Diapraghm or piston?

[PAPD]

Which do you prefer? and what advantages each has over the other?

 

[scubatoys]

Which do you prefer? and what advantages each has over the other?

Ford or Chevy??

Both get the job done... Pistons have less moving parts, easier to work on. Diaphragms are sealed from the environment by design, making them more popular for cold water, or really funky nasty diving conditions.

But keep in mind, just like the Ford or Chevy question, there is which one... If I asked would you rather have a Ford Pinto, or a Chevy Corvette... easier question... or Ford Explorer vs Chevy Vega...

Most diaphragm 1st stages don't have swivel capability, but some like the new Aeris Atmos Pro do... and a few others are incorporating swivels as well.

So really, I'd tell you look at the features you want in the entire reg set up - and don't sweat too much whether it is a piston or a diaphragm. There are good and bad regs in both designs.

 

[DA Aquamaster]

It's not correct to say that all diaphragm first stages are environmentally sealed. Many use a wet ambient chamber with little water flow and can be very susceptible to freezing up unless a separate environmental kit is purchased and installed. The environmental kit however then creates additional maintence issues as if the alcohol or silicone oil inside it leaks out, they are again very prone to freeze flows.

Some diaphragm regs use a very open ambient chamber and the increased water flow will keep them both clean and ice free. They offer 90% of the freeze protection with no increase in maintence and may be a better choice for most divers.

Unbalanced piston regs are super simple in design with on moving part and no dynamic o-rings exposed to HP air but their flow rates tend to be low and like an unbalanced diaphragm reg, IP changes with tank pressure.

Balanced piston regs usually offer more air flow and a shorter response time than a diaphragm reg and have a much lower parts count. They tend to be very reliable in service and are easy to service and maintain.

One approach to environmentally sealing a piston first stage uses a one way valve to seal the mabient chamber and a shrader valve to deliver intermediate pressure air to the ambient chamber. Another simpler apporach is to constantly bleed air into the ambient chamber.

Filling the ambient chamber with silicone grease (or more recently some type of O2 compatible substance) is also common and works well as long as the chamber is properly packed and the level of silicone is maintained with a boot.

Another approach is Scubapros TIS system which increases water flow and heat exchange in the ambient chamber while using someother design elements to prevent ice formation. This works very well on the Mk 2 PLus pisiton frst stage and also on the MK 16 diaphragm first stage but is not 100% reliable on the Mk 25 which still demands proper cold water technique to avoid a freeze flow.

Peronally, I prefer a balanced piston first stage due to the improved performance over most diaphragm designs, the relaibility and simplicity of the design, and the ease of maintainence.

 

[rescuediver009]

Peronally, I prefer a balanced piston first stage due to the improved performance over most diaphragm designs, the relaibility and simplicity of the design, and the ease of maintainence.

You mention nothing about overbalanced diaphragms and very little about dry sealed environmental chambers with a load transmitter. I would think that coupled with a balanced second stage and a load tranmitter that carries hydrostatic pressure is alot less maintenance and higher performance than a piston.

 

[IndigoBlue]

...
Peronally, I prefer a balanced piston first stage due to the improved performance over most diaphragm designs, the relaibility and simplicity of the design, and the ease of maintainence.

My view as well, exactly.

Piston regs are simpler in operation and more reliable in virtually all normal environments.

Ice diving or hazmat diving may be areas where a diaphram may be warranted. Since I do not dive in mud or in near- freezing water, there just is not any need for diaphrams.

 

[Zaphod]

The environmental kit however then creates additional maintence issues as if the alcohol or silicone oil inside it leaks out, they are again very prone to freeze flows.
...
Filling the ambient chamber with silicone grease (or more recently some type of O2 compatible substance) is also common and works well as long as the chamber is properly packed and the level of silicone is maintained with a boot.

How is it that a fluid-filled chamber in a diaphragm first causes maintenance issues, but it seems the same procedure in a piston first doesn't? They're both messy when overhauling them, but unless there's a breach on the outer diaphram, the user never sees the grease, etc. On the other hand, a grease filled piston first can and will ooze out creating a horrible mess.

Some diaphragm regs use a very open ambient chamber and the increased water flow will keep them both clean and ice free. They offer 90% of the freeze protection with no increase in maintence and may be a better choice for most divers.

Let's not forget about the popular dry sealed firsts....

like an unbalanced diaphragm reg, IP changes with tank pressure.

Funny, I thought virtually all current diaphragm regulators were balanced. You know, ones with a "balance chamber."

Balanced piston regs usually offer more air flow and a shorter response time than a diaphragm reg and have a much lower parts count.

Eh, just a minute. The moving part in a piston reg (the piston)is significantly heavier than the small seat in a diaphragm first. I don't agree that a balanced piston is more responsive than a diaphragm. It just doesn't make sense. Also, take a look at the parts count for a popular BP (the Mk25) and a popular diaphragm (TX100). It doesn't look like a much lower parts count to me. Including all dress-up parts and all o-rings, the TX100 lists 38 parts, the Mk25 lists 45 parts. Agreed, however a BP has a higher flow rate which most people don't need.

 

[BuoyantC]

Despite all the technical info, while breathing underwater there is no real noticable difference. Both styles are proven performers and there are many good regs on the market of either. Knowing that, I would just go with what works best for me where I live and dive, and leave the details to the designers.
D.C.C.

 

[rescuediver009]

How is it that a fluid-filled chamber in a diaphragm first causes maintenance issues,

simple. When taking it apart for overhaul it is important to make sure that the entire membrane is filled with silicone not air. the only awy to do this is to overfill it very slightly to ensure the ensure area is filled. I would agree that they are very very messy.

Funny, I thought virtually all current diaphragm regulators were balanced. You know, ones with a "balance chamber."

True, you win that one.

Eh, just a minute. The moving part in a piston reg (the piston)is significantly heavier than the small seat in a diaphragm first. I don't agree that a balanced piston is more responsive than a diaphragm. It just doesn't make sense.

If you take a look at the airflow in a flowthrough piston, they do allow more air because the more you draw that moreit gives vs. diaphragm, it only flexes that little bit to allow air passage. I would think that thisis a little different for over balanced diaphragms though. What do you think?

 

[Zaphod]

simple. When taking it apart for overhaul it is important to make sure that the entire membrane is filled with silicone not air. the only awy to do this is to overfill it very slightly to ensure the ensure area is filled. I would agree that they are very very messy.

Yeah, but my point is why would a fluid-filled diaphragm regulator be any more messy than a piston. Answer - it wouldn't. The original implication was that the diaphragm was more messy, so it was inferior in some way.

True, you win that one.

Actually, I won them all.....

If you take a look at the airflow in a flowthrough piston, they do allow more air because the more you draw that moreit gives vs. diaphragm, it only flexes that little bit to allow air passage. I would think that thisis a little different for over balanced diaphragms though. What do you think?

You're talking about air flow. I'm talking about responsivity. No doubt a flow-through piston will provide enough air for an elephant to breath, but for most divers that benefit is largely irrelevant.

 

[rescuediver009]

Yeah, but my point is why would a fluid-filled diaphragm regulator be any more messy than a piston. Answer - it wouldn't. The original implication was that the diaphragm was more messy, so it was inferior in some way. .

depends on what they are filled with. The silicone in the diaphragms is much more viscous than the cristo-lube in some pistons. Either way I think that we can agree that they both suck compared to the dry systems in apeks and aqualung.

You're talking about air flow. I'm talking about responsivity.

Yes. true