DumpsterDiver emergency ascent from 180'

[halocline]

I understand. But, I often see posts around here regarding old regs that people have been using for 10 or more years without any service. Are those all piston regs then? I'm not saying I would want to, but if a good piston reg COULD reasonably go 10 years without expecting a catastrophic failure (versus a failure with slow onset) and a diaphragm regular cannot do that, then I would chalk it up as an advantage to a piston reg.

Probably the most reliable regulator design, as demonstrated by many decades of service from the USD royal aquamaster on through the decades of conshelfs and then titans, is the old USD balanced diaphragm design. Right on it's heels is the MK5 balanced piston design, and the sherwood/MK2 flow by piston design.

Each of these simple, classic regulators has literally many millions of dives without problems. I really don't think you can characterize 'diaphragm' as being more or less reliable than 'piston', nor can you successfully argue that one is more prone to sudden failure than the other.

Once you get your Harlow book and start reading up on the designs I think you'll see that each has failure points and strengths. The conshelf has 1 o-ring on the interior of the reg; ONE! The MK2 is designed so that no dynamic (moving) o-ring is subjected to HP air, another remarkably reliable design.

 

[Rusty Shackleford]

I had a MK-20 blow just before putting my rig on my back. Last Wednesday.

A back-up set of regs saved my dive.

The culprit was apparently the wrong duro O-Ring along with the backing bushing put on upside-down by the service tech. Both big no-no's.

I carry a 30cu/ft pony with a MK-2/R-190 as a back-up. My max depth (I was solo) I went to afterwards was 70ft. I could have likely breathed off the bypassing regulator if necessary but I feel the 30cu/ft would have easily allowed me a three minute safety stop at 15 feet and all of the ascent if necessary.

I made the dive with another MK-20. One the aformentioned tech never touched.

 

[soggybadger]

They do not float horizontally. And once you add a first stage and second stage and an spg (if you use one on a stage - which is a different topic).

The reasons they are popular in my opinion is:

1. The buoyancy characteristics. This is basically how much they pull us up and down in the water, especially as we breath the gas.
2. They are a convenient size. In the UK it's very very common to have ali7 (which are slightly larger) and these tend to be cheaper here. Technical divers buy there own tanks and therefore do not want a huge number of tanks to buy/service so we pick convenient ones.
3. It's small enough to be able to easily handle. It doesn't look intimidating like an ali80.

4 - and this one is going to be controversial. People get them because other people get them and they copy. Which is why in the UK it's so so popular to see an ali7 instead. It's not that we are physically different to Americans. We just do what everyone else does.

I'm going to be slightly controversial and say an ali7 is a better general stage cylinder than an ali40 (and I have both). But the reasons for that are personal to me and the dives I like to do. One of the big reasons for me is I can fill it with gas and use it for two easy boat dives deco and I like that rather than having to carry two on a boat.

I went for the ali 7 for similar reasons. Multi use and manageable.

 

[soggybadger]

Well, I for one am glad that this video was posted, as I think it is instructional, and had led to some very good discussion, about:

1. Pony bottle size (the stated reason that it was first linked in this SB thread);
2. Dive planning
3. Incident analysis
4. Diver behavior
5. Response to an emergent situation

Probably, other issues could be identified.

As several have said, we seldom have video summaries of these kind of events, and this has been enlightening. I have learned quite a bit from the discussions.

I may differ with DD and /or others on at least some specific points related to these issues. But, I appreciate the fact that 2airishuman posted the link and started this thread. Each of us will hopefully take away various thoughts, form opinions, and ideally grow as divers as a result. I don't have to agree with someone to learn from their views. And, maybe I can learn something that helps me adjust my own views.

You forgot the most important point of discussion. 6 actions on for dropped bacon.