Piston vs. Diaphragm

[paulwlee]

From what I hear, in seawater it's fine down to 40F.
I don't think it's an issue when diving salt water unless it's in the polar regions.

 

[DA Aquamaster]

It's pretty commonly stated that all diaphragm regs are 1) balanced and 2) environmentally sealed. Neither of those statements are totally correct.

Most but not all diaphragm designs are balanced and not all diaphragm regs are environmentally sealed to prevent contact of water with internal parts. Many of those that are use a silicone filled chamber that can leak silicone oil and turn the reg into a non environmentally sealed regs over the course of a season. In general, diaphragm designs are more complex and require more maintenence.

An unbalanced piston reg will have the high pressure air from the tank pressing against the high pressure seat whichis normally mounted on the base of the piston. So as tank pressure decreases, this assistance to open the seat decreases and less pressure is needed on the LP side of the piston to close the seat so the intermediate pressure falls slightly over the course of the dive. When used with a balanced second stage, this will be totally unnoticed by the diver. When used with an unbalanced first stage, it will mean a very slight increase in inhalation effort at very low tank pressures, which serves as a nice reminder that you are running low on air. Unablanced piston first stages tend to be small and compact, very simple, and very reliable.

A balanced piston design will have the hp air entering from the side and the tank pressure offers no assitance to move the piston or open the HP seat. Intermeditate pressure is very stabel and generally speaking size of the hole int he flow through piston stem can be larger and accomodate more air flow.

Freeze ups in cold water are not a problem with piston regs if an environmental kit is used and most incorporate the use of silicone grease in the ambient pressure chamber. This is bullet proof in terms of performance but has the same limitations as the silicone oil used in many diaphragm designs in that it can leak out. But unlike nearly all diaphragm designs, it is easily user replaceable with no dissasembly of the reg required.

Scubapro uses a non-silicone based thermal insulating kit on their piston regs and it works very well on their unbalanced MK 2. It is however less than perfect on their balanced high performance Mk 25 due to its extremely high flow rate and you need to be careful with it in water colder than 50 degrees.

 

[Lead_carrier]

DA Aquamaster once bubbled...
It's pretty commonly stated that all diaphragm regs are 1) balanced and 2) environmentally sealed. Neither of those statements are totally correct.

Most but not all diaphragm designs are balanced and not all diaphragm regs are environmentally sealed to prevent contact of water with internal parts. Many of those that are use a silicone filled chamber that can leak silicone oil and turn the reg into a non environmentally sealed regs over the course of a season. In general, diaphragm designs are more complex and require more maintenence.

.

I'm not familar with any of the diaphram regs that use silicone oil to enviromentally seal them. Could you give me a couple of examples please?
Thanks

 

[jcalexander]

I am looking to purchase a regulator and considering one of the higher end Aqualung or Scubapro models(Aqualung Legend and Scubapro MK25/s600. From what I have read on this board the performance characteristics are very similar.
The main concerns I have are cold water performance. Is Scubapros TIS system more or less effective against freeze up as a sealed diaphragm unit such as the legend? or are the differences negligible in say 45 degree water?
Also among these 2 setups which 2nd is easier to dissassemble underwater to correct a silt or debris problem? Thanks to all in advance for your advice.

 

[Diver0001]

jcalexander once bubbled...
I am looking to purchase a regulator and considering one of the higher end Aqualung or Scubapro models(Aqualung Legend and Scubapro MK25/s600. From what I have read on this board the performance characteristics are very similar.
The main concerns I have are cold water performance. Is Scubapros TIS system more or less effective against freeze up as a sealed diaphragm unit such as the legend? or are the differences negligible in say 45 degree water?
Also among these 2 setups which 2nd is easier to dissassemble underwater to correct a silt or debris problem? Thanks to all in advance for your advice.

From what I've seen/heard, both regulators are good for cold water.

My main regulator is a Legend LX supreme. Where I live we dive in water that gets right to the freezing point for a month or two each year and it hasn't frozen up on me yet.

A friend of mine has a number of (5 or 6) scubapro regulators including a couple of MK25's and he doesn't complain about freezing. he does, however, complain about IP creep.

In any case in 45 degree water I wouldn't worry at all about either of these regulators.

As for disassembly for debris under water, neither of them is easy. If you want a reg that you can take apart in a flash under water and still gives you good performance in cold conditions then you're looking for the Sherwood Maximus. My backup is one of these. It breathes wet and a little heavy compared to my Aqualung but it's dead easy to take apart under water and probably one of the most reliable regulators on the market.

R..