Best Reg for Cave diving

[Mobulai]

Although, I appreciate MK10+ regs because I can service them in the field w/o having to have a special bullet to insert the piston.

the + also has the upside of the same seat as the 20/25 so way down the line seat availability wouldn’t be a worry, I already started stacking a few 10+ conversion kits and seats for when the pistons on mine eventually get to short to live reliably.

Mk10/g250s are goated

 

[mr_v]

I was talking to a buddy about the advent of the polymer second stages and how many divers back in the day shunned them because ....plastic.

Someone at the shop took a salvaged plastic second stage and put it under the wheel of his truck and drove over it. No harm done. A metal second stage crumpled. They use the two second stages as a sales tool for a long time.

Secondhand info and it defies my expectations but that's the story.

I've heard the same hypothesis - SP109s are forever. Yeah, not really. You can crush the metal and the finish has been rubbing off from all but the most exceptional specimen. Also, 109s are a bit to big for necklaced regs.

 

[Nemrod]

I don’t know about the particulars of the 2nd stages that your dive shop used, but I know that the old SP metal case 2nds that I use hold up better than the plastic 2nd stages (mostly G250 and D300) that I own. I don’t really know or care about driving over a regulator with a truck, but let’s say that I’m extremely skeptical that any 2nd stage would survive being driven over on pavement. What I do know is that if a scuba tank rolls on my 2nd stage (it happens) then I don’t have any problems. But, as I said, pretty much every other cave diver i know uses plastic 2nd stages and somehow they’re not getting crushed either!

There is another reason I like the old metal case, too. I find that the old 2nd metal 2nd stages do not contribute as much to dry mouth. There’s a little condensation as your warm exhaled breath hits the colder metal. (Metal conducts heat better than plastic) It’s not enough to cause any problems with water in the 2nd stage, but I notice a difference over the course of a 2-3 hr cave dive.

It’s all a matter of personal preference.

I am going with the G250/G260 housings being more rugged than the brass and chrome 109. The 30% glass fiber reinforcement of the polyamide composite Scubapro second stages makes them tougher and more flexible than the typical abs plastic everyone else uses.

 

[Nemrod]

I've heard the same hypothesis - SP109s are forever. Yeah, not really. You can crush the metal and the finish has been rubbing off from all but the most exceptional specimen. Also, 109s are a bit to big for necklaced regs.

I have had no problems necklacing the 109/156 or G260 regulators. I do notice the weight of the 109 is greater in the water than the G250. The peeling chrome is annoying, too bad they did make the 109/156 seconds from stainless.

Twice now I have had a tank hit a G250 hard enough to pop the cover off and yet there was no damage. A 109 would have probably been damaged. Not going to drop a tank on one to find out .

 

[Tanks A Lot]

[...]
Twice now I have had a tank hit a G250 hard enough to pop the cover off and yet there was no damage. [...}

This happened exactly as the material was engineered.

ScubaPro uses a high-impact amorphous nylon, which is a polyamide, as you correctly point out. Amorphous meaning that the polymer chains are not arranged in an orderly fashion. Most nylons are semi-crystalline, meaning they have regions where the monomers are arranged in a crystalline structure and regions where they are randomly entangled.

The crystalline areas provide strength and stiffness, while the amorphous regions provide toughness. Since ScubaPro uses an entirely amorphous polymer, they compensate for the reduced strength and stiffness from the lack of crystalline regions by introducing fibreglass into the polymer.
The result is something that is tough and strong at the same time, the holy grail so to speak.

I always imagine their polymer as a bit like a bowl of cooled down spaghetti: All entangled in itself and therefore super tough. Strike it all you want, it's hard to break it. Unfortunately the bowl of spaghetti isn't all that strong, so that's where my analogy ends...

The South African ScubaPro representative once told me a similar story:
He wanted to supply the Navy with regulators, but the military allegedly refused on the grounds that they were “just plastic.” So he drove over one with a truck, and it still worked. He got the contract afterwards. How much of that story is true and how much he made up, I don’t know. What I do know is that you can drive over one with a passenger car, and it will work just fine.

ScubaPro is leaps and bounds ahead when it comes to polymer usage. What others like Apeks or Aqualung use doesn’t play in the same league. It's rather straightforward to break one of their second stages. Dropping a cylinder on one would certainly do it.

 

[halocline]

I've heard the same hypothesis - SP109s are forever. Yeah, not really… Also, 109s are a bit too big for necklaced regs.

Well, mine are 50 years old, it’s not forever I guess. It’s ridiculous to say that they are too big for necklaced regulators. Some people might find them a little heavier in the water, but it doesn’t bother me.

 

[halocline]

the + also has the upside of the same seat as the 20/25 so way down the line seat availability wouldn’t be a worry, I already started stacking a few 10+ conversion kits and seats for when the pistons on mine eventually get to short to live reliably.

Using the MK25 seat is not really a plus, in fact it’s a minus. Those seats are FAR more expensive than MK5/10 seats, which are available aftermarket or through SP.

My experience with the MK10+ is that it just does not lock up well. They are way more prone to creep than either the MK10 or the MK25.

 

[nickbutcher]

Does cave diving require any different attributes from regulators than any other form of diving? If I'm underwater, breathing via a regulator, it needs to reliably provide me with life-sustaining gas.

I exclusively use Scubapro regs. I have Mk25 piston first stages and S600/A700 second stages on my bailouts and Mk11 diaphragm 1st stages on my rebreather (the only modification I've made on my JJ)

I trust Scubapro. The build quality is excellent, they are very easy to service and the service kits are widely available anywhere I might be diving.

 

[Mobulai]

Those seats are FAR more expensive than MK5/10 seats, which are available aftermarket or through SP.

My luck was the opposite, I could only find aftermarket ones that were double the OEM 25 seats; and the conical aftermarket ones have a bad rep for their surface finish
I still have an ok stash of conical seats in service kits, but that will get me so far — I’d love to have your source

My experience with the MK10+ is that it just does not lock up well. They are way more prone to creep than either the MK10 or the MK25.

true true, I think when I started buying mk10s I read that (by you and others on the board); I’ll only turn a 10 to a plus at end of life, when the piston gets soo short that even the tallest seat isn’t enough for good IP spec

 

[mr_v]

Does cave diving require any different attributes from regulators than any other form of diving? If I'm underwater, breathing via a regulator, it needs to reliably provide me with life-sustaining gas.

I exclusively use Scubapro regs. I have Mk25 piston first stages and S600/A700 second stages on my bailouts and Mk11 diaphragm 1st stages on my rebreather (the only modification I've made on my JJ)

I trust Scubapro. The build quality is excellent, they are very easy to service and the service kits are widely available anywhere I might be diving.

Nothing against SP, but SP is very overpriced in the USA given the alternatives.