Advanced/Technical diving and mechanical aptitude

[netmage]

CaveDiver -- You wrote and then answered V's question with the difference in use. However, I'm still curious as to whether there is any difference in the "o-rings" like you said. Do you use different material for o-rings that are used in a dynamic setting as opposed to ones that are used in a static one?

From Oxygen Compatible O-Rings, Lubricant and Tools - Dive Gear Express

"The soft O-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 O-rings are more durable in static applications where the O-ring is providing a seal with stationary or occasionally moving parts, such as a valve."

PS... adding for clarity,.... Material selection when relating to scuba applications has no bearing on static vs. dynamic use. Material selection is a factor when considering a piece of equipment suitable for exposure to O2. See above link for additional info on materials as well.

 

[Cave Diver]

CaveDiver -- You wrote and then answered V's question with the difference in use. However, I'm still curious as to whether there is any difference in the "o-rings" like you said. Do you use different material for o-rings that are used in a dynamic setting as opposed to ones that are used in a static one?

Depending on the setting they are used in, yes they can be such as in a hydraulic cylinder. I'm not 100% sure about some of the ones in SCUBA in regards to the materials. I'd normally try to verify it's composition/hardness before replacing.

My reason for mentioning that was that a little different care would be taken installing an o-ring on a dynamic seal. Because it's subjected to movement after installation and may not be visible to inspection, greater care is required to make sure it seats properly.

Also, depending on the material the o-ring is made of it may be more susceptible to damage or mishandling.

 

[redacted]

CaveDiver -- You wrote and then answered V's question with the difference in use. However, I'm still curious as to whether there is any difference in the "o-rings" like you said. Do you use different material for o-rings that are used in a dynamic setting as opposed to ones that are used in a static one?

In some cases, I do. The preferred material for years seems to have been Nitrile (Buna N) and it generally has very suitable characteristics for scuba applications with one exception; resistance to ozone and oxygen. So, it looks like most of the industry has switched to EPDM and Viton (it does seem to be a trade secret) which are as good or better than Nitrile in all desirable scuba characteristics except cost. But one area where these materials are not rated "the best" is dynamic characteristics which includes resistance to extrusion. Extrusion refers to the tendency for an o-ring to flow when exposed to high pressure differentials. A better material for extrusion resistance is Polyurethane. The only application I use this in is the HP piston o-ring on my older Scubapro balanced piston 1sts (Mk5/7/10). Some folks may also use them tank yoke valves. The newer Scubapro BP 1sts (Mk20/25) have a very different design solution for this seal and don't seem to have the extrusion problem of the older design. Surprisingly, Polyurethane is rated poorly for water resistance, yet it works OK in scuba since most of our time is spent in a surface interval.

BTW, I also have no problem using nitrile in some applications. For example, I have Nitrile -014 tank yoke o-rings readily accessible on most of my stages. So, when that dive op provided tank won't seal, it takes just a minute to fix.

 

[AfterDark]

Have you estimated what you have spent to service your MkV all these years?

No, but I'm sure I've bought it a few dozen times already, when you consider reg service is almost what it cost to buy it originally. However it's like an old friend that has never let down. It's the only reg I've ever dived with stance one other time.
To buy a top of the line Scubapro reg today (which was what a MKV was when I bought) would set me back over $1000.00. I'm happy with what I have why change?
I'll add that it has been retro fitted with every improvement that Scubapro made to the MKV down through the years, so it's also a cold weather reg with the environmental mod. I'm considering having it placed in my coffin when the time comes.

 

[redacted]

No, but I'm sure I've bought it a few dozen times already, when you consider reg service is almost what it cost to buy it originally. However it's like an old friend that has never let down. It's the only reg I've ever dived with stance one other time.
To buy a top of the line Scubapro reg today (which was what a MKV was when I bought) would set me back over $1000.00. I'm happy with what I have why change?
I'll add that it has been retro fitted with every improvement that Scubapro made to the MKV down through the years, so it's also a cold weather reg with the environmental mod. I'm considering having it placed in my coffin when the time comes.

I do understand that. I dive mostly Mk5s and Mk7s which I have bought on e-bay in the last 10 years for about $25 per stage. I service them myself so the initial service may run me $10 - $15 worth of parts and then under $5 per year in parts to keep them in top shape.

