Da Aquamaster and 3000 PSI

[Paladin]

I learned to dive using a US Divers Aqualung DA Aquamaster back in the '60s. I sold the AM years ago and regretted it. I have just ordered one from Vintage Double Hose and am eagerly awaiting its arrival. My question is this: Can a DA Aquamaster handle 3000 PSI? I have a steel 72 with a J valve but I would like to use my AL80, too. Also, I want to put together a set of AL80 twins and want to use the AM with that rig.

 

[Luis H]

Can it handle it? Yes.

If you do a search, you will find that the Navy used the DA Aqua Master with 3000 psi aluminum non-magnetic cylinders for years… then again they had at the time an unlimited source of spare parts. In particular high pressure seats.

Will it hurt the HP seats? Well, probably not. It will put a bit more wear on it, but would it be significant? Well, I don’t believe there is a precise answer to that either.

You should also consider that with an unbalanced diaphragm first stage like the Aqua Master, the higher the tank pressure the harder they breathe. You will notice they breathe much better as the tank pressure goes down.

IMHO, you will probably be OK, but I personally prefer lower pressure tanks (steel 72) in general, but in particular with any double hose other than a RAM or a Phoenix RAM.

Have fun

 

[scubapro50]

I have several doublehoses (U.S. Divers Aquamaster and Dacor R4) and I never use them with 3000 psi tanks. I always vent the pressure using a singlehose regulator with a gague down to 2200psi. I have spent a lot of money to restore this old regs to original specs and I don't risk damage by using high pressure fills. A good alum 80 at 2200psi still should give you 20 minutes at 60 feet ..... plenty of time to enjoy that vintage dive. (It also helps to have a good wrist computer to watch your time and depth so you don't get bent.) I really wouldn't push the dive envelope with an old doublehose like I would with my new Mares Abyss.

 

[Paladin]

I see. Okay, so I use my steel 72 when diving a single tank. I was planning on doing that anyway, as it has a J valve. When diving twin AL80s with the AM, I can just have them filled to 2500 PSI (about what a new 72 would hold), and fill them to 3000 PSI when using my Aquarius single hose. Unless I am mistaken, the AL80s should hold about 65 cu. ft. at 2500 PSI.

 

[Nemrod]

I run my DA Aqua Masters at 3,000 psi routinely. N

 

[scubapro50]

I run my DA Aqua Masters at 3,000 psi routinely. N

but how often to you have to rebuild them ?

 

[Nemrod]

but how often to you have to rebuild them ?

We have gone through all of this over and over for several years now, each to their own, nonetheless, many of us run 3,000 psi with the unbalanced two stage regs. The effects of 3,000 psi on the DA is exaggerated. I have several with original seats that are doing just fine on 3,000 psi. They are only at 3,000 psi for the first few breaths, within minutes you are into the "zone." That said, I am a RAM guy.

Most of these guys at SD are on single stage and DA type regs and we had 3,000 plus psi fills on 80s.

BTW, a bit off subject, but the DA was produced with at least two volcano orifice diameters. I have converted my remaining two operational DAs to the larger orifice. A third I have on the bench now is the original small orifice but it is likely to become a PRAM.

To the OP, what you need are twined Faber LP85s, the 7.0 inch diameter version. It is a stout 2,650 psi tank that can operate at any pressures up to 3,000 psi with an overfill.

N

 

[halocline]

I learned to dive using a US Divers Aqualung DA Aquamaster back in the '60s. I sold the AM years ago and regretted it. I have just ordered one from Vintage Double Hose and am eagerly awaiting its arrival. My question is this: Can a DA Aquamaster handle 3000 PSI? I have a steel 72 with a J valve but I would like to use my AL80, too. Also, I want to put together a set of AL80 twins and want to use the AM with that rig.

You might consider a set of 72s instead of AL80s. 72s make very nice doubles, they're neutral empty as opposed to the 8 lbs positive of the AL80 set, and they weigh considerably less on land. I have a USD center outlet manifold if you're interested.

