Scubapro MK 5 1st-stage leak, probable cause and repair ?

[scubafanatic]

One thing I have noticed when leak-testing regulators in the tub is that sometimes it takes a few minutes for every bit of air to escape the ambient chamber. Is it possible that the bubbles you're seeing are just that? I guess if you shake and roll the tank around a bit and then leave it for several minutes, then come back and you find a steady bubble stream, that's different. But a few times I have submerged regs in the tub and thought I saw a slow leak, when after a few minutes it stopped.

Unfortunately you might have a scratch in the HP o-ring journal, which would really suck. That means goodbye IMO, that's one area where you really don't want to tolerate any leak. I guess you could try to look in there with a magnifying glass and a strong light, maybe you can see something. Or maybe it's just a matter of really completely cleaning the area, making sure every remnant of grit, grease, and dust is gone, cleaning up the piston shaft with some micromesh, and carefully installing a new 90 duro o-ring.

But these are all wild-ass-guesses.

I'm pretty confident it's not the first scenario, the bubbles are 'timed' (constant at same time interval between bubbles) and long lasting with no reduction in size or number as time passes. Could be the 2nd option, guess I'll find out soon, I plan to ship them out for inspection/service in the next 2 weeks and I'll see what happens.

 

[redacted]

I'm pretty confident it's not the first scenario, the bubbles are 'timed' (constant at same time interval between bubbles) and long lasting with no reduction in size or number as time passes. Could be the 2nd option, guess I'll find out soon, I plan to ship them out for inspection/service in the next 2 weeks and I'll see what happens.

Unfortunately, many service facilities are better at simply swapping parts than they are a troubleshooting problems. In the case of a Mk5, lack of parts may well result in the shop declaring it unrepairable. Most will charge you the same price. This is a DIY opportunity.

 

[jwelburn]

The most likely scenario is a nicked o-ring or scratch on a sealing surface. There is one other issue I've seen, which is less common. I got one mk-5 from an eBay sale that had a very similar symptom. It was a spec hole model which had sat for years before being sold. The piston had corroded where the spring makes contact with it and air was leaking straight through the piston. My assumption is that it had sat for those years after not being properly rinsed. At least it was cheap! I was able to get another piston and all is well.

Hope yours is just a nicked o-ring!