Regulator Roundtable Q&A

[Jim Lapenta]

Yeah, you might be breathing off of it and do you really want to hand an already stressed diver a reg that breathes like crap? Or do you want to be handed one? I don't.

 

[halocline]

There are lots of full size unbalanced downstream 2nd stages that breathe about as well balanced 2nds. The old 109 is barely distinguishable from the balanced/adjustable, for example. The problem IMO is with the compact or reversible alternates.

I always thought that the idea behind the unbalanced alternate in the old tech circles was to alert the diver if there was a problem with the first stage HP seat, because an unbalanced 2nd stage will free flow more readily with IP creep. I can't remember where I heard that or if it's even true.

 

[Couv]

T... because an unbalanced 2nd stage will free flow more readily with IP creep. I can't remember where I heard that or if it's even true.

While I have not tested this idea, it makes sense. The closing force of an unbalanced spring will remain the same as it opposes the increasing IP; whereas the closing force increases along with the IP due to the pneumatic spring found in a balanced poppet design.

Conversely, as the IP decreases due to lower tank pressure, the closing force will also decrease with a pneumatically balanced poppet. Some divers consider this a feature in that a pneumatically balanced second stage has relatively even breathing characteristics over a range of IP. Others divers prefer the the "early warning" of increased breathing resistance as tank pressure (and IP) drop.

Halo know this already. Just a post for the benefit of those who have not read the Gospel according to Harlow and Wolfinger.

 

[PfcAJ]

I don't really know either, except for the things that Jim mentioned; DIN first stage, hose lengths for specific configurations. There is an old tradition of cave divers preferring 2nd stages that have removable covers under water in case they get filled with silt or some other contaminant, although I have never once heard of a diver who actually had to take a 2nd stage apart and fix it in a cave.

ive had to do it and seen it have to be done on a few occasions. It's a thing.

 

[ams511]

Yeah, you might be breathing off of it and do you really want to hand an already stressed diver a reg that breathes like crap? Or do you want to be handed one? I don't.

I don't understand your answer. The performance (balanced) primary would be handed off to the stressed diver while the unstressed diver would be using the unbalanced secondary (back-up) regulator. Also unbalanced designs are not necessarily bad, even "classic downstream" designs like the US Divers Conshelf, Sherwood Magnum, Scubapro R190, Mares MR-12 breath pretty well when properly tuned.

 

[Jim Lapenta]

When properly tuned. Agreed. I have had some students show up with crap octo's they got talked into by someone and they breathed hard enough to make me think there was something seriously wrong with them and gave me some anxiety. Was also there when a student with another instructor was practicing on the surface. He handed off the octo on his rental reg and it fell apart.

 

[Fishpie]

I think the change from balanced primary and downstream backup to both 2nd stages balanced came about when some well known tech divers changed over from Scubapro to Apeks.
Don't really want to dig up the old "overbalanced" 1st stage nonsense but this might well have been the reason behind the change.

 

[ams511]

When properly tuned. Agreed. I have had some students show up with crap octo's they got talked into by someone and they breathed hard enough to make me think there was something seriously wrong with them and gave me some anxiety. Was also there when a student with another instructor was practicing on the surface. He handed off the octo on his rental reg and it fell apart.

I know what you mean. A buddy of mine uses one of the AL puck style octo and it breathed very hard. He thought that is the way an octo is supposed to breath. When I asked him to try mine, an Apeks TX-50, he was like wow it breathes as good as my primary (He has a Titan LX).

I had a cheap Prosub octo on my backup set for a long time. It was a regular size octo and it worked fine.

 

[Pinecube]

I've got a question: I've heard that regs with a metal barrel are better in cold water, but then I've also heard that regs with a plastic barrel are better in cold water. What are the differences between a metal barrel and plastic barrel regulator when in cold water?

 

[ams511]

I've got a question: I've heard that regs with a metal barrel are better in cold water, but then I've also heard that regs with a plastic barrel are better in cold water. What are the differences between a metal barrel and plastic barrel regulator when in cold water?

Metal is a better conductor of heat than plastic. Unless you are diving in sub-freezing water the heat from the water (and your breath) will help keep ice from forming inside the regulator. I have never heard anyone say a plastic barrel is better.