 

[northen diver]

Depending on the setting they are used in, yes they can be such as in a hydraulic cylinder. I'm not 100% sure about some of the ones in SCUBA in regards to the materials. I'd normally try to verify it's composition/hardness before replacing.

My reason for mentioning that was that a little different care would be taken installing an o-ring on a dynamic seal. Because it's subjected to movement after installation and may not be visible to inspection, greater care is required to make sure it seats properly.

Also, depending on the material the o-ring is made of it may be more susceptible to damage or mishandling.

I prefer to use the factory orings. This way there is not a question of the oring being of the improper materail, size or thickness. For the Conshelfs and Sherwoods, the kits only cost me around 7 dollars. Both of these manufactuers has the complete rebuild procedures with part numbers on the internet. If you want the special tools there are a few companies that sells the tools to anyone. I just started to purchase these tools a couple years ago to speed up rebuilding my 5 regs, but had rebuilt my regs for many years without them. With an $25.00 IP gauge and a $50.00 manometer, it really isnt that difficult.

 

[halocline]

The bit about 'certified' technicians is really kind of silly. The 'certification' is a one or two day no-fail seminar for which the only qualification is that attendees work for a dive shop.

Regulators are pretty simple devices; MUCH simpler than working on cars, for example. I never fails to amaze me that someone would do their own brake job but not touch their own regulators. The dive gear industry has done a good job of brainwashing the general rec diving population.

One real advantage, IMO, of tech divers (and divers in general) working on their gear would be a breaking down of the persistent myths, lies, and half-truths that permeate the marketing of dive gear.

Personally, I find it very enjoyable to work on my own gear, to me it adds a level of involvement with diving, undoubtedly will save me quite a bit of money in the long run, and removes any anxiety I might have about someone who is obviously not qualified ruining my gear. As far as resources go, the Harlow book is an excellent one, and it's very helpful to have a mentor. I was very fortunate that Awap agreed to work with me on rebuilding regs, and I'd be happy to pass on the knowledge to anyone in my area who wants to learn. I'm sure there are many people who would likewise help other divers in their area.

Getting back to the static vs dynamic o-rings, in general there are no differences in the o-rings themselves (in scuba application) but the replacement schedule is often different. Scubapro annual rebuild kits include all o-rings that are in dynamic applications but not static ones. As Awap points out, there are different materials for o-rings that have somewhat different characteristics, and some of those are ideal in specific applications. One specialized application is with o-rings that have a severe pressure differential, like HP piston stem o-rings, 1st stage balance chamber o-rings, HP spool (SPG) o-rings, and tank o-rings. Higher durometer (stiffer, basically) o-rings seem to hold up better in those situations, although the HP spool and balance chamber o-rings are so small that extrusion seems to be less of an issue. I'm not sure why that is; certainly the total pressure is less, but there's less material as well. It could be that the profile of the o-ring is different; IOW the smaller o-rings might be much "thicker" than the larger ones in proportion to their overall size.

 

[northen diver]

The bit about 'certified' technicians is really kind of silly. The 'certification' is a one or two day no-fail seminar for which the only qualification is that attendees work for a dive shop.

Regulators are pretty simple devices; MUCH simpler than working on cars, for example. I never fails to amaze me that someone would do their own brake job but not touch their own regulators. The dive gear industry has done a good job of brainwashing the general rec diving population.



Yeah, but when your freshly rebuilt reg decides to free flow at 60 fsw, you die. However when your freshly rebuilt brakes fail on your car doing 60 MPH down the highway, you have the seat belt and air bag to protect you from death. You only seriously hurt or kill the other person that you hit. Besides, Chilton is so hard to read.

 

[ScubaSteve]

Yeah, but when your freshly rebuilt reg decides to free flow at 60 fsw, you die.

:w-t-f: It is not like the diver is wearing split fins, a poodle jacket and multiple spare airs. A free flowing reg will never be the cause of a properly trained diver's death.

 

[northen diver]

:w-t-f: It is not like the diver is wearing split fins, a poodle jacket and multiple spare airs. A free flowing reg will never be the cause of a properly trained diver's death.

Nor will an airbag or seat belt always save you in an accident. And Chilton is actually quite easy to read.




sar·casm [ sr kàzzəm ]

noun Definition: cutting language: remarks that mean the opposite of what they seem to say and are intended to mock or deride