Fail open? Not always

[AfterDark]

Recently I sent my rig up and checked my MK5 to be sure it was working. Pressed the purge and very little happened, a small amount of air came out. Tried to breath NOTHING! These, like most regs are suppose to fail free flowing. Apparently if a mindless tech with cranium rectal inversion installs a new style poppet and an old style spring it will fail closed. Glad it happened on land. The other time it happened with a different reg it was at 70fsw, don't want a repeat of that! Goes to show you even the most reliable piece of equipment can be made dangerous by someone dumb enough.

 

[Fishpie]

Probably a shuttle and lever problem.....tabs on the shuttle didn't engage with the lever.....assuming we're talking 109 or BA here.

 

[redacted]

Recently I sent my rig up and checked my MK5 to be sure it was working. Pressed the purge and very little happened, a small amount of air came out. Tried to breath NOTHING! These, like most regs are suppose to fail free flowing. Apparently if a mindless tech with cranium rectal inversion installs a new style poppet and an old style spring it will fail closed. Glad it happened on land. The other time it happened with a different reg it was at 70fsw, don't want a repeat of that! Goes to show you even the most reliable piece of equipment can be made dangerous by someone dumb enough.

Were both occasions related to the same tech?

Another reason I like to do my own and spend quite a bit of time inspecting my work. Whenever I change a poppet, I like to assemble, adjust, and inspect the reg with the cover removed so I can better see what is going on. It also lets me evaluate what happens when the cover is installed.

Make you appreciate the alternate.

 

[John C. Ratliff]

Recently I sent my rig up and checked my MK5 to be sure it was working. Pressed the purge and very little happened, a small amount of air came out. Tried to breath NOTHING! These, like most regs are suppose to fail free flowing. Apparently if a mindless tech with cranium rectal inversion installs a new style poppet and an old style spring it will fail closed. Glad it happened on land. The other time it happened with a different reg it was at 70fsw, don't want a repeat of that! Goes to show you even the most reliable piece of equipment can be made dangerous by someone dumb enough.

You mention the MK5, but that's the first stage. The second stage is a downstream valve, and if there were a first stage failure, the air would blow through. But if, as discussed above, the levers were not set to engage the poppet, then the poppet could not be moved off the valve seat, which would cause your symptoms. But this is not a "failure" of the valve. It is improper maintenance and assembly. In short, it cannot be dived in this condition at all. I don't think this could happen to a functioning regulator while in use at depth.

SeaRat

 

[halocline]

I wonder if you had an old style poppet that was replaced by a new one, and that there was an incompatibility issue between the new poppet and old lever. The spring shouldn't make any difference, although if you had the unbalanced poppet and the guy replaced it with a balanced poppet but still used the heavy spring, I wonder what would happen there. The heavier spring for the unbalanced poppet is a larger diameter, but I think it would still catch on the new s wing poppet, just making it way harder to breathe. You'd have to be a pretty sketchy tech to make that mistake, anyway.

Maybe the guy installed the poppet upside down, so the lever didn't catch on the feet. Either way, another good reason to do your own reg maintenance.

The MK 5 was sold as a reg set with a 109, if I remember right, the whole thing was sold as a "MK 5."

 

[Akimbo]

Did the "technician" actually test it after "upgrading" it or did the lever disengage afterwards? Or are you talking about the main string in the first stage?

 

[redacted]

The second stage is a downstream valve, and if there were a first stage failure, the air would blow through. But if, as discussed above, the levers were not set to engage the poppet, then the poppet could not be moved off the valve seat, which would cause your symptoms. But this is not a "failure" of the valve. It is improper maintenance and assembly. In short, it cannot be dived in this condition at all. I don't think this could happen to a functioning regulator while in use at depth.

SeaRat

I'm pretty sure AD is talking a 109 and I have no reason to disbelieve his claim of failed closed at 70 ft. If the poppet slips past the lever arms, then that would be the expected failure mode. I had one 109 that did not take the new duro poppet well. When I initially assembled it (with the cover off), the lever height was way too high. After installing the cover, it took more than 2 full turns on the orifice to again seat and it breathed like crap. I suspect that left the feet at a rather drastic angle with little room for error in engaging the poppet. (In my case, I bent the feet and now I'm no longer sure which 109 was the problem. But that was a half-assed solution.) I suspect that situation could well have led to the failure AD described with no air available through that 2nd.

A good tech should catch such a problem but not all shops have good techs. I have never seen anything in Scubapro documentation alerting tech to be on the lookout for such a problem. It is something I look for every time I put another 109/156 back into service.