The DA can handle 3000 PSI, and I'm still not sure why everyone seems to think that this would wear out the seats. IP keeps the seat closed, not tank pressure. If the IP is not creeping, the seat is closed with the same force as at lower tank pressure. In fact, the IP is lower at higher pressures due to the greater upstream force. There is a larger pressure gradient across the seat/orifice seal, but I don't see how that would cause premature wear to a relatively hard seat, and nobody has yet offered a plausible explanation that I've read.

It's true that the yoke is subject to more pressure and could theoretically wear more, but nobody seems to be reporting that the old yokes are failing.

It should work fine, but you would probably find eventually that you'd appreciate the better overall performance of the RAM or phoenix.

 

[Luis H]

The DA can handle 3000 PSI, and I'm still not sure why everyone seems to think that this would wear out the seats. IP keeps the seat closed, not tank pressure. If the IP is not creeping, the seat is closed with the same force as at lower tank pressure. In fact, the IP is lower at higher pressures due to the greater upstream force. There is a larger pressure gradient across the seat/orifice seal, but I don't see how that would cause premature wear to a relatively hard seat, and nobody has yet offered a plausible explanation that I've read.

You are correct in that the summation of forces on the Aqua Master seat at any tank is always about the same (the about could be very important).

The forces on the seat assembly are the:
(+) the force from the spring,
(+) the pneumatic tank pressure force (tank pressure times the area of the volcano orifice),
(-) the pneumatic IP force (IP pressure times the volcano orifice area),
(-) the force from the pin (being applied by the heavy diaphragm, see note), ,
(-) the compression force on the seat

The (+) and (-) are just my sign convention for the direction of the forces. The direction of all the forces mentioned never reverse. The pressure always pushes against the surface, and the same about the spring, the nylon seat, and the pin. The pin can only push from the diaphragm to the seat.

During equilibrium with the 1st stage valve closed all this forces will always add up to zero (since there is no acceleration). In other words the forces will balance each other out.

Two of this forces you know that they change proportional to tank pressure, the one that is not as obvious is the compression force on the seat.

Let me add that as you have notice and most anyone that have an Aqua Master can verify, the IP in a DA AM is not a hard locking IP without any possibility of creep. It often only creeps for a few psi and then it stops. That increase in pressure pushes the IP diaphragm a bit which in turns reduces the force on the pin. This allows a bit more force on the seat creating a better seal.

At high tank pressure there is a higher differential pressure from the tank pressure to the IP. If the volcano orifice and the seat are not perfect, this higher differential pressure will require a bit more seat compression force to create a good seal. IMO, this effect has been observed in many Aqua Masters.

IMO, the seat material in an Aqua Master has a lot to do with the required force to cause a good seal.

Is the higher seat compression significant… probably not, but it is impossible to tell since there are too many variables to determine longevity of any one particular seat.

The Aqua Master has a long history of working with 3000 psi and I would use it with that kind of pressure, but I personally prefer to use steel 72. I also prefer the Royal Aqua Masters anyway, so it is definitely not an issue for me.



Note: the HP diaphragms also experience its own set of forces:
(+) the pneumatic IP force (IP pressure times the diaphragm effective area),
(+) the force from the pin (being applied by the seat, equal an opposite the one mentioned above),
(-) heavy spring force,
(-) ambient pressure force (ambient pressure times the diaphragm effective area).
In my sign convention, forces pushing in the direction away from the valve continue to be positive (+).


I hope the explanation above makes sense.
BTW, adding actual numbers to the equation as described above is very easy. Some of the numbers (like effective diaphragm area and compressed spring force) may only be approximations, but it can give a good idea of the force magnitudes we are working with.



The Mistral is a somewhat different demand valve. The Mistral has also been used with 3000psi, but they definitely do not breathe as well. Seat wear is also an issue, maybe only a small issue, but in any case replacement seats are now available for the Mistral and they are an easy regulator to service.

 

[Nemrod]

The thing everybody seems to dismiss is that the thing does not operate at 3,000 psi but for a few breaths. Yes, there is accelerated wear, I suppose, but not for the duration of the dive but for only a few minutes of that dive. So, instead of lasting, oh, thirty years it lasts instead twenty, yawn.

N