Piston vs diaphragm... Balanced??

[captainhook426]

So I just realized I really have no clue what the difference is between the different types of regulators... I am particularly interested in cold water applications.. For instance a website that sells a certain manufacturers regulators makes a broad statement saying they do not recommend piston regulators to be used with cold water, or in "contaminated" water...but that specific manufacture says it's ok with the cold/environmentally sealed option installed... I don't really understand the difference... If anyone would like to un-dumb me that would be fantastic...



Oh and HOG... There the law has taken place.... I win!

 

[spectrum]

Balanced equates to a constant intermediate pressure over the range of cylinder pressure, good to the last breath.

Environmentally sealed applies to the first stage and means that water does not enter the workings of the regulator. If Ice forms it will be externally. Some are made this way, others can have a kit added.

Depth compensating means that the IP rises as you go deeper. Your second stage always gets air that is something like 140 PSI over ambient. Other wise tune/work of breathing gets thrown off as you go deeper.

Depth compensation is AFAIK a universal feature. In order to do so requires that water pressure act on the innards of the regulator. To allow this and be environmentally sealed some sort of membrane or other external feedback is needed. This is what the environmental "seal" provides. It may be a soft diaphragm containing an incompressible grease that relays the external pressure to the regulator or other means

With the exception of hardcore tropical divers environmentally sealed is the way to go. Due to adiabatic cooling as air is regulated "cold water" begins in the low 40F range so it's not just for extreme divers.

Pete

 

[captainhook426]

Is there any true differences between piston and diagram style first stages? What is the difference inhow thy regulate air pressures?

 

[spectrum]

Is there any true differences between piston and diagram style first stages? What is the difference in how thy regulate air pressures?

This will eventually evolve into a great debate but the answer is yes and no. They are based on different moving elements as the names suggest. Other than that it comes down to a spring resisting upstream pressure to equilibrate at the desired IP. Diaphragms designs are more amenable to sealing and thus have become more prevalent.

Pete

 

[herman]

Is there any true differences between piston and diagram style first stages? What is the difference inhow thy regulate air pressures?

While the end result is the same, there is a considerable difference in the design of the 2. You may find this helpful HowStuffWorks "Regulators and Scuba Breathing Apparatus"

While opinions differ, I personally do not like piston regs for cold water use, for warm water use, either is fine but still my presonal preference is a diaphgarm reg. While it is possible to seal a piston reg, the way it's accomplished (packing the spring chamber with some type of grease) is messy, waste lube and makes service a pita...since I do my own service I am not sure but odds are shops also charge a good bit more to service one....I know I would. To give you a little better idea of how it's done, look at the regs in the link above. The darker blue line in the diaphgarm reg is the diaphgarm, to seal one you basically add a second diaphgarm at the end of the reg (with a few other components inside) and now the area labeled water pressure is now an air space. Water pressure now presses on the outter diaphgarm which is mechanically linked to the inner (original) one.
The piston reg is sealed by filling the chamber labeled water pressure with a grease of some sort (silicone, christolube, ext). During service of an envoirmently sealed diaphgarm reg, it is simply dissambled, cleaned and reassmebled. It takes just a few minutes additional time to service a sealed diaphgarm reg removing and replacing the additional components. Servicing the piston reg, besides normal service work, the tech will have to remove the sealing grease, spend a lot more time cleaning the parts and during reassembly he must repack the chamber with grease, another messy job. Additinally some of the specified lubes are somewhat expensive which will also increase the price of the service....and that cost is not covered under part for life programs, the enviromental seals of most diaphgarm regs are.

 

[ams511]

Piston first stages are said to have a higher flow rate than diaphragm first stages, so in theory they are able to deliver more air. In practice, you will probably never notice the difference. Pistons regulators are also more tolerant to flooding. Sherwood firsts are pistons that use pressurized air to seal the first stage against contamination, so you do not need the lube.

