Jim,
thanks for your observation ..the original eBay listing showed the o-rings as N70 and I have updated the eCrater listing as of now.
That said, I think this could be a good forum for the discussion of suitability.
Can you please supply a link that defines that HP application do in fact require 90 durometer ...I haven't found one yet.
My SIL has been servicing his equipment for several years and the commercial scuba kit he purchased, only has N70 o-rings. The Scubamax 450pc set doesn't even specify it, but 70 is the most commonplace o-ring used in industry. This is dictated by the geometry of the grooves used to create the seal. I am quite familiar with the Parker Handbook sect 1-2 where they describe failure modes for "static" applications.
There are many misnomers out there and people sell all sorts of things. Like Viton for Nitrox ...Viton is for high temp applications and if you think the minor extra oxygen is going to effect NBR but not your lungs, then you are kidding yourself. Note that on the OEM Sherwood kits for 1st + 2nd stages, they only specify G007A, G010A, G011B, G022A, (where A vs B is a nit), which implies they are all same makeup or they would have diff coding.
This may or may not be relevant:
What is Rubber Hardness?
from above link:
70-durometer hardness should be used whenever possible as it offers the best combination of properties for most O-Rings applications.
looking forward to settling this subject
Stew Corman
---------- Post added January 28th, 2014 at 11:25 PM ----------
FOLLOWUP POST
OK, Since Jim brought up the subject, I have put on my mechanical engineer's hat on and researched the following factoids:
All standard N70 o-rings are tested at 5000psi ....caveat: you can design the retaining grove with dimensions that will not support 5000psi
There are three types of application that are contained in scuba apparatus:
dynamic ( parts move/slide like inside regulators)
static ( stationary like computer seal )
static compression (valve mounted on tank)
here is a link to scuba applications:
About Scuba Diving O-rings | Scuba Life
here is a quote from above:
Hardness
O-rings are normally available with a hardness rating, as measured by an ASTM type-A durometer, of 70 (the “soft” kind) or more rarely a rating of 90 (the “stiff” kind). The a-rings sold on this page are 90-duro (except for the -003 SPG a-ring), and well suited for the SCUBA applications we describe. The soft a-rings are appropriate for dynamic applications where the o-ring is providing a seal with a constantly moving part, such as inside regulators. The stiff a-rings are more durable in static applications where the a-ring is providing a seal
with stationary or occasionally moving parts, such as a valve.
I have seen this reference several times and it contradicts Jim's contention:
HP applications like the HP spool should use a 90 duro o ring. Something like a 70 duro is apt to fail prematurely or blow out as it is too soft for the HP application.
SO, no I would definitely not use the -003 spool with an N90 o-ring
I have found a few conversations of tank valve seals being "blown out" and the recommendation for the harder N90 o-rings, but in that case the o-ring is being squeezed tight. I do NOT include any of those sizes in my kit.
I found a kit that denotes a mix of N70 and N90, but they claim the -014 yoke is N70, but the -112 Din yolk is N90 ...doesn't make sense and soft would appear better for yolk "clamping" ..can leak and you'd hear it, but can't blow. All the ones I have seen onsite are "soft"
As I stated earlier, many name brand kits which you have probably seen only use N70 such as:
Scuba O-Ring Kit for the Prepared Diver
All the Sherwood kits are using N70 , because all of them have moving dynamic pistons/shafts.
Dive computer seals are either static or compression, but soft is better, since there is very little pressure, even at depth and they don't get screwed in very tight.
I will make the bold supposition that BC inflators are irrelevant which durometer you use.
There is also debate on which static o-rings get lube and which are installed dry ....you will hear both sides of that conversation posted.
I would like to hear from anyone who has blown out an o-ring which would contradict any of the above.
