Why do piston regs cost more than diaphragm regs?

[wetb4igetinthewater]

But ScubaPro regs and Halcyon wings (and other gear) just look good, and everyone knows that looking good while diving is half the battle.

Rule #6!

 

[Belzelbub]

The fact is when it comes to first stages, if the reg is properly serviced/tuned, no one is going to make the difference, though there are self-appointed experts who will claim they can feel the difference. Go and measure it, and compare the amount of force required to move the amount of gas that a person breaths during normal diving.

Exactly. As mentioned above, the record for a piston first stage may be that it flows enough air to support 135 divers. Even if a reg was half as good, it would be orders of magnitude more than what any human diver would ever need. At the most, I'd need to support 2 divers, and it would be while ascending for the most part.

 

[wetb4igetinthewater]

Exactly. As mentioned above, the record for a piston first stage may be that it flows enough air to support 135 divers. Even if a reg was half as good, it would be orders of magnitude more than what any human diver would ever need. At the most, I'd need to support 2 divers, and it would be while ascending for the most part.

We all have different priorities. While I prioritize consumers getting parts directly from the manufacturer (not working through a connection at a shop) and also get training for servicing is a huge plus for me. Others couldn't care less about either of those. From @rsingler's experiment, there is a difference in second stage design where some second stages perform better in certain conditions and worse in others. He actually did things I didn't even think about (such as while scootering).

 

[Eric Sedletzky]

The Scubapro Mk2 Unbalanced 1st stage is the most popular rental regulator because if you are a Scubapro dealer because 1. you get a great deal of parts when you buy them for your rental set, 2. They are so simple to rebuild, 3. The parts can take abuse for years and still work. Just to pipe in about the unbalanced piston first stage, the reason they are not popular outside of shallow water and swimming pools is the fact that when your pressure in your tank drops the performance (Intermediate pressure ) drops too. So going deeper makes you use more gas and the performance decreases faster.

How does an unbalanced reg make you use more gas?
You use what you use.
Besides that, if someone is diving deep enough when the tank gets low enough to begin feeling resistance (also using an unbalanced second stage) then they need to rethink their dive plan and gas supply choices. If you are breathing a tank down that low then you should be about finishing your dive and at your safety stop. For some people an unbalanced reg is a great idea; the ones that have trouble remembering to look at their air gauge.
Beyond that, all you have to do is pit a high quality pneumatically balanced second stage on an unbalanced 1st stage and it will breath all the way down to zero with little resistance.

 

[Baker_Dive]

The MK2 is my desert island reg. If I was stranded on a desert island the MK2 would be my choice.
In fact, if I didn’t get suckered into buying that MK20 by the hot shot salesman I probably would have bought the MK2 and been happy. But I can’t complain about the MK20, it’s been an excellent reg and going for 25 years now, no problems, no creep, perfect.
The only diaphragm reg I have is a Conshelf (actually two) and I can’t complain about them either.

What’s about second stage? What is a bulletproof secondlike the mk2?

 

[Eric Sedletzky]

What’s about second stage? What is a bulletproof secondlike the mk2?

R190 or an old metal 109…or an AL 1085

 

[CaptFran]

I’m curious why piston 1st stages cost more that diaphragm 1st stages?
If you look at Scubapro, their MK25, which is supposedly their flagship reg, is more expensive that any diaphragms they have.
Atomic has always been a premium piston reg with a premium price.
If you look at DGX regs, their Xtra balanced piston reg costs more that their diaphragm model, even though they are knock off brand of sorts with an internet presence and a right-to-repair business model.
I have not checked other brands because there are more brands that are diaphragm only and don’t offer a balanced piston design option.

This is confusing to me because pistons are simpler inside and have less parts. The only difference with a balanced and unbalanced piston reg is design. They are balanced by a design difference only (one moving part, the piston - two if you include the spring) and not by extra parts including a balancing chamber like with diaphragm regs.

Is it the machining and need for precision?
Or is it just because they can?

