balanced diaphragm vs. balanced piston

[mddolson]

Rockhound, I'm not sure if you're coment was directed at my repy or not. Let my clarify:

When I stated:
" If you dive in sandy silty water or if you're not as conciensious about rinsing the salt water out, then there is a higher risk of a malfunction. Sand, grit, dirt or salt crystals can score the shaft of the piston or orings and cause a leak" , I was pointing out the fundimental differences in design. I was not implying that Ballanced Piston regs aren't good for salt water.
Just stating fact: If NOT PROPERLY RINSED, the piston design is more prone to damage from contamination, which can be salt crystals, sand, grit and other debris. Anyone who looks after their equipment, rinsing with fresh water after dives will likely see no problems.

I am in full agreement with you as well :" The key , as someone pointed out, is good and regular service to your entire rig".


Mike D

 

[Rockhound]

Mike,

Don't take offense. My post was not directed at you or what you wrote. You and I are on the same page.

I AGREE that proper rinsing of equipment, any equipment, after any dive is a good practice, particularly with piston stages. Conventional "open" pistons are directly exposed to the water and theorectically more susceptible to contamination than sealed designs. It just that I disagree that they are any more "finicky" overall than diaphragm based 1st stages.

What I have read here and heard from others is that some dealers imply pistons are unsuitable for salt and or dirty water diving and that they are prone to failure in such conditions. I have never experienced or witnessed a piston failure at any time/anywhere while diving.


I did some research diving in college. Our dives were often in muddy tidal guts or in the surf where mud and sand got into everything. In some cases, we were roughing it without a good source of water for rinsing for up to a week at a time. I never experienced a failure or a problem, although I did make sure that my gear was thoroughly rinsed as soon as I had a source of fresh water available. I usually had everything checked after a trip like that, as well.

These days, I often go offshore for 3 or 4 days at a time, again with no source of freshwater to rinse my gear. I leave the whole schmeil mounted up on the bench, only removing the first stage to refill the tank in place.

While I keep my cameras and gear wet with saltwater soaked towels when I can, even then the gear often gets "dry".

On my annuals I always ask about any noted problems, particularly regarding corrosion or etching on the piston. I have been told my piston on the Delta looks as good as it did when I purchased the rig in 1985 (or 86? Duh. I'm getting old).

.

 

[oxyhacker]

The G250HP is basically the old G250 redesigned so it uses the newer S600 valve asembly. You'd assume there'd be some be a good performance boost to justify the change, but no one seems to be very excited about it. The newer SP designs seem to all be a bit more complicated than they need to be, which would be OK if it was the only way to get higher performance, but Atomic seems to be able to get as good or better with simpler designs.

Though Scubapro dealers tend to be very conservative for some reason, and often like to badmouth the latest gear. the one who said the G250HP wasn't as good as the G250 was probably telling anyone who would listen that the G250 wasn't as good as the old metal 109, not too long ago

Originally posted by DivingDoc
Oh -- theres a difference? What's the difference?

 

[mddolson]

Thanks for the reply Ricky,

Just for the record I have a Scubapro Mk4 along with the Mr12's I'm still using.

Mike D

 

[pt40fathoms]

When talking about the pros and cons of ballanced diaphram vs ballanced piston, one has to take into account the environment in which the regulator will be used. To be more specific, the temperatures under which it is to be operated in, both above and below the water.

If we are talking cold water temps, where the water is frozen at the surface, and 3c below, a balanced diaphram is the only choice. A ballanced diaphram is far less likely to free flow under cold conditions. This holds true for deep dives in salt water where the temperature can reach 2c. I'm not saying impossible, just less likely. I have seen ballanced diaphram regs go free flow at depth, and in some case, it has be "tweeked" to peek performance by someone who has just enough knowledge to get themselves into trouble. In other cases, it has been the new lighter and cheaper plastic ones

If we are talking diving in the warmer places on this planet, then this argument does not hold water (pun intended).

It is for this reason that the Mares Abyys is the most popular in these parts. Some other reasons for it's popularity besides being good in the cold is because it's smooth, and cheaper than it's next nearest rival made by Scuba Pro. Scuba Pro is a great reg, but we have seen too many free flow under the ice, so use it in the warmer climates and your OK. If Scuba Pro would do some R & D and fix this one little problem, I'm sure many people would buy their regs, even with the higher price tag.

As for the rest of the argument re: salt, dirt, corrosion. In my opinion, it's just sales hype.

 

[DivingDoc]

Originally posted by pt40fathoms


If we are talking diving in the warmer places on this planet, then this argument does not hold water (pun intended).

I sort of make it a policy never to dive in places where I need more than a 3mm wetsuit.

It is for this reason that the Mares Abyys is the most popular in these parts. Some other reasons for it's popularity besides being good in the cold is because it's smooth, and cheaper than it's next nearest rival made by Scuba Pro. Scuba Pro is a great reg, but we have seen too many free flow under the ice, so use it in the warmer climates and your OK. If Scuba Pro would do some R & D and fix this one little problem, I'm sure many people would buy their regs, even with the higher price tag.

The MK25 has something called a thermal insulating system. Does that make a difference?

 

[metridium]

Originally posted by DivingDoc
I sort of make it a policy never to dive in places where I need more than a 3mm wetsuit.

Wimp.

 

[DivingDoc]

Originally posted by metridium

Wimp.

Yep -- that's me. Diving's a hobby, not an occupation, so why shoud I dive in places where I'm not nice and warm.

 

[oxyhacker]

Can't agree. The old Scubapros like the 5 and the 10, with the SPEC (environmental sealing) kit, which fills the spring chamber with silicone grease installed are about as freezepoof as any reg ever made - I always use an old Mk5 with the metal 1st for ice/really cold diving and have never had a freeze up.

Unfortunately, when the Mk20/25 came out, SP tried to find a way to do away with the silicone and went with a TIB (thermal insulating bushing) and such, which didn't work as well, and the regs got a reputation as being not as good in cold water as their predecessors. However, the 20/25s can be SPEC kitted just like the earlier models, and are equally freezeproof when they are.

Atomic also recommends packing with grease for very cold water but specifies using Christolube which really runs up the cost of servicing - kitting one reg will use up most of a $30 tube of the stuff.

Actually damn few cold water freeflows are caused by the 1st anyhow - they usually happen in the second stage so 1sts tend to get blamed often for the vices of their 2nds. But 1st stage freeze ups when they do happen can be nasty.

Originally posted by pt40fathoms
A ballanced diaphram is far less likely to free flow under cold conditions. This holds true for deep dives in salt water where the temperature can reach 2c.

 

[metridium]

Originally posted by DivingDoc


Yep -- that's me. Diving's a hobby, not an occupation, so why shoud I dive in places where I'm not nice and warm.

You shouldn't....

of course, I'm nice and warm in 45F water....

cheeks excluded.