Scubapro not having environmentally sealed first stage

[fmerkel]

Do your know that would not happen with a sealed piston?
Wonder if it much matters. Wife has a MK20. Never been sealed. Probably has 1000+ dives in Puget Sound (NW, cold) waters over 20 years. Chrome is long gone. Only leaks I ever get are around the HP piston seal, or the damn HP seat, which is a common problem with this reg. Never leaks around the piston head seal near as I can tell. Always some kind of corrosion in the areas of you photo when I over haul it.

 

[Primary]

I work on a lot of MK25s -- many from commercial accounts, large public safety agencies, universities etc., where the user has no vested interest in rinsing the reg.

Yes, many of them have signs of internal corrosion but I can think of only one instance in which the damage was so bad the piston orings wouldn't seal. Do you see that often?

 

[fmerkel]

That looks more like gouges than corrosion. Sand in the IP chamber maybe?

 

[rsingler]

@Primary , I get a lot of regs from folk that are coming back to diving, or bought stuff that had been sitting in a closet (off eBay), where slow corrosion from being put away wet really ate away at the brass.
The regs you describe are more like a violin. There's probably a side benefit to being dived hard, even if they're not rinsed. The use itself keeps parts moving, and may mitigate some of the damage shown in my photos.

However, the picture you attached is a separate issue. That's a pretty classic picture of more than one gouge from the rim of the piston head. It happens when someone is rushing to put a set back together, and doesn't take ten seconds to gently ease the piston into the cap, perfectly straight. The tolerances are so fine there, that if off center, the piston head catches on the cap. If the tech then just squeezes on the spring to "pop it into place", the piston head gouges the land in the cap that is critical to sealing. Alternatively, the gouge can occur when trying to "rock" out the piston for service. If it catches, and you force it out, you can get a deep gouge.

As long as the gouge is higher than where the piston ring rides, there's no ill effect. When it's a little deeper in the land, the reg will leak along the gouge line, and you'll see an occasional bubble from intermediate pressure air coming out of the ambient holes. Since its not a high pressure leak, the reg can usually still be dived. But you'll notice gauge pressure dropping over a half hour after the tank is turned off while the set sits.

 

[halocline]

I routinely dive with unsealed piston regulators that are 40 years old. I think the 10 to 20 year lifespan is far from accurate. I have seen one MK10 and one MK5 piston corroded to the point where I needed to replace them. That's out of several dozen examples. I have never seen an ambient chamber so corroded that it wouldn't seal.

So I don't think unsealed regulators that are well maintained will wear out any faster than sealed regulators. The truth is that very few well designed and well maintained regulators ever wear out. What happens is that manufacturers stop supporting specific models and/or unscrupulous salesmen convince customers that their regs cannot be fixed. Sometimes it is true; not thoroughly cleaning salt water out of regulators after use will definitely destroy them in time, and lots of people don't really clean their regs. I soak mine in clean fresh water for a few hours (at least) at the end of a salt water dive day. That removes the salt water from exposed threads (rinsing will not do that) and other spots where water intrusion is gradual and/or not easy to flush.

 

[lexvil]

I guess it comes down to “depends” I have a 45 year old MK 5/109 that is like new, only has 30 or so dives on it but it is old and in really good condition. I had a MK 25 that after 8 years was scored really badly but hundreds of dives mostly salt sandy beach diving.

 

[Couv]

That looks more like gouges than corrosion.

Agree.

That's a pretty classic picture of more than one gouge from the rim of the piston head. It happens when someone is rushing to put a set back together, and doesn't take ten seconds to gently ease the piston into the cap, perfectly straight.

^^^This^^^
From the pattern, it looks like someone tried to "unscrew" the piston from the cap.