It's all about precision and machining. Just like all mechanical devices that use a cylinder and piston to produce compression or a balance pressure. Piston 1st stages also require good cleaning practices to insure that no foreign matter gets into the cylinder area. Yes Piston 1st stages are simple but require more care. Also keep in mind that piston 1st stages don't do well in ice diving conditions. Also keep in mind that 1st stagers delivery a specific pressure to the 2nd stage where the ease of breathing really comes into play. The 2nd stage is where many changes and improvements have been made over the past 4 decades with regulators.

 

[halocline]

the reason they are not popular outside of shallow water and swimming pools is the fact that when your pressure in your tank drops the performance (Intermediate pressure ) drops too. So going deeper makes you use more gas and the performance decreases faster.

That's not really accurate. IP does drop with tank pressure, but any significant increase in cracking pressure doesn't occur until tank pressure falls well below a point at which most divers will be at a safety stop or on the surface. I know this because I used one for years, routinely diving to 100ft or deeper with it.

And "going deeper makes you use more gas" has absolutely nothing to do with regulators. All divers use more gas at greater depth. That statement is a red herring.

I would also tell you that claiming that the MK2 is not popular 'outside of shallow water and swimming pools' is clearly wrong considering it is one of the best selling 1st stages in dive history, and has been relatively unchanged for decades. And there are many very successful copies, like Sherwood. Unbalanced flow-by piston 1st stages are very popular, period. They have been for decades.

The dive gear industry exists to sell divers new regulators, and the more expensive, the more money they make. You can't blame them, it's a business. But the fact remains that even the most basic regulators perform far better than is necessary to safely and enjoyably dive at recreational depths.

 

[lexvil]

That's not really accurate. IP does drop with tank pressure, but any significant increase in cracking pressure doesn't occur until tank pressure falls well below a point at which most divers will be at a safety stop or on the surface. I know this because I used one for years, routinely diving to 100ft or deeper with it.

And "going deeper makes you use more gas" has absolutely nothing to do with regulators. All divers use more gas at greater depth. That statement is a red herring.

I would also tell you that claiming that the MK2 is not popular 'outside of shallow water and swimming pools' is clearly wrong considering it is one of the best selling 1st stages in dive history, and has been relatively unchanged for decades. And there are many very successful copies, like Sherwood. Unbalanced flow-by piston 1st stages are very popular, period. They have been for decades.

The dive gear industry exists to sell divers new regulators, and the more expensive, the more money they make. You can't blame them, it's a business. But the fact remains that even the most basic regulators perform far better than is necessary to safely and enjoyably dive at recreational depths.

True, if there was ever a regulator that could take the place of the VW in the movie “sleeper” it would likely be the MK 2! if you bought a MK 2 and something like an s190 and did what 85% of all scuba divers do, dive a few dives a year and rinsed them well, made sure they were dry before storage and stayed off of scuba board you could probably go 20 years before either needed to be touched.

not that I would recommend that but in years past I’ve bought old lots of parts and usually there is a 40+ year old mk2 in the mix, I’ve never come across one the didn’t work.

 

[halocline]

I really wanted to initially buy a ScubaPro MK25 and then I saw a great video produced by RSingler that showed an MK25EVO used to provide air to 135 divers and I believe set a world record. If my memory is correct, RSingler mentioned that the MK19EVO and MK17EVO have very similar flow rates (less than 6.5% difference) and could service a similar number of divers.

The problem with that 'test' is that the tank valve is by far the weakest link in the supply chain. For a 1st stage to supply 100 2nd stages with air, you need a much higher flow supply than a single scuba tank, and in fact that's exactly what they use to measure flow rates. The MK25 has something like a maximum flow rate of over 200SCFM, which means theoretically emptying a AL80 in about 20 seconds. Obviously the tank itself can't keep up with that.

The only 'real world' application for flow rates is something tangential, which is IP recovery. A high quality 1st stage will allow IP to dip a minimal amount under demand, and recover very quickly. This is a little tricky to measure at home because IP gauges are not designed to measure pressure with air flowing. There's a venturi effect in the hoses and/or 1st stage whiich makes it appear that IP is dropping more while air is flowing. You'd need an actual flow meter to accurately measure the pressure drop.

Getting away from this boring and lengthy monologue, the short answer is that the MK19-17 don't have anywhere near the theoretical top flow rate of the MK25 but it has absolutely no real-world impact on how they perform diving.