. Even the o-rings I removed from garage kept, over-heated POS o-rings crumble to pieces when you take them out, but somehow still managed to do the job when installed.

c

edit: Awap....I usually order o-rings by the NAS16xx number or M83248 number, so would the full number of that o-ring be NAS1602-902 or is that an asa number?

Thanks

I'm sending you a couple samples (AS568-902, EPDM, duro 70) but this looks like the right one in the mil spec(MS) series duro 70: oringsUSA or this in duro 90: oringsUSA.

 

[halocline]

I really seem to remember reading in a few places that viton does not have the abrasion resistance that EPDM, polyurethane, or nitrile has, and that it's only advantage in scuba use was O2 compatibility. I could certainly be wrong.

Of course very little of this matters in a practical sense except for the HP piston o-ring, maybe the HP seat seal, and maybe to a little extent the LP piston o-ring. We've seen 20+ year old regs with the original o-rings still doing the job fine. It is kind of interesting, though.

 

[redacted]

I really seem to remember reading in a few places that viton does not have the abrasion resistance that EPDM, polyurethane, or nitrile has, and that it's only advantage in scuba use was O2 compatibility. I could certainly be wrong.

Of course very little of this matters in a practical sense except for the HP piston o-ring, maybe the HP seat seal, and maybe to a little extent the LP piston o-ring. We've seen 20+ year old regs with the original o-rings still doing the job fine. It is kind of interesting, though.

According to the Parker Handbook, PU has excellent abrasion resistance; EPDM is good to excellent; and Viton and Nitrile are good. PU also has excellent dynamic qualities which includes extrusion resistance while the other 4 are good to excellent. PU, EPDM, and Viton all have excellent ozone resistance while Nitrile is poor.

 

[oxyhacker]

I would caution against puttng too much faith in the very abbreviated tables found in the O-ring catalogs. It's fun to play engineer, but there are factors, and combinations of factors, that effect performance but that they cannot cover.

For example, one parameter that it hard to quantify (I'm not even sure what the proper name for it is!) and often gets overlooked or lumped into the general category of "mechanical properties" which is how readily and smoothly an 0-ring can overcome stiction and move. This, in key dynamic O-rings like the piston O-rings on a piston 1st will be one of the key variables in how the stage will perform. That's why my general rule is not to try to outguess the factory engineers unless there is a very good reason to (O-rings failing or bursting into flames, for example), but rather use what they do whenever possible.

Also don't assume that just because Parker says a Parker Superthane O-ring has a particular attribute that Joe's Inet Bargain O-rings superthane ones will also have the same attribute to the same degree. Quality can very incredibly these days, with O-rings being made all over the world.

According to the Parker Handbook, PU has excellent abrasion resistance; EPDM is good to excellent; and Viton and Nitrile are good. PU also has excellent dynamic qualities which includes extrusion resistance while the other 4 are good to excellent. PU, EPDM, and Viton all have excellent ozone resistance while Nitrile is poor.