Scubapro Mk11 lack of environmental sealing?

[Geo7]

One has to weigh pro's and con's, as sealed diaphragm 1st stages tend to be bigger and heavier. The Mk11 is incredibly small and light and a great performer. The Poseidons have been the go-to cold water regs for decades, and few people bothered sealing them. In theory you can just rinse a Mk17 and store it away, but in reality the 2nd stage needs soaking etc., so an unsealed diaphragm reg does really well.

 

[BoundForElsewhere]

the titanium mk11's have anti-corrosion superpowers.

 

[Geo7]

Don't get me started, I love titanium...

 

[halocline]

So basically:

• Sand in the Mk25 (piston reg) ambient chamber can cause damage since an o-ring is exposed there

This may be theoretically true but I have never seen damage from sand in a SP piston 1st stage, regardless of model. What I have seen is corrosion on the exposed side of the piston head from salt water that has dried in the ambient chamber. It's important to fully rinse (actually soak) the ambient chamber of a piston reg after a salt water dive.

In a non-sealed diaphragm reg, there are metal parts exposed to the elements, namely a spring and the cap that holds it in place. So you need to rinse that too. But the main reason to really soak any 1st stage after salt water use is that all regulators have exposed threads; parts that are either not subject to pressure differential or are sealed by o-rings on the inward side of the threads. Salt water will creep into these threads during diving, and the only way to fully get rid of that is to soak, not dip, the 1st stage in clean fresh water after salt water dives. This allows the fresh water to slowly penetrate the threads, just like the salt water did on an ocean dive, and then the fresh water will dilute the salt out by osmosis.

Many people don't do this, and as a result after a season of diving there is verdigris and corrosion built up on these threads. If you service your regs regularly, then it's not a disaster, just sometimes harder to get things apart. Once apart, everything gets cleaned. But I like to keep my regulators very clean and I don't want to take them apart every season (they last far longer between services) so I soak after salt dives. I use old, non sealed SP piston 1st stages, often for 4-5 years between rebuilds, and they look great when I take them apart.

 

[lexvil]

I have seen and had unsealed piston damage in the often silty diving off of the California coast, it takes along time, the abrasion causes chrome loss and then the corrosion really gets a grip, soaking and rinsing becomes even more important once at this stage.

 

[Geo7]

Yup, I agree with both of you: In clean blue water (vacation diving, or the Mediterranean, where I lived before), a Mk25 might last "forever" with diligent soaking and no neglected maintanence. Here in SoCal now, I had to restore pistons already, and basically follow rsingler's and lexvil's advice now. Still love piston 1st stages btw...

 

[halocline]

Yup, I agree with both of you: In clean blue water (vacation diving, or the Mediterranean, where I lived before), a Mk25 might last "forever" with diligent soaking and no neglected maintanence. Here in SoCal now, I had to restore pistons already, and basically follow rsingler's and lexvil's advice now. Still love piston 1st stages btw...

I'm curious how sand can cause piston degradation in a MK25. The piston head is plastic, there's a 'wiper' o-ring that keeps any debris away from the LP o-ring, and there are bushings keeping grit away from the HP o-ring.

I could theoretically see very sandy water irritating the wall of the ambient chamber, but I don't see how it could damage the piston. The piston edge (that's what gets restored in rsingler's great article) only gets wet in the event of flooding. I think any damage there is usually the result of careless handling during rebuild, or maybe a really dirty fill, or I guess just lots of time and some oxidation. The shaft can get glazed where it goes through the HP o-ring, but I've never seen deep scratches on one.

What I have seen, several times, is corrosion on the underside of the piston head, sometimes exasperated by shims or bushings trapping water underneath, and pitting in the ambient chamber wall. But that's from salt water, and maybe that's more what you are referring to.

 

[rhwestfall]

abrasive material (sand/silt) on the body walls abrading the surface.....

 

[rhwestfall]

pitting in the ambient chamber wall

yep, this!

 

[Geo7]

I'm curious how sand can cause piston degradation in a MK25. The piston head is plastic, there's a 'wiper' o-ring that keeps any debris away from the LP o-ring, and there are bushings keeping grit away from the HP o-ring.

I could theoretically see very sandy water irritating the wall of the ambient chamber, but I don't see how it could damage the piston. The piston edge (that's what gets restored in rsingler's great article) only gets wet in the event of flooding. I think any damage there is usually the result of careless handling during rebuild, or maybe a really dirty fill, or I guess just lots of time and some oxidation. The shaft can get glazed where it goes through the HP o-ring, but I've never seen deep scratches on one.

What I have seen, several times, is corrosion on the underside of the piston head, sometimes exasperated by shims or bushings trapping water underneath, and pitting in the ambient chamber wall. But that's from salt water, and maybe that's more what you are referring to.

Ah, good catch, these actually were two monel pistons on two Atomic T2X (no wiper O-ring, nor bushings) that I got second hand. One unsealed in So-Cal that probably had salt and fine silt degrading the monel piston (at the HP-o-ring area), and the other was sealed, but there was no Christolube at all in there, only trapped salt, so in that case it was so called "crevice corrosion" that monel is susceptible to if salt is trapped on it. Both pistons polished nicely to almost like new condition using @rsingler method posted before, but applied to the HP piston sealing surface. The titanium was fine, so you are right that it was salt and not sand. When I see how much sand is in the water here, I still prefer to seal my Atomic 1st stages, and at the same time I recommend to a friend in Florida to leave hers unsealed.