Piston verses Diaphragm

[Tod]

When I first started using a pony bottle set-up, I bought a low-end Aqualung Titan regulator for the back-up air source. The shop at the time sold me on the fact that they were using these regulators for their rental gear as they were sturdy and reliable units. (This was back in 2002.)

The Titan has a balanced diaphragm first stage. The second stage is a non-adjustable regualtor. All and all, the regulator was just fine and I didn't have much in the way of complaints until my second stage started to free flow all the time. I had it serviced and it still free-flowed (even worse). I took it back and they detuned it such that it has not been a problem since.

A couple of weeks ago I went to my LDS's 20-anniversary sale and they had a free raffle at the door when they opened. The first 40 people got a free ticket, after which we listened to the Scubapro representative give his lecture on how things work, which was rather informative. As it turned out, I was one of the lucky winners and won a new Scubapro Mk 2/R190 regulator! The Mk 2 has an unbalanced piston first stage and the second stage is also a non-adjustable regulator.

When I picked up the regulator, I told the shop owner that I was considering maybe switching the Scubapro regulator for the Aqualung for my pony bottle set-up. I asked him whether or not the Mk 2 Scubapro was a better regulator than my Aqualung Titan and he quickly said it was. I questioned the fact that the Scubapro was unbalanced and the Aqualung was balanced, but he quickly restated his answer without providing any reason.

Thus, I am wondering about the differences between the piston verses the diaphragm first stages? Is there that much of a difference that an unbalanced piston would be better than a balanced diaphragm? If so, why? Please educate me.

Meanwhile, I will note that it is not such a bad thing to have to contemplate whether or not my free regulator is as good as my other regulator. Either way, I still have a complete back-up unit I can toss into the save-a-dive case that I bring with me on my dive trips.

 

[Diver0001]

Have you tried it?

I don't know anything about the Scubapro regulator you mentioned but on the whole unbalanced piston 1st stages tend to decrease in performance with low tank pressures faster than balanced diaphram 1st stages do.

However, that's only one thing in a whole basket full of variables that determine how well a regulator breathes.

My advice would be to make a dive with both of them and do a "taste test" with them at various depths and tank pressures.

Having said that, there's a big part of me that wonders how a low-end scuba pro can be better than a Titan. If it does turn out to breathe easier maybe you can put the scubapro 2nd stage on the Titan first stage to make something better than either one..... Just a thought.

R..

 

[Chad Carney]

The Scubapro MK2/R190 is a classic unbalanced regulator that out preformed many balanced regulators in it's day. A review of Scubalab reports will prove this out, if you can still find them.

It would be a very good pony bottle regulator.

Regulators have progressed way beyond those days, but it would still be hard for a recreational diver to exceed those performance levels.

If you dive deeper than recreational depths you should be looking at current standards.

Chad

 

[redacted]

You just can't get much more bullet proof than a Mk2. No dynamic HP o-rings and only 3 orings total. But it shouldn't win too many ease of breathing contests. Drawback of an unbalanced piston is that IP will fall 10 to 15 psi as tank pressure falls from 3000 to 200 psi. This should not be a problem on a bailout bottle and some see it as an advantage.

 

[Mark Vlahos]

Either regulator should be just fine for your pony. By comparing the two regulators you are really looking at the old Ford vs. Chevy argument, with either able to take the role of the Ford or the Chevy. As has been stated the Mk2 will get a little harder to breathe at depths approaching recreational limits. Even if you take the regulator that deep and try to use it you may not even notice the difference and if you did you would probably not care. The Mk2 will also get a little harder to breathe from as your tank pressure gets low, again you may not notice the difference, but if you do it will serve as a nice warning that your tank pressure is getting dangerously low. Your Titan needed to be de-tuned to keep it from free flowing, this is fine, many octos are de-tuned in a similar manner and they still are ready for use should the need arise.

Be happy with either one. If it were me I would look at hose routing and other ergonomic considerations to decide which one I would use on the pony.

Mark Vlahos

 

[Tod]

Have you tried it?

I don't know anything about the Scubapro regulator you mentioned but on the whole unbalanced piston 1st stages tend to decrease in performance with low tank pressures faster than balanced diaphram 1st stages do. <snip>

Having said that, there's a big part of me that wonders how a low-end scuba pro can be better than a Titan. If it does turn out to breathe easier maybe you can put the scubapro 2nd stage on the Titan first stage to make something better than either one..... Just a thought.

I just picked it up yesterday so I haven't had a chance to try it yet. I plan to do my own comparison and see if there is much, if any, difference between the two.

My primary set-up is a Sherwood Maximus (balanced piston) and I have had no complaints at all with that one (after four years). I am familiar with the issues of balanced verses non-balanced after the tank pressure goes down. But I didn't think there was that much of a performance difference between the piston and diaphragm first stages, which is why I asked the question specific to the piston verses the diaphragm.

I was actually thinking about the same thing of mixing and matching the second stage of the new Scubapro with the Titan first stage. I wasn't sure if there was any issues that might keep them from working togeher (I can't think of any).

We'll see. If I can get out this weekend, mayble I'll report back and let folks know what I discovered.

Thanks everyone for the replies.

 

[ChrisA]

[I've used Titans and have one on my pony bottle. The thing is bomb proof but does not breath nearly as well as either my Apex or Oceanic Delta. But for a pony bottle "bomb proof" is what you want. The Titan breaths well enough at 100ft. but the apex is better

The titan is robust because the parts don't come in contact with saltwater. The Mk 2 is robust because it is so simple it can't fail. same result different route to getting there.

 

[halocline]

Actually, the unbalanced design has no impact whatsoever on the performance at depth. IP is always X above ambient pressure. At least that's my understanding. IP does fall as tank pressure decreases, but if the IP is set correctly (I think DA set my MK2 at 140PSI plus ambient) this is not noticable until the tank is WELL below 500psi, closer to 250psi in my case. At that tank pressure, if you're deep enough to require enough air to push the reg beyond it's capacity, you got way bigger problems than a decrease in regulator performance.

One reason, I think, that the MK2 breathes as well as it does is that the piston reacts very quickly and thus there is no "lag" time in holding IP when there's a draw on the regulator.

When I was looking for my first reg, it came down to the SPMK2 and the titan. I bought the MK2 after diving both, and I have no regrets. Give it a try.

 

[Diver0001]

I was actually thinking about the same thing of mixing and matching the second stage of the new Scubapro with the Titan first stage. I wasn't sure if there was any issues that might keep them from working togeher (I can't think of any).

The only issue you could theoretically encounter would be if the IP of the two 1st stages were differnt. That would require tuning but the Titan is easily tuned. Chances are good that it will work straight away. The LDS can double check that for you.

R..