Piston.... Diaphragm... huh?

[NewDaScuba13]

So this was once, very blatantly, described to me. But, what is the real difference between a piston and diaphragm? Which one is better?

[CompuDude]

I was going to try to explain, and then I had a sudden bust of smarts.

http://en.wikipedia.org/wiki/Diving_regulator#Types

[mmakay]

I would add a couple of points to that wiki page.

1)
Pistons can provide larger volumes of air than diaphragms. This is not normally important or noticeable at recreational depths (as noted on wiki, it can be felt when very deep) but if you ever have the misfortune of needing to share air, you suddenly have two potentially panicked divers sucking hard from the same bottle. Piston 1st stages are better suited to for this. Whether that is significant enough to sway a purchase is up to you.

2)
I disagree with wiki's statement that diaphragms are "more responsive" and reduce breathing effort. That is almost entirely a function of the second stage, not the first. Some of the worlds easiest breathing regs are pistons. Atomic manufactures pistons exclusively and make some of, if not the best breathers out there.

[Blindref757]

So is a diaphragm better? Is it worth the extra money if you only dive in water above 55 degrees?

[CompuDude]

I don't think one is better than the other. My ScubaPro 1st stages (MK25) are piston, and one of the most popular regs with the most demanding of tech divers. The alternate reg, MK17, (better for water under 45 degrees) is also among the top regs chosen by tech divers, and it's piston, too.

[fire diver]

I didn't read the wiki page link. I won't give that site the benifit of my "hit" number.
<DIV></DIV>
<DIV>Anyway, as for performance, they are basically equal. Don't let the fact that a reg is piston or diaphram sway you in that route. Piston regs are generally considered to be easier to work on, but if you don't service your own gear, that's a moot point also. Now if it comes to dirty, of near freezing water, then the diaphram has an advantage. They can be enviromantally sealed, and provide you more protection. But 99% of divers don't fall into NEEDING that type of protection anyways.</DIV>
<DIV></DIV>
<DIV>So basically, buy what ever you want. </DIV>
<DIV></DIV>
<DIV>FD</DIV>

[cummings66]

I don't care for Wiki either, anybody can make it say whatever they want to so it's as accurate as revisionist history can make it. Junk pages IMO.
<DIV></DIV>
<DIV>As to needing the protection you speak of I'd say many of us do. Lake waters in MO and AR can be pretty dirty at times, my local lake has maybe 1 foot of vis on a good day and it's dirty as all get out. Silt, sand, all kinds of garbage in it. My buddies also dive year round, in fact Winter is the best time of year for diving.</DIV>
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<DIV>I'd agree that maybe 90% of the divers out there are fair weather divers, but I'd guess there's 10% of us that dive year round and in some real muck sometimes.</DIV>
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[Joew]

Originally Posted by CompuDude

The alternate reg, MK17, (better for water under 45 degrees) is also among the top regs chosen by tech divers, and it's piston, too.

Actually, the MK17 is a diaphragm 1st stage.

[CompuDude]

Originally Posted by Joew

Actually, the MK17 is a diaphragm 1st stage.

Oops. Senior moment. You're right, it's diaphragm.

[Joew]

Originally Posted by CompuDude

Oops. Senior moment. You're right, it's diaphragm.

I figured it was just a slip. I should add that your last post covered the topic pretty well. The MK25 and MK17 are both highly admired by tech divers. A high performance diaphragm OR piston reg will work for even the most demanding diver.