Piston or diaphragm
- Thread starter Flycaster
- Start date
Please register or login
Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.
Benefits of registering include
- Ability to post and comment on topics and discussions.
- A Free photo gallery to share your dive photos with the world.
- You can make this box go away
- Messages
- 20,620
- Reaction score
- 15,077
- # of dives
- I'm a Fish!
as a point of clarification. The sealed boots that Atomic uses to seal their first stages are acting as "diaphragms" over each of the holes and transmitting the pressure back into the ambient chamber
So, Atomic sealed first stages use cristolube or something in the ambient chamber? And that lube separates the compressed gas from the sealing diaphragm, so the sealing diaphragm itself is not an O2 fire risk? But, for some reason, Atomic doesn't approve any of their 1st stages for use with more than 80% oxygen?
The Sherwood SR2 use a dry sealed chamber with some kind of diaphragm to seal it. Does that diaphragm pose any risk with respect to O2 compatibility?
Is there any dry sealed piston 1st stage made by anyone that is safe for O2 use?
Still wondering if the SR2 setup is any good. I appreciated @rsingler's post, but it left open whether the SR2 has any/all of the SR1's issues fixed.
And is the 2nd stage any good? I can't even find whether the 2nd stage has a metal or plastic air tube.
The Sherwood SR2 use a dry sealed chamber with some kind of diaphragm to seal it. Does that diaphragm pose any risk with respect to O2 compatibility?
Is there any dry sealed piston 1st stage made by anyone that is safe for O2 use?
Still wondering if the SR2 setup is any good. I appreciated @rsingler's post, but it left open whether the SR2 has any/all of the SR1's issues fixed.
And is the 2nd stage any good? I can't even find whether the 2nd stage has a metal or plastic air tube.
Almost, @stuartv! There are two separate issues here - O2/fire risk and keeping a reg uncorroded.
Atomic piston fire risk: Atomic has only three potential fuel sources: 1) The two orings (one around the piston shaft, the upstream half of which sees HP O2, and the Piston O-ring, which only sees IP oxygen. 2) theoretically, the knife edge of the piston, and other reg parts which see impact HP O2. They use non-fuel (?EPDM?) for their o-rings, and DON'T use Titanium for their pistons or O2 reg. Monel for the high-O2 reg. piston, for example. Titanium as a fuel source is a bit of a reach, but is flammable like Magnesium. (There are more fuel sources that are the real culprits: oils and dirt that accumulate upstream and are impacted by 100% O2 when you open a valve quickly, but I'm assuming you know that and we are both starting with O2-cleaned equipment).
Atomic anti-corrosion resistance: The use of titanium was what brought Atomic to the forefront, and everyone else copied. ZERO sea water corrosion with titanium, but as you've heard me complain, it's anti-scratch resistance is less than chrome. Therefore, for either ice protection or grit protection, filling the environmental chamber with Christolube keeps things under control, by eliminating sea water.
Now back to fire: As for 80% vs. 100% at 3000-4500 psi? That's a lawyer thing. Plenty of tec divers have been using brass/chrome regs with 100% O2 and EPDM or viton orings and Christolube or Tribolube without problems. The reason you hear the Mk2 touted is because it's so simple, and therefore has fewer o-rings that are exposed to HP O2. The Atomic M1 eliminates titanium, uses O2 compatible O-rings, and shields them from impact O2 wherever possible (e.g., the modification of their yoke bolt to put a groove for the HP o-ring land).
The Sherwood's "diaphragm" is a bit of a misnomer. Like the roof of the sealing ring on the Atomic piston, it's just a force transmitter. The diaphragm isn't exposed to O2 or air at all. It sits in the water (see diagram) and when increasing sea water pressure depresses it, pushes the stem of the Schrader valve a little until increasing IP forces the base of the piston back against it. So as with any other piston, the choice of o-rings will determine fire susceptibility. You'll have to consult with a tec guy that uses Sherwood to see if they modify it that way.
As for the second stage, the barrel is metal. A good design, and the SR1 problem was small and solved by a washer to prevent the tuning spring from catching, but not my favorite second. Very solid, though, with great WOB numbers.
View media item 204311
Again, you'd have to talk to the East Coast tec guys to see if anyone mods it for higher O2. It's only rated by Sherwood to 40%.
Last edited:
But if you end up choosing diaphragm, and want O2 compatibility right out of the box, Poseidon has the best engineering of all of them. Some folks don't care for the breathing feel of the Jetstream, but in deep water, its air delivery is unsurpassed.
And the design of the XStream first stage is the best diaphragm in the world, IMO. For IP balancing with changing tank pressure, there is a floating seat that is cup-shaped, with a seal created by a ruby ball that won't pit. The design is absolutely marvelous!
As I noted, the appropriate model is 100% O2 out of the box, and is easy to service. The XStream wasn't certified with the old Cyklon 2nd stage, but is perfectly capable of delivering the 160 psi IP needed for that downstream bulletproof second, if you don't like the feel of the Jetstream. For that subject, search some old posts - it's been discussed to death. And the old upstream valve boogie man is a non-issue.
