Reg lockup

[NancyLynn]

I was taught in my OW class that regs were designed to fail by free-flowing rather than locking up, so I was a bit surprised when my reg locked up (no air) on a recent dive trip. Fortunately, I was at the surface just preparing to head down. I tried to take a breath, it sounded and felt like trying to breath through a tube which had a piece of rubber sucked against it and got no air. My octo worked fine.

Prior to the next dive, we swapped out the second stage and I did two or three more dives on the same assembly (with the rented second stage) it during the trip.

I went in to pick up my reg after servicing, and was told they couldn't find anything wrong with it. Fortunately, when they hooked it back up to my first stage and tested the entire assembly they discovered a first stage pressure creep - the pressure heading into the 2nd stage was way too high, and apparently that is what caused the second stage failure.

My assumption, since the sound came from the second stage, and the octo worked fine, was that the problem was in my second stage. A little disconcerting, since I like the idea of free flow far better than a lockup, but I believed I had a reliable backup in my brand new octo that seemed to work. Guess I was wrong - and lucky.

1. Short of carrying a completely independent air source, I'm interested in any thoughts as to what I could/should have noticed or done to find the source of the problem since it wasn't where I thought it was - and my octo and replacement second stage could just as easily have locked up (or gone into free flow) as the original second stage did.

2. Anyone else experience lock-up rather than free-flow related to a first stage failure?

 

[tfsails]

Assuming you have a standard "downstream" second stage, when you encounter an IP that's too high it'll merely override the poppet spring, break the seal between the poppet seat and the orifice, and free flow. Just about every brand of regulator except some Poseidons and some old Sherwoods is a downstream design.

"Downstream" means the sealing surface is downstream in terms of air flow from the first stage. The only thing keeping the poppet seat sealed air tight against the orifice is spring pressure from the poppet spring. Too much pressure from the first stage, and the poppet opens. Quite simple. And reliable.

Newer Poseidon designs and a Sherwood design that is really a Poseidon second stage use a ballon inside a cylinder which is radially drilled with holes to allow air flow. This is known as an "upstream" design. The balloon is normally collapsed and air pressure from the first stage expands it to make it seal against the inside of the cylinder. When you breathe on this second stage, the balloon collapses and air flows to the diver. If IP is too high on this reg, the balloon will only seal tighter. This reg uses a propietary hose that has a relief valve built into it and it cannot use any other type of hose.

"IP", or Intermediate Pressure, is what the first stage supplies to the second stage via the LP hose. It is usually in the area of 140 psig, but can vary by make.

I would speculate (and it's ONLY speculation) that if you had a "lockup" in your primary second stage, you had some sort of blockage either in the first stage LP port for your primary second stage, the primary LP hose, or in the inlet side of the stage where the orifice lives. You may have inadvertently eliminated the source of any LP port blockage when you installed the rental second stage. The source may still be inside the first stage and just not blocking the port any more. The fact that your octo worked normally makes me believe that the IP was normal and the first stage worked properly. If I were you I would take that reg back to the shop and have them take it apart and make absolutely sure that the primary second stage's hose is not blocked and make sure that the inlet is open and you can see through it. I would also have them make certain that there are no foreign objects inside the LP side of the first stage.

It is NOT normal for a second stage to fail "closed". They are designed to fail open.

I hope this helps. Good luck and keep me posted.

 

[NancyLynn]

The fact that your octo worked normally makes me believe that the IP was normal and the first stage worked properly.

Thanks.

The IP is not normal. I watched it creep to 200 psi. So there is a failure of the 1st stage - even if it was not the ultimate cause of the second stage failure. It is being serviced and an upgrade kit installed to replace non-metal parts with metal parts. (Apparently making my SP MK16 equivalent to an MK 17.)

When I pick it up, I will ask if they took it completely apart and looked for anything which might have been blocking it. They are doing the annual service while they have it in their hands - on the early side, but better safe than sorry.

 

[redacted]

I would not be comfortable diving that regulator until the cause of the lock-up is understood and corrected. IP creep and a rebuild of the first stage is not a reasonable explanation.

What 2nd stages are you using for your primary and octo? When you replaced your primary with the rental reg, did you also replace the LP hose?

BTW, I've bought regs from ebay, and inspected/tested and dove them without doing a complete service; so it really isn't too hard for me to be comfortable with a regulator.

 

[NancyLynn]

I would not be comfortable diving that regulator until the cause of the lock-up is understood and corrected. IP creep and a rebuild of the first stage is not a reasonable explanation.

Agreed, as to the first. This incident has convinced me that I need to understand exactly how my reg works - if I can't find service manuals online, I'll go hunt through the patent files.

I don't always service my own bike, but I certainly know how - this is life support equipment so I should know even more.

What 2nd stages are you using for your primary and octo? When you replaced your primary with the rental reg, did you also replace the LP hose?

