Are viton o-rings really necessary?

[halocline]

It was not a failed oring, nothing failed per say. It was a lack of lubrication on a dynamic piston oring that cause the HP seat to stick open. To prove it, cleaning and then lubricating just the section in question yielded a fully functional regulator. After testing the failure mode the reg was torn down and rebuilt.

There is absolutely no way that lack of lubrication on the HP o-ring in a balanced piston reg would cause the valve to stay open, period. Whoever told you that pulled one on you. This is assuming you are referring to the SP balanced piston design, which BTW is one of the most copied 1st stage design in history.

I know how these regs work, and I know that you are wrong. There can certainly be some IP rise caused by friction at the o-ring, but never "stuck open." There's 3000 PSI pushing that sucker closed on a full tank.

If you had a severe free flow that was caused by an IP spike, it happened because either something got on the seat to prevent a seal, the seat material failed, or the piston cracked.

Try to get your facts straight before insulting those who are more knowledgeable about this topic.

And what's "comical" is your insistence that regulator failure is life threatening and can be prevented by regular service, and that we DIYers are risking our lives. Well, you're the one that had the reg failure, and you seemed to have survived it just fine.

 

[fppf]

See Matt this is where your wrong, I don't have anything against DIYers. I have never said anything against DIYers, just that if you do it, do it right. And any problem that can be solved or prevented is one less thing to cause an issue in the water, where it can lead to other problems. There where a fair amount of deaths last season with gear related items. I don't understand why the DIYer thinks there smarter then the designer.

I did the analysis myself, and you very clearly A) did not read my last post, the one where I said it is a balanced diaphragm design; and B) don't understand regulators by your post. Just because there is 3000 PSI of cylinder pressure, or 500 PSI for that matter, does not mean there is "3000 PSI holding that sucker closed"

So, for the sake of being clear. With a balanced diaphragm design with an upstream HP valve, the forces are balanced on the seat and has very low seat forces. When pressure drops the sensing diaphragm will depress into the HP valve and open it, pushing it into the HP chamber. Now, as the pressure in the regulator increase it will push the sensing diaphragm and the transfer pin up, but because there is now high pressure across the face of the valve seat it needs a little help to be able to close. This is where the lower (smaller) return spring comes into play. This spring pushes the HP seat closed. So you see, there really is not a lot of acting forces working on the valve. Now, when you take a deep draw on the reg with a steady flow rate the HP valve will open and then stay open during the flow. This causes the valve to open and then hold at a position. If you understand piston seals and designs you will know that break out friction is much higher then running friction. In this case the additional break out friction from the dried out seal was to much for the return spring to over come. Which caused the valve to stick open, which caused loss of regulation, which popped the second stage to free flow.

Now when tearing down this reg you pull the HP assembly out first, which has the HP seat, return spring and balance chamber. Upon inspection, when manually depressing the HP seat into the balance chamber and releasing it, the HP seat did not return, it stuck. When the seal was inspected it showed signs of increased wear and all the lubrication was displaced. For testing purposes the dynamic seal was lubricated, and placed back into the regulator for bench testing. No other parts of the reg where touched, and the reg returned to a functional state.

After the functional test, the rest of the regulator was torn down. The filter was clean and clear and NO FOD was found in the regulator. The HP seat was intact and in good condition.

So you can see, it is clearly possible for a sticky seal to cause a free flow.

 

[halocline]

It was not a failed oring, nothing failed per say. It was a lack of lubrication on a dynamic piston oring that cause the HP seat to stick open.

This is where you said dynamic piston o-ring. Those exist in piston regulators. In a later post you said it was a diaphragm reg. Which was it? If you're not sure what kind of reg you have, I'm sure you could take it to the shop, they'll tell you. Then you can come back here and keep insulting people.

 

[halocline]

I find it VERY comical that the same people proposing to stretch service life also propose to use the regulator design that most needs the service. The lubercation on pneumatic piston seals only lasts so long, when its gone, you have issues.

Since you're referring to those of us who are not advocating annual service, many of whom are using SP balanced piston regs, AND you keep talking about "pneumatic piston seals" it's easy to see why one would think that you were talking about a balanced piston regulator.

