What makes a high performance diaphragm?

[Fishpie]

I typically see 2 different types of diaphragm 1st stages.
Barrel types such as the Conshelf/Titan/MR12
and
The T type (for want of a better description) such as Apeks/Legend/Zeagle/MR16,22/MK17

There are also 2 different HP seat shapes....flat and cone.

Leaving out the complexities of hose routing and cold water performance and strictly going on gas flow performance what features are needed for the ultimate diaphragm 1st stage?

What I think I know is that the T type has a more conducive inside shape for higher gas flow than the barrel type, and the cone seat probably lasts longer than the flat seat but ultimately doesn't make any difference to performance.

Another more specific question that I have.
Is the Apeks 1st stage "better" than a Legend 1st stage, and are they both "better" than the old SEA 1st stage?

 

[LeadTurn_SD]

Interesting question. All of my current regs have diaphragm 1st stages, but with variations in design (MR-22, MR-12, Zeagle Flathead VI). From a user's perspective, they all deliver plenty of air and a stable IP, so I can't tell any difference underwater.... I imagine any performance differences would need to be measured on a machine with the regs under high "stress" to bring out the differences.

I'm interested in what others think (I really don't know if either layout is "better").

Best wishes.

 

[herman]

Not sure if either is actually better, most likely some differences in max flow capability but in any case, way outside the usable range of any diver. The one thing you have to give the Conshelf/Titan/Legend and mother of them the Royal Aquamaster design, it has stood the test of time. Basically unchanged since 1965. I suppose the Royal Master is the grandmother of them all, its balance chamber design was a little different. Seat materials have changed and gotten better but design is still the same.
If you look closely at the Apeks design, it is still a flat seat, just the plastic material of the seat is thicker and tapered up, it still sits on an orifice and is opened with a push pin just like the USD design. Considering both designs work pretty much the same way I doubt there is any real difference in seat lifespan. Max flow is determined mostly by the HP orifice diameter in the reg but since most tanks can't flow as much are a reg is capable of, it's a mute point.
If I had to give either a "better" rating it would go to the Apeks design, not because of performance but IMO the design is a little more compact and has a better hose routing. Besides, reg performance is dictated by the second stage, the first stage has little to do with overall performance. In any case, both are tried and true designs.

 

[Fishpie]

....maybe IP drop and recovery should be the ultimate determination of 1st stage performance?

 

[Luis H]

I totally agree with Herman. The performance of “T” versus “barrel” design is going to be influenced by other factors not related to this geometry consideration.

I have opened plenty of Conshelf that have not being serviced in more than 20 or 25 years and before I opened them I always check IP and it has always been solid with no drift. I can’t ask for much more durability.

I get minimal IP drop from any of my Conshelf’s or my wife Titan’s (less than 10 psi) and the recovery is amazingly fast.

IMO one of the bigger advantages of the T geometry is that if it is well design it should be easier to assemble and therefore service the regulator. I have being servicing Conshelf (Royal Aqua Master) and similar regulators for almost 40 years and don’t have any issue assembling their first stage, but I do have all the special tools to assist the assembly. Special tools are not required, but it makes it much easier.

A well design "T" should be able to be assembled a lot easier since it is not held together by a snap ring.

Also not having to deal with the yoke (or DIN) to open the regulator every time could be helpful.


IMO, unless you service your own regulator, either geometry should work the same.
Servicing a Conshelf is actually very easy, but I can see the new T shape Titan being just a tad easier.



BTW Herman, talking about special tools… how is that tool we were talking about?
See you in a week.

 

[LeadTurn_SD]

....maybe IP drop and recovery should be the ultimate determination of 1st stage performance?

Maybe so. But with my regs, and a fairly decent IP gauge, I can't detect a measurable difference. Maybe on a good flow bench you could? Or again, maybe only on a full blown test machine. I think that if you can't see a difference on a standard IP gauge, then an average diver on a won't be able to tell the difference either.

Interesting topic; I wish I knew more about it, but I'm just a backyard mechanic, not an engineer, so it's over my head.

Best wishes.

 

[Akimbo]

....maybe IP drop and recovery should be the ultimate determination of 1st stage performance?

True, to a point. There are first stages with flow rates in the 80 CFM range. Do I really want a regulator that can empty a tank in a minute at the surface or 30 seconds at 33'?

 

[halocline]

True, to a point. There are first stages with flow rates in the 80 CFM range. Do I really want a regulator that can empty a tank in a minute at the surface or 30 seconds at 33'?

80SCFM is a pretty low flow rate for a first stage. The SP MK25 has a flow rate somewhere in the 300SCFM range. BTW it would not empty the tank any faster at depth than at the surface; actually it would be slower because the pressure gradient between supply and ambient would be a little lower. I know you're thinking that air we breathe lasts half as long 33ft; in that case, we're simply using twice the air for each breath so the regulator is supplying that, but it does not mean that the regulator is capable of supplying double the air that it can at the surface when fully open.

The tank valve is almost certainly the weak link in terms of flow rate. Regulator flow rates are tested with a much higher flow supply than a scuba tank, and with all the LP ports open. So if a reg has 4 LP ports, and tests at 80 SCFM, you can probably guess that each port has a roughly 20 SCFM capacity. (There are other variables)

Granted, flow rates in regulators have very little impact on real-world performance. IP drop as a performance indicator is much more realistic; but I know for a fact that it's difficult to measure IP drop accurately with a DIY-sort of IP gauge that attaches to a LP inflator hose.

 

[herman]

.............................
BTW Herman, talking about special tools… how is that tool we were talking about?
See you in a week.

Ran into a little snag...or maybe an overreaction on my part, I need to run it by you at SD. I will have samples. I am already packing.

 

[Akimbo]

... BTW it would not empty the tank any faster at depth than at the surface; actually it would be slower because the pressure gradient between supply and ambient would be a little lower. ...

Not true. Increased gas density and a reduced pressure differential of one atmosphere are inconsequential compared to doubling the volume. In fact, ambient flow rates can actually go up in some limited circumstances because the increased gas density sometimes reduces turbulent flow across seats and in hoses. One ambient cubic foot of gas at 33' is two cubic foot of gas on the surface. Ambient flow rates do not change dramatically even if you reduce gas density on HeO2 mixtures.

A saturation diver at 1000' at a normal 1.5 cubic foot/minute demand flow rate can suck down a 300 Bar/4,350 PSI 80 Ft³ bail-out bottle in under 45 seconds — of course you loose 30.7 Atmosphers/455 PSI due to ambient pressure.

BTW, you can’t get 300 ambient Ft³ of gas past a Scuba cylinder valve on the surface, let alone through a 1st stage regulator. Most regulator bench flow meters max out at 25 CFM. In reality, you are hard pressed to get 80 ambient Ft³ through a 3/8 IP hose with a 5.2 mm/.205" internal bore. A sustained 300 ambient CFM flow rate would empty an 80 Ft³ cylinder in 16 seconds.