Intermittent "stiff" breathing on vintage reg

[MiddleCoaster]

I use a 1979 AMF Swimaster MR 12-II reg that I had rebuilt about a year ago. Have dived about 20-30 hours on it in the past year.

Lately, it occasionally breathes "stiff" for a while -- meaning that breathing effort is increased noticably -- but not contsistently. Makes no difference if it's the wreck of the Duane at 108' in strong saltwater current or in 5' of fresh water assisting DSD in the local pool.

The unit is carefully and thoroughly rinsed and dried after each use.

LDS owner speculates that it is a weak/weakening main first stage spring.

What are your thoughts? Any other possible causes?

Short of another $200 rebuild, what should be done?

Safe to continue use?

 

[JKPAO]

Sometimes they do wear out! A new spring may be the answer , but while your in there a couple of o new o rings might not hurt either
See you topside! John

 

[LeadTurn_SD]

I use a 1979 AMF Swimaster MR 12-II reg that I had rebuilt about a year ago. Have dived about 20-30 hours on it in the past year.

Lately, it occasionally breathes "stiff" for a while -- meaning that breathing effort is increased noticably -- but not contsistently. Makes no difference if it's the wreck of the Duane at 108' in strong saltwater current or in 5' of fresh water assisting DSD in the local pool.

The unit is carefully and thoroughly rinsed and dried after each use.

LDS owner speculates that it is a weak/weakening main first stage spring.

What are your thoughts? Any other possible causes?

Short of another $200 rebuild, what should be done?

Safe to continue use?

Any decrease in the breathing performance of your regulator needs to be evaluated. Don't continue to use it until the cause of the "stiff breathing" is tracked down and corrected.

I'd start by measuring the 1st stage IP, especially the IP drop and recovery with inhalation. There is a possibility it is a 2nd stage problem, but I'd guess the problem is probably in the first stage. Spring, friction from o-rings that are worn or improperly lubed.... just guessing until the reg is inspected and torn down however.

Let us know what the problem turns out to be.

Best wishes.

 

[SwimJim]

I use a 1979 AMF Swimaster MR 12-II reg that I had rebuilt about a year ago. Have dived about 20-30 hours on it in the past year.

Lately, it occasionally breathes "stiff" for a while -- meaning that breathing effort is increased noticably -- but not contsistently. Makes no difference if it's the wreck of the Duane at 108' in strong saltwater current or in 5' of fresh water assisting DSD in the local pool.

The unit is carefully and thoroughly rinsed and dried after each use.

LDS owner speculates that it is a weak/weakening main first stage spring.

What are your thoughts? Any other possible causes?

Short of another $200 rebuild, what should be done?


Safe to continue use?

$200.00 for a rebuild on an MR-12?? That's totally insane! Find a different LDS. Log on to Vintage Scuba - Vintage Scuba Diving - Vintage Scuba Gear - vintagedoublehose.com and look for Greg Barlow. He is an expert on MR-12 regs.

 

[Graeme Tolton]

$200 for any reg is insane!

 

[herman]

I would not suspect the spring, more likely a balance chamber issue or some corrosion if its the first stage or something amiss in the second stage. Before digging into the reg I would try this. While diving- in a safe place please- get the problem to occur again and immediately swap to your oct, if the problem goes away, swap back to your primary. If the problem is very intermittent you may have to do it several times. If the problem shows up in both second stage then it's a first stage issue, if it follows one second stage, it's a second stage issue. Now that you have the stage identified, you can start looking for the problem.....and $200 had better of been to replace every thing on the reg- complete rebuild with new everything and new hoses. If not, find a new shop or better yet learn to do it yourself.

 

[herman]

I just remembered another possible cause, I have never seen but have heard about it causing similar problems, It is possible you have a bad hose. A little flap of rubber comes loose inside the hose and intermittently blocks the flow....I would swap the hoses around or just replace it if its old. And if it was recently replaced that does not mean a manuf defect was not in it and has just shown up.

 

[MiddleCoaster]

The IP is right on and IP recovery is good.

All O-rings, diaphragms and seats were replaced in the 2009 rebuild. Actual cost was $156 including shipping to Vintage Scuba Supply in Selma, OR.

The suggestion to swap out 2nd stages (use octo when primary breathing gets "stiff") is a good one, and will try that this coming weekend.

I suspect it may be a second stage tuning issue. When I inhale normally during "stiff" breathing the problem persists, but a strong inhale delivers all the air I need -- and seems to overcome a resistance to breathing. In my mind's eye, I can see the second stage valve lever being somewhat resistant to operating until really called upon.

Also, I notice that the purge seems weak on this second stage, which may indicate adjustment needed.

 

[LeadTurn_SD]

If you can swap out 2nd stages (with a known "good" second stage from a different regulator), that might help diagnose the problem.

Good luck, and let us know what you find.

Best wishes.

 

[halocline]

The IP is right on and IP recovery is good.

All O-rings, diaphragms and seats were replaced in the 2009 rebuild. Actual cost was $156 including shipping to Vintage Scuba Supply in Selma, OR.

The suggestion to swap out 2nd stages (use octo when primary breathing gets "stiff") is a good one, and will try that this coming weekend.

I suspect it may be a second stage tuning issue. When I inhale normally during "stiff" breathing the problem persists, but a strong inhale delivers all the air I need -- and seems to overcome a resistance to breathing. In my mind's eye, I can see the second stage valve lever being somewhat resistant to operating until really called upon.

Also, I notice that the purge seems weak on this second stage, which may indicate adjustment needed.

You're probably right about it being the 2nd stage, but unless you measured the IP and recovery while it was breathing stiff, you don't really know if it's associated with the problem. The mainspring in the 1st stage does regulate IP; if it gets weak, you can't get the IP stable, especially in the higher range where you might want this reg to be. But, that's usually not an intermittent problem. A while back a few of the doublehose crowd were having problems with IP stability in the higher ranges; I had that problem with a DA aquamaster. Someone (maybe herman?) found appropriate new springs and it solved the problem. But those were never intermittent issues; they showed up right away on the IP gauge.

You should consider taking this reg apart and fixing the problem yourself. You can get Vance Harlow's excellent book on regulator repair, and all the free advice you'd ever want and some you probably don't here on this forum.