Your insulting, condescending remarks might be a little more tolerable if they contained intelligent, factually correct statements instead of confusion.

 

[fppf]

So lets continue the education

Because you bring up Scuba Pro, I would assume you have experience with them. I personally do not own or have taken apart a Scuba Pro regulator, I'm just using this as an example of a typical balanced DIAPHRAGM regulator.

Now, lets take a look at the design of the MK17, specifically the balance chamber and HP seat/Poppet. So, lets look at the "HP Valve" at the top is the actual seat that seals to the "Orifice". The bottom slides into the "Bal. Chamber". Now, the bottom section of the "HP Valve" forms a piston. and the "Bal. Chamber" is a cylinder for that piston. Then there is an o-ring that seals the "HP Valve" stem section into the "Bal. Chamber". This seal is dynamic because the "HP Valve" must move up and down to open and close. Thus forming a dynamic piston seal, even though the main sensing element is a diaphragm. Now, even more important is that the seal stresses on THIS dynamic piston seal are going to be MUCH higher then the dynamic piston seal your thinking of, the one that senses on a "Piston Regulator". This is because the pressure delta with a full cylinder is very high, the inside of the balance chamber is at the IP pressure and the pressure around the "HP Valve" is cylinder pressure. Making a pressure delta of over 3,000 PSI at times. Where in a standard "Piston Regulator" the pressure delta is very low (in relative terms) at IP pressure vs ambient.

Hope that clears up which "dynamic piston seal" we are talking about here.
Maybe you guys should come over to my house and I can give you in depth design reviews of regulators. We can even go over acting forces and how designers cancel them for better regulations. I'm not trying to insult anyone, but don't come on here and call me a lair. Your just proving the point that even some "Dive Professionals" really don't understand regulator design.

This is also why I did not want to go into the failure analysis, its very technical and most don't understand it anyway and get confused.

 

[ams511]

The recommendation to have a scuba regulator serviced annually has been around since the early days of scuba. However, given advances in manufacturing and materials science I would assume the materials used now are much better than in days gone by. For example autos last longer now without needing repairs or rusting out than they did back in the 1970's. So the question is why have not the service intervals for scuba also increased?

When I lived in Pennsylvania the owner of the dive shop (since went out of business) was an artist with a regulator. He could tune a 15 year old Sherwood Magnum so it would breath as well as an Apeks. I do own both so I can make the comparison. The problem is technicians with that skill are few and far between. Most technicians are the slap the parts in sort of person. People who took a one-day seminar in regulator repair and probably would rather be diving on a boat than fixing regulators.

My point is that if you are lucky enough to have an "artist" work on your regulator then fppf is correct. Although he even admitted stretching the service intervals. However, if you are dealing with a "wrench turner" then the other posters point of view is correct.

 

[ams511]

I have another thought. I have no personal experience sky diving but from my understanding is that you are always taught how to pack a parachute because no sane person would trust such an important job to a stranger. Now should not the same thing apply to regulator repair?

 

[knowone]

Is there even REALLY a difference between viton o-rings and the generic, your gear will blow up if them come in contact with 02 o-rings? Or is that just yet another way for them to overcharge you for something that's not really necessary?

Looking at them side by side I can't even see a difference. If I was to dump all my BAD o-rings in the pack with the vitons, they'd get mixed up, and I'd have no idea which ones I was using. S**t is there even such a thing as vitons or did they just make up a word and put in on the package. How do do I even know that pack of vitons are even vitons other than just the magic word on the box...considering they look the same as the other ones?

Jam your thumb in your valve and crack it. EPDM.

 

[redacted]

If I found a dynamic o-ring that was so lacking in lubricant that the resultant friction forces overpowered the other designed operating forces, I'd be wondering if it had been properly lubricated when assembled. Especially in this case where it is the dynamic o-ring on a balanced diaphragm 1st that should never see anything but gas and not be subjected to washout by water as most other dynamic scuba o-rings are.

I'd suspect this failure was caused by improper maintenance rather than lack of maintenance.

 

[fppf]

There where traces of lubrication in the bore and at the ends of the piston. It had just dispersed over time. I will agree its a rare failure mode. But from a systems design view, the hardest thing with pneumatics is keeping the dynamic seals lubed.