New regs

[do it easy]

Well couple years ago everyone bailed on Apeks due to the IP creep issues and some runaway ascents + DCS hits therefrom. Guess those have been forgotten and the latest fatality (icing free-flow) in Canada has pushed people back towards sealed diaphrams.

Actually I doubt those "contributing" here know much about either of these events. They are just spouting off. :light:

That's a good point- if I recall, the issue was that the second stage was detuned and it masked the IP creep of the first stage.

 

[rjack321]

That's a good point- if I recall, the issue was that the second stage was detuned and it masked the IP creep of the first stage.

As I recall it was an atx200 and he would detune the 2nd stage with the knob when he stowed the reg for deco. The IP was way up and without breathing on the 2nd stage, the LP hose to the inflator turned into the path of least resistance. The runaway inflator shot him to the surface, missing most of his stops. Was in Monterey/So. Cal. somewhere.

I had one of these failure simulated in class and they are really hard to recover from. Definately scary.

Piston = no IP creep issues over time but increased risk of 1st stage free flow due to freezing of unsealed 1st

Diaphram = Slightly lower risk of freezing 1st stage, increased risk of IP creep leading to 2nd stage (or inflator) free flow.

Gotta choose your poison.

 

[do it easy]

Gotta choose your poison.

For cold water, I'll choose the diaphragm! I can manage the IP creep by checking with a guage. The 1st stage freeze up doesn't give as much warning, although there are ways to prevent it (not overworking the reg).

I knew there was a reason that I liked 2nd stages without adjustments. Of course, an IP guage will let you have the best of both worlds.

 

[fweber]

As I recall it was an atx200 and he would detune the 2nd stage with the knob when he stowed the reg for deco. The IP was way up and without breathing on the 2nd stage, the LP hose to the inflator turned into the path of least resistance. The runaway inflator shot him to the surface, missing most of his stops. Was in Monterey/So. Cal. somewhere.

I had one of these failure simulated in class and they are really hard to recover from. Definately scary.

Piston = no IP creep issues over time but increased risk of 1st stage free flow due to freezing of unsealed 1st

Diaphram = Slightly lower risk of freezing 1st stage, increased risk of IP creep leading to 2nd stage (or inflator) free flow.

Gotta choose your poison.

Is the assertion that piston regs won't suffer IP creep: A simple observation of what problems are being reported, or, is there some design aspect that would prevent a piston reg from suffering IP creep?

Agrred though, that I think this may be a case of some guys getting in some early season dives=cold water, perhaps high flow rates and venting(pun alert) about the fact their expensive SP pistons froze. While I dive Apeks' I can't see any reason not to use SP. Other than perhaps ice or extremely cold diving. Neither of which are probably of much concern to the OP.

 

[Tim Greaves]

:lol:
That was very....um...informative. Would you care to explain how you're a "master diver" with <25 dives?

He just doesnt have his login setup correctly yet.. He has over 300 dives and yes, he is very much a master diver..

 

[rjack321]

Is the assertion that piston regs won't suffer IP creep: A simple observation of what problems are being reported, or, is there some design aspect that would prevent a piston reg from suffering IP creep?

Pistons can sometimes have a little (<5psi) IP rise over the first dive or two with a new piston. Generally they don't at all and IP is fixed. The design essentially prevents them from having a catastrophic IP rise like diaphrams can have. Oxyhackers reg book has exploded diagrams which are very helpful.

1st stage freezeups are comparatively rare even with unsealed pistons. I suspect some of those reported some here are hoovering their regs while mashing the inflator.

2nd stage or LP hose free-flows due to a massive IP rise are also relatively rare. But sealed diaphram regs should not be forgotten about just because they are sealed. In fact they require as much or more diligent maintenance.

Pistons will virtually always beat a diaphram in gas delivery, not that its ever a physiological limitation of a diaphram reg.

 

[fweber]

Pistons can sometimes have a little (<5psi) IP rise over the first dive or two with a new piston. Generally they don't at all and IP is fixed. The design essentially prevents them from having a catastrophic IP rise like diaphrams can have. Oxyhackers reg book has exploded diagrams which are very helpful..

O.K. Generally, DS4 and DST's don't have any creep either. I have Harlow's reg book at home but not here in front of me at work. How does the design of piston firsts "prevent them from having a catastropic IP rise like diaphrams can"?

I understand if you don't have time to go over this right now. I'll make sure to take a look this evening.

 

[rjack321]

I mispoke a bit. Pistons are not necessarily immune by design from IP blowouts. They just don't happen in the real world though.

The only way (I can think of) the IP can change on a mk20 is:
the crown gets a gouge and the gas leaks past the seat
the HP seat is not fitting the crown
the shims go kapooy

None of these can really happen UW/in use. The HP seats don't seem to wear out or get clogged and leak at that point, even in old tired regs. Pistons are a more "bulletproof" design in this regard. Crud is able to cause more problems at the HP seat in diaphram regs.

Here's a good thread reinterating these issues:
http://thedecostop.com/forums/showthread.php?t=14166

 

[rjack321]

O.K. Generally, DS4 and DST's don't have any creep either.

Not sure I agree on that point. I know some folks with sub-optimal service schedules who have had creep/flow issues. Not catastrophic, just annoyance at discovering the reg wasn't going to work today.

The original SP Mk2 unbalanced piston can probably go a decade or even 2 without service or even rinsing and still perform flawlessly as designed - now that's reliable!

 

[Tim Greaves]

PS i have 4 dry suits ;-)

Correction... 3 drysuits.. You know youll be drunk one night and hand the Viking over..