 

[AfterDark]

I wonder if you had an old style poppet that was replaced by a new one, and that there was an incompatibility issue between the new poppet and old lever. The spring shouldn't make any difference, although if you had the unbalanced poppet and the guy replaced it with a balanced poppet but still used the heavy spring, I wonder what would happen there. The heavier spring for the unbalanced poppet is a larger diameter, but I think it would still catch on the new s wing poppet, just making it way harder to breathe. You'd have to be a pretty sketchy tech to make that mistake, anyway.

Maybe the guy installed the poppet upside down, so the lever didn't catch on the feet. Either way, another good reason to do your own reg maintenance.

The MK 5 was sold as a reg set with a 109, if I remember right, the whole thing was sold as a "MK 5."

Recently I sent my rig up and checked my MK5 to be sure it was working. Pressed the purge and very little happened, a small amount of air came out. Tried to breath NOTHING! These, like most regs are suppose to fail free flowing. Apparently if a mindless tech with cranium rectal inversion installs a new style poppet and an old style spring it will fail closed. Glad it happened on land. The other time it happened with a different reg it was at 70fsw, don't want a repeat of that! Goes to show you even the most reliable piece of equipment can be made dangerous by someone dumb enough.

Hey Matt you don't need to wonder its right there in my 1st post. I had 20 dives on that reg since the service. The only thing I noticed was the adj. felt harder to turn than usual. It wasn't an upgrade it was regular service done by someone I'd never used before and wouldn't use again. The guy that found the problem was the guy that has been working on my MK5 since he was a teen, his father taught him. His dad was one of the 1st scubapro dealers in NE. What he said to me was the poppet slipped off the spring and jammed against the opening. I know it's not a normal failure but a man made one but just the same I'm glad it didn't happen in the water.

Of course all that is in my OP. John I bought the MK5 in 1968 it had a 1st and 2nd stage they called it a MK5 that's what I call it. I'm not sure what your unclear about.

 

[halocline]

Apparently if a mindless tech with cranium rectal inversion installs a new style poppet and an old style spring it will fail closed....
Hey Matt you don't need to wonder its right there in my 1st post. I had 20 dives on that reg since the service. The only thing I noticed was the adj. felt harder to turn than usual....
What he said to me was the poppet slipped off the spring and jammed against the opening.

There are two "new style" poppets; the unbalanced G200 and the balanced G50 or "S-wing" poppet. If you had a 109, not balanced, the standard rebuild would be to use a new unbalanced (G200, "duro" poppet) which would be perfectly compatible with the "old" style spring. (Actually, it's more accurate to refer to the springs as the heavier "unbalanced" or G200 spring, and the lighter balanced or G250 spring)

The only spring incompatibility would be as I described, a tech installing a balanced "S-wing" poppet but keeping the heavier spring. Is that what the guy did? If so, that's not someone you want working on your reg, regardless of what his Dad taught him.

Further, if the poppet "slipped off" the spring, it would result in free flow, not no-flow. What I think you mean is that the poppet slipped off the lever, as Awap was describing. Spring and lever are two different parts. There are definitely some compatibility issues between some of the older levers and the duro poppet.

 

[AfterDark]

There are two "new style" poppets; the unbalanced G200 and the balanced G50 or "S-wing" poppet. If you had a 109, not balanced, the standard rebuild would be to use a new unbalanced (G200, "duro" poppet) which would be perfectly compatible with the "old" style spring. (Actually, it's more accurate to refer to the springs as the heavier "unbalanced" or G200 spring, and the lighter balanced or G250 spring)

The only spring incompatibility would be as I described, a tech installing a balanced "S-wing" poppet but keeping the heavier spring. Is that what the guy did? If so, that's not someone you want working on your reg, regardless of what his Dad taught him.

Further, if the poppet "slipped off" the spring, it would result in free flow, not no-flow. What I think you mean is that the poppet slipped off the lever, as Awap was describing. Spring and lever are two different parts. There are definitely some compatibility issues between some of the older levers and the duro poppet.

You've got it right except for the tech. The son of my friend FOUND the problem after I brought the reg to him. The tech that CAUSED the problem was someone I'd never used before and wouldn't use again. I could have missed understood the finer points but the jest of the problem was a "new" style balanced poppet installed with the old heavier spring however the combo failed it failed closed and pissed me off.

I also had to solder the one of the "legs" that the exhaust check valve sits on. I'll be bringing it back to my fiends son Sat so he can put it together and adjust it.

Thanks all for all the input.

... I had 20 dives on that reg since the service. The only thing I noticed was the adj. felt harder to turn than usual. It wasn't an upgrade it was regular service done by someone I'd never used before and wouldn't use again. The guy that found the problem was the guy that has been working on my MK5 since he was a teen, his father taught him. His dad was one of the 1st scubapro dealers in NE.