I've attached a brochure. No, I don't sell Poseidon. I'm just a guy who services them. That will often be your determinant - finding good Poseidon service. I think the XStream is the best diaphragm first stage in the world.
And the design of the XStream first stage is the best diaphragm in the world, IMO. For IP balancing with changing tank pressure, there is a floating seat that is cup-shaped, with a seal created by a ruby ball that won't pit. The design is absolutely marvelous!
I've attached a brochure. No, I don't sell Poseidon. I'm just a guy who services them. That will often be your determinant - finding good Poseidon service. I think the XStream is the best diaphragm first stage in the world.
Last edited:
Thanks, @rsingler. I am really only interested in 1st stages with a swivel turret, so the Poseidon stuff is out.
If I could find something that would work for anything from O2 to back gas, that would be ideal. I was looking at sealed diaphragm 1sts, but this thread got me to considering whether there might be a sealed piston 1st that would work. The Atomic M1 and the Sherwood SR2 both seem like possibilities, based on specs.
But, the extra service hassle (expense) with the M1 does not (yet) seem justified (to me). And the SR2 still seems like a bit of an unknown quantity.
So, as much as "all identical regs" sounds nice, I will likely end up sticking with something like I have now - a simple, (relatively) low performance, dedicated O2 reg (or two) that, unfortunately, do not swivel. And then sealed diaphragm swivel turret regs for everything else.
If I could find something that would work for anything from O2 to back gas, that would be ideal. I was looking at sealed diaphragm 1sts, but this thread got me to considering whether there might be a sealed piston 1st that would work. The Atomic M1 and the Sherwood SR2 both seem like possibilities, based on specs.
But, the extra service hassle (expense) with the M1 does not (yet) seem justified (to me). And the SR2 still seems like a bit of an unknown quantity.
So, as much as "all identical regs" sounds nice, I will likely end up sticking with something like I have now - a simple, (relatively) low performance, dedicated O2 reg (or two) that, unfortunately, do not swivel. And then sealed diaphragm swivel turret regs for everything else.
Hi Guys:
Out of curiosity, how long does it take to cause the wear that has been shown on the body of the regulator firs stage. I have taken apart my Atomic regulators and have found some sediments on the piston and at base of the spring. Although, I don't recall seeing any wear or scratches on the "land" part of the first stage body. However, the Zirconium plating has worn away from the second stage inlet tube on my current Z2. It's rather evident, when one is brass colored and one is gold colored. I currently dive in the Monterey of California. About the only time could fathom of hard particles entering the chamber would be at the shoreline, at the surf zone.
I honestly cannot tell the difference between when I when I first used them to the time I service them, which is usually around the three year mark.
Out of curiosity, how long does it take to cause the wear that has been shown on the body of the regulator firs stage. I have taken apart my Atomic regulators and have found some sediments on the piston and at base of the spring. Although, I don't recall seeing any wear or scratches on the "land" part of the first stage body. However, the Zirconium plating has worn away from the second stage inlet tube on my current Z2. It's rather evident, when one is brass colored and one is gold colored. I currently dive in the Monterey of California. About the only time could fathom of hard particles entering the chamber would be at the shoreline, at the surf zone.
I honestly cannot tell the difference between when I when I first used them to the time I service them, which is usually around the three year mark.
If you flush your regs religiously after use in Monterey shore diving, you might never see more than superficial scratches on the piston land. Biennial service would clean out any resid sand particles.
If you don't flush, then the next dive will begin the process, with tiny grains lodged around the piston rim. If it's months between dives, so that crystallized salt binds everything in place, then you'll start to see scratches immediately after the next dive. The corrosion that explodes once you scratch thru the chrome anywhere, can make signif. damage occur within about 2-4 years. But as pics show, it can generally be restored IF the shop does polishing. But very few do.
If they just do a parts swap with only a wipe of the housing, then things will progress. But still, except for tropical regs, it's usually a decade before you might see a LP leak. Whether it's fixable at that point is generally a 50:50 proposition.
So with average post-dive maintenance, no - I wouldn't expect to see much at the 3 year mark.
If you don't flush, then the next dive will begin the process, with tiny grains lodged around the piston rim. If it's months between dives, so that crystallized salt binds everything in place, then you'll start to see scratches immediately after the next dive. The corrosion that explodes once you scratch thru the chrome anywhere, can make signif. damage occur within about 2-4 years. But as pics show, it can generally be restored IF the shop does polishing. But very few do.
If they just do a parts swap with only a wipe of the housing, then things will progress. But still, except for tropical regs, it's usually a decade before you might see a LP leak. Whether it's fixable at that point is generally a 50:50 proposition.
So with average post-dive maintenance, no - I wouldn't expect to see much at the 3 year mark.
scubafanatic
Contributor
- Messages
- 5,090
- Reaction score
- 914
When I had a few Atomic titanium (piston) regs serviced (annuals) @ Scubatoys, their reg tech STRONGLY recommended NOT sealing the 1st-stages with Christolube, but instead to leave them non-sealed. I took his advice on 2 of the 3 reg sets.
Similar threads
