Piston or diaphragm

[mcohen1021]

I'll take piston over diaphragm. Why? 1. They are bulletproof. 2. I can service them myself. 3. I've dove them to 130' in 42°F water and had no problem when my buddy's high end diaphragm freeflowed. 4. Even when doing milfoil remediation pulling mats I never had a problem, and when I clean them there's nothing inside - I do rinse well though.

^^^ YES - exactly why I prefer piston.

 

[stuartv]

I'll take piston over diaphragm. Why? 1. They are bulletproof. 2. I can service them myself. 3. I've dove them to 130' in 42°F water and had no problem when my buddy's high end diaphragm freeflowed. 4. Even when doing milfoil remediation pulling mats I never had a problem, and when I clean them there's nothing inside - I do rinse well though.

If you can service them yourself, why couldn't you service a sealed diaphragm yourself?

Without knowing your and your buddy's SAC rates at the time of the freeflow, it's pretty hard to attribute the example you gave to 1st stage design. Do you even know for sure that the freeflow was a 1st stage issue? How do you know it wasn't his 2nd stage that iced up and caused the freeflow?

The posts from @rsingler seem pretty convincing as a case for just sticking to sealed diaphragm first stages.

I mean, it definitely seems to me that a good design of either type would really work just fine, even for deep diving under ice. But, a sealed design will hold up better, long term. And, from what I gather, a sealed piston design is more of a pain to service. I guess Atomic is the only major manufacturer making sealed piston 1st stages? And, unfortunately, I think they are too rich for my blood.

Barring putting the Mk19 back into service, it sure would be nice if ScubaPro would offer a Mk25 with an option to seal it.

 

[DA Aquamaster]

Diaphragm first stages are not an ideal choice for an O2 reg, as that diaphragm is a large chunk of fuel, and they take a little more care in valve management to prevent ignition as the results are much more spectacular if you light one up.

 

[rsingler]

If Atomics are too rich for your blood (though I would disagree with regard to the Z's), consider the Sherwood 9000 that @DA_Aquamaster mentioned. A very innovative sealed piston that performs extremely well dry at a good price. Much easier to seal than Atomic .

 

[rhwestfall]

Sealed diaphragm (SP Mk-17) for deep cold (though Poseidon MK-2/Xstreams are frequently my recent tech kit), rugged piston (SP MK-2) for shallow Deco on rich mix (though I also use a DR RG3 ICE for my 02). Prefer second stage to have a metal air barrel to minimize freeze flows. I'll use 109/156 seconds due to the massive heat sink they provide.

Wife and daughter are using diaphragm HOGs for cold (Tobermory) recreational. I'll use a DH (Kraken or PRAM) there when diving with them.

YMMV

 

[stuartv]

I have been thinking that I would really like to have all identical regs, for everything from back gas to O2, just for simplicity.

But, it seems like all you experienced folks go for something different (e.g. the Mk2) for the richest deco mix. I currently have the Hollis O2 reg for that. Maybe I will take y'all's advice and stick with having a dedicated, mission-specific (so to speak) reg for my richest deco mix and just try to settle on a common reg set for everything else.

How does a Mk2 work for intermediate deco mixes, like EAN50 at 70'? EAN32 at 130'?

I'm not yet diving with 2 deco gases, but I'm working on it....

 

[tbone1004]

@rsingler the Genesis DAD system is pretty slick for a sealed piston, though it sadly doesn't swivel.

@stuartv mk2 is fine on ean50 and fine at depth, it just really should be paired with a balanced second stage. Depth doesn't matter to unbalanced first stages, only tank pressures.
I don't personally like the MK2 design because they stick out quite a bit. I use the Piranha "balanced" version of the MK2 that I think DGX sells as well. It's a WMD design and it works quite well for $60 it's just a bit chunky. The MK5/10's are a lot more streamlined. I've recently purchased 4 for dedicated deco regs since they have the swivel turret and side profile that is much nicer IMO for all regulators.