 

[Nemrod]

The two classic heavy weight contenders that represent these two types of first stage are the USD/AL Conshelf and the Scubapro 109. The Conshelf uses a balanced diaphragm first stage with origins going back to the USD Royal Aqua Master double hose regulator (which in reality is a Conshelf with an integrated second stage). This first stage is ubiquitous and is found in current use by AL in the Titan and for that matter, the Legend. As well, it has been copied by Voit and then Mares. On the other hand, the famous 109 with Mark V balanced and flow through piston design is perhaps the darling of the classic single hose regulators. The Mark V is also probably the most cloned or copied first stage with copies being used by Tekna, Oceanic and others still to this day, including Scubapro in it's latest revision of the venerable design, is still there top of the line.

Piston first stages generally are capable of flowing more cfm than a diaphragm but it practical use it simply does not matter. Then there are failure modes, hmmm, not sure I am up to it right now, piston wins. Duckng and running.

N

 

[herman]

The "rest of the story" as an old news commentator use to say, on the flow issue is while the piston first stage may be capable of flowing more gas at full flow (wide open) it does not matter since the second stage is the limiting factor in the system so reguardless of which stage can flow more, the second stage can only pass so much and that valvue is less than either first stage. Plus, any second stage made in the last 30 years or so can flow way more gas than a diver can possibly breath. While on the subject, we should mention there are 2 types of piston regs. The flow through and the flow by. We have been discussing the flow through piston which is used on all mid to upper range piston regs. The flow by piston is an older design that is still used on lower end regs like the Scubapro MK-2 and almost all Sherwoods. It, on the other hand, will not flow as much gas as either of the 2 designs we are discussing but it is still a very solid reg that has it's place.

Not too sure I agree with you on the reliability Nem. While the piston does have fewer parts, the 2 critiacal orings in it are exposed to the enviroment. Poor operator maintiance can lead to salt crystals forming on those orings damaging them. Also, the working surfaces of both the piston stem and face are exposed to water, again poor operator maintance can cause issues. On the other hand all of the critical parts of the diaphgarm stage are internal and protected from the enviroment. As long as you don't get water into the reg I would go with the diaphgarm. Now allow a drop or 2 of salt water into the reg and I totally agree, the piston is likely to withstand that abuse better.
I think we can agree, with proper operator care, both are very reliable and both work well. There is a very good reason those 2 designs have been around for over 50 years and still going.


Balancing is a totally different subject that dive shops like to throw around to impress uneducated divers.
The goal of balancing either stage is to help keep the breathing effort of the reg the same during the entire dive. Both the first and second stages can be balanced but balancing just one of them has the same effect. As tank pressure changes, in an unbalanced first stage the pressure it delivers to the second stage (called IP) will change which will have an effect on how easy an unbalanced second stage will breath. While you can tell it, most divers would not notice it in a well tuned second stage. To prevent that change, the designer can balance EITHER the first stage or the second. If he choses the first, then the first stage design keeps the IP the same as tank pressure changes, the second stage gets a constant IP over the entire range of tank pressures so it's breathing effort does not change. On the other hand, the second stage can also be designed in such a way that it compensates for changes in IP, keeping the breathing effort the same as IP changes. The up side of balancing the second stage is you can also get a little better preformance out of the stage but like anything there is also a down side, the stage has more parts that can fail and increased cost. The typical sales model is a completely unbalanced is the low end, a balanced first with an unbalanced second stage is mid range and both first and second stage balanced are the high end regs.
Back to piston vs diaphgarm for a second, all modern diaphgarm first stage are balanced, only flow through piston stages are balanced, all flow bys are not....well make that almost all, Sherwoods are flow by and balanced...

 

[Fishpie]

One of the principal reasons I prefer diaphragm first stages is their ability to withstand severe abuse.
They are sealed by design therefore keeping the moving parts clean and dry.
Even if salt water does get inside and it gets stored for 10 years like that it doesn't matter if things get nasty and corroded as there are no o dynamic o rings that make contact with the reg body.

Another thing in their favor is simplicity to service.
It used to be said that the piston reg was simpler with fewer parts. This is no longer true. Something like a FST or Legend has fewer service parts and is easier to service than the current MK25.

 

[captainhook426]

Why do dive shops try to over compensate for this then? I'm really starting to just not like dive shops at all.