SP R390/R190 and no. At the time, it seemed so clear to us that the problem was within the second stage that we just swapped out the second stage.

 

[DA Aquamaster]

Little or no flow of air from an R190/R190 second stage could occur if the working range were restricted through poor adjustment and / or if the lever were blocked with a piece of foreign matter or ice inside the reg.

Excessive IP would cause the reg to fail downstream resulting in a freeflow, not cause it to stop delivering air.

In some designs it is possible in very rare cases for the lever to slip off the poppet if the tabs on the elver are damaged or misalingned, but that is not possible on the R190/R390 poppet design as it is all one piece with the seat one the end of the poppet stem and the lever on the other end of the stem with a spring in the middle holding the seat against the orifice. The tilting of the lever simply compresses the spring and lifts the seat off the orifice.

The only way for it to fail closed (other than a foreign object restricting lever movement) would be if the nut on the end screwed itself off. The nut used is a nyloc fastener that will not normally unscrew by itself. SP specs require "a maximum of one poppet carrier thread showing through if used for a primary regulator" , "a maximum of two poppet carrier threads showing through if used for an octopus regulator", and "a maximum of three poppet carrier threads showing through under all circumstances".

The problem with this is that it specifies a maximum but not a minimum for thread protrusion and more or less encourages fewer threads showing past the nyloc fastener. If screwed too far out on the poppet stem, to the point that the threads are not fully engaged in the nyloc portion fo the fastener, it may be possible for the nut to screw itself off the poppet far enough to lower the lever to the point it will not lift the seat off the orifice.

Personally, I ensure one full thread shows past the end of the nyloc fastener as I am more concerned that it stay put than I am with gaining a bit lower inhalation effort.

 

[NancyLynn]

Little or no flow of air from an R190/R190 second stage could occur if the working range were restricted through poor adjustment and / or if the lever were blocked with a piece of foreign matter or ice inside the reg.

This went from a fairly normal breathing effort to a hard stop, accompanied by what sounded and felt like I was sucking a piece of rubber against a breathing tube.

No ice, for sure. The water temperature was 78 degrees

This series of around a dozen dives was the first use after its annual service, so it should have been well adjusted - and I had no problems for the 10 or so dives ahead of the problem dive. The second stage was taken apart as soon as we got back from the dives (in which I used the borrowed second stage), and the owner of my LDS could not find any debris (or other reason for the lockup).

Excessive IP would cause the reg to fail downstream resulting in a freeflow, not cause it to stop delivering air.

Yeah, that's what they told me during training - kind of a rude surprise when I encountered the opposite problem.

Personally, I ensure one full thread shows past the end of the nyloc fastener as I am more concerned that it stay put than I am with gaining a bit lower inhalation effort.

I don't have the second stage in front of me so I can't see specifically what you are referencing (it's still hanging out at the shop) but from what you are saying regarding inhalation effort, I had it set in the direction you are suggesting (higher inhalation effort, rather than lower).

 

[ReefHound]

This series of around a dozen dives was the first use after its annual service, so it should have been well adjusted - and I had no problems for the 10 or so dives ahead of the problem dive. The second stage was taken apart as soon as we got back from the dives (in which I used the borrowed second stage), and the owner of my LDS could not find any debris (or other reason for the lockup).

So your reg locked up right after service? Sounds like somebody assembled it incorrectly or severely misadjusted it. Did you have it checked out by the LDS that did the original service? If so, sounds like a CYA job on their part.

 

[NancyLynn]

So your reg locked up right after service? Sounds like somebody assembled it incorrectly or severely misadjusted it. Did you have it checked out by the LDS that did the original service? If so, sounds like a CYA job on their part.

Time-wise, it wasn't right after. I just didn't get a chance to dive for several months, so it was the first series of post service dives which took place about 8 months after service. It locked up on about the 10th dive in a series of around a dozen dives over a 5 day period. Worked fine for the first nine or so.

After finding what appears to be a good explanation of how the second stage functions about 2/3 of the way down this page: Howstuffworks "Regulators and Scuba Breathing Apparatus"
I'm having a hard time envisioning anything that could make the sound and feel of the failure - short of the impossibility of moving the diaphragm on the back side of the lever so it blocked the outlet to the mouthpiece. I may just need to take it apart and play with it until I'm comfortable with it once I get it back.

 

[ReefHound]

I wouldn't take it apart yourself unless you have the proper tools and knowledge. Since this is your primary reg, you're just asking for more trouble. Practice on an old reg to learn.

You didn't mention anything about cold so I'm guessing it couldn't have been blocked by ice. And I'll assume you know for sure the air was actually on and the hose wasn't kinked. It could have been debris in the first stage blocking the port. I'm still leaning towards improper parts or assembly during the original service. I don't know anything about your LDS but I can see where an LDS would not want to admit they seriously botched a service job that could have had catastrophic consequences if they could quietly fix things and ensure it doesn't happen again.