I'm using MK20/Jetstreams for backgas due to the swivel turrets and they were cheap *I will probably switch out with some other first stages at some point, but I just did inventory and have 24 of them, so it'll have to be a screaming deal*. Poseidon 3960's/jetstreams for stages and deep deco bottles, and MK10/109's for EAN50 and O2 with that WMD reg now dedicated as a surface/emergency O2 reg, and an O2 cleaned Poseidon first stage on my Atmosphere FFM for IWR and/or any random FFM work I have to do.

There is something to be said about having one regulator for everything to keep service easy, however the issues of diaphragms with O2 have me a bit spooked, especially after Rick Allen's incident since he's a fellow NC State diver and is part of the family. It also gives me one extra step of touch validation on the regulators if in 0viz *it's like #18 on the make sure I don't tox myself list, but it's a good quick step since they are physically very different from my stage regs*, and it's worth the potential piston issues to me since they don't get used that much and can be relatively protected. They are not something I'd want to drop as stage bottles in some of the caves that I dive in though where I've seen about 90% of the entire bottle get swallowed up by the mud

 

[stuartv]

I like the Sherwood 9000 first stage. It is also a flow by piston design, but it uses a stack of Belleville washers to increase the working range at pressures over about 400 psi, so it offers good performance, while maintaining the general simplicity of flow by piston operation. Unlike the Mk 2 or Mk 10, it also has a sealed ambient chamber - in this case via a pressure pad and diaphragm on the base of the regulator that operates a Schrader valve to increase pressure in the ambient chamber. If I saw them available in significant numbers and at low prices, I'd consider them for stage use, If the IP could be more precisely adjusted, I'd modify one to a fixed IP design and use it for an O2 reg on my KISS rebreather.

I can't find the Sherwood 9000. But, in looking, I found the Sherwood SR2. The 1st stage is a dry sealed balanced piston with a swivel turret. It looks like the best of all worlds. So, what's wrong with it?

 

[rsingler]

The Sherwood 9000-series is the second to last recent innovation by that firm. The SRB 9110 was part of the last Brut combo, for example:

9000

• rsingler
• Nov 9, 2017

It utilizes a unique sealed secondary DIAPHRAGM that senses sea water pressure to push on a simple old Schrader valve (Part #18)! Opening that valve adds HP gas to the IP chamber, compensating for increasing depth. The entire assembly is dry, and as @DA_Aquamaster noted, the HP knife edge uses Bellevue washers to respond to decreasing tank pressure. All VERY elegant. IMO, Sherwood's recent work has been singularly underrated. But out here on the Left Coast, we rarely see that brand. I bought one to tinker with, though. Very, very nice, and the Brut second stage is bullet proof.

Your example, the SR2, is a reprise of a different concept for dry piston sealing which is similar to the old Beauchat V4. Beauchat used three metal rods linked to a screw-in plate to adjust piston IP on the fly, just like the hex-fitting on a diaphragm. Sherwood, on the other hand, uses similar rods that sit underneath another secondary sealed DIAPHRAGM to augment the spring force on the back of the piston to respond to increasing depth (part #6):

SR1

• rsingler
• Nov 9, 2017

As Sherwood put it in their service seminar, these first stages are "diaphragm-piston" designs. Cute, but appropriate.

In the case of the SR1, a design flaw in tuning the second stage led to the SR2, but the basic concept is the same. The advantage of the SR1/2 is that the bore of the piston is HUGE, and the flow of this regulator is unsurpassed by anything from Atomic or Scubapro. The problem is that the legs that push against the back of the piston are part of a plastic molding that will not survive mistreatment. While it avoids the corrosion/binding problem that the Beauchat had, it won't survive any mistreatment by a tech. I don't know if they've moved from plastic to metal on those pushrods when the SR1 went to SR2. My Sherwood certification is not current.

Two good designs, but I'd defer to DA Aquamaster on usefulness for tech.

Lol, we've sure strayed from the OP's post regarding piston vs. diaphragm with this tec thread. Hijack!

 

[_Ralph]

I have been thinking that I would really like to have all identical regs, for everything from back gas to O2, just for simplicity.....

This is what I do. Every reg is the same. Backmount, sidemount, RB, Argon, Stage/Deco.

Fewer kinds of service kits to stock, and if needed, just grab another reg .... (similar thing with valves ... although I haven't been as successful in that department)

_R