<non vintage>Mistral IP settings

[simonbeans]

Well, you were right about the two regs. I tried to keep that Aqualung Mistral in its box, but it had to show off in front of my friend. Next thing you know that Royal Mistral jumped off the shelf and kicked the living crap out of that Mistral. The Spirotechnique also grabbed my camera and forced me to take photos of it to show "who's boss". So, here is the little arrogant newcomer. I do know that now that it is king of my regs, it don't want to go home to "Daddy" aka missourireb.




Oh, by the way, the pressure gauge was my friend's who uses it to service regs for a competitor dive store. He checks it against 2 others regularly for accuracy. I will take the Mistral to my dive store this week and run it on the bench to be sure.
Allan

[standingup]

WOW
words fail

[Bryan]

Rarely do I part with a regulator and have seller’s remorse……Not the case with this one.

Sorry for getting off track…..Now back to talking about the FANTASTIC, Bionic new USD Mistral and it’s IP challenges.

[1969ivan1]

That is one sweet spiro that you have there Allan. I think it even looks better than mine! That chrome is so sweet. Bryan did a good job on that one and I love the late black label.
We can have spiro mistral wars at WEEKIE now.

[simonbeans]

Back to the Edsel of regulators. I took the never used, out of box Mistral to the dive store where I work and put it on the bench. The IP is set at 141 psi. My gauge at home is not quite that accurate, but the store's is right on. Looks like the quality control inspector was really asleep on this one.

[Sea Explorer]

Listen up Kids

I finally got to go through a mistral with an Aqualung Master Tech and here is what I learned:

The IP should be set at 135 to 140 as stated earlier. This may seem conservative but there is a reason. Aqualung environmentally sealed regs (including Mistral) are designed with a depth compensating IP. This means that at depth the IP increases up to 10psi.

You can see this for yourself on the bench. Attach your IP gauge to the Mistral now with the reg under pressure push on the silicone disc on the end of the Titan 1st stage. You will see the pressure on the gauge increase 10psi. If you tune the reg too high when the depth compensation kicks in you can get a free flow.

This being said the mistral with 1st stage set properly and the second stage lever adjusted properly performs very well.
I hope this info is helpful.
-Ryan

[Sea Explorer]

As an additional note:

The free flow at high IP is a particular concern depending on the octo you are using. Make sure it can handle the base IP + 10.

-Ryan

[luis]

I guess this is what they call their overbalanced first stage. Basically the outer ambient pressure diaphragm is a bit larger than the inside intermediate pressure diaphragm. I thought this was part of the Legend; I didn’t think the Titan 1st stage had this feature.

Personally I fill it is great for advertising, but nothing else. Apeks is big on this design.

The disadvantage is that you can’t fine tune the regulator for shallow water; it can only be fine tuned for deeper water. Their theory is that at deeper water is when you need it to have the highest performance since the air density is higher. Instead if you have a good first stage with a constant IP above ambient, you should be able to fine tune the regulator for all depth.

With a pneumatically balanced second stage, a changing IP is not very important. But, with a basic down stream valve like the one in the new Mistral it would be best (IMHO) for the IP to be constant (above ambient). A constant IP force can be adjusted to be balanced against the second stage spring force (minus the soft seat compression force).

IMHO, this is another reason were a good old RAM (or a new PRAM) is far superior to the new Mistral. The other big one is main diaphragm size.

[Sea Explorer]

The titan doesn't have the feature only the titan supreme. It is achieved with the environmental seal mechanism on the Aqualung cold water regs and all the Legends.

You can remove the environmental seal on the mistral and it will maintain the constant IP. It only takes a second to do. The over balanced feature is something different.

I found on my mistral that the second stage lever was not adjusted properly leading to increased cracking pressure. When tuned up performance was on par with my other well tuned regs. I plan to take it to the pool on Saturday & local diving hole for some deep water tests next week. I will report back.

-Ryan

[Sea Explorer]

Luis, it appears upon further research that you are correct about the depth compensating mechanism being called overbalanced. From what I can gather different manufactures use the term overbalanced to refer to different mechanisms. Although Apex/Aqualung use overbalanced to refer to the depth compensation I think depth compensation is a more accurate description in the context of balanced regs as we know them, balancing the output pressure regardless of input pressure. The terminology is confusing two different things.-Ryan

[luis]

“The titan doesn't have the feature only the titan supreme. It is achieved with the environmental seal mechanism on the Aqualung cold water regs and all the Legends.”

Yes, that is what I meant. I was thinking of the Titan Supreme with the outer environmental diaphragm.


“You can remove the environmental seal on the mistral and it will maintain the constant IP. It only takes a second to do. The over balanced feature is something different.”


I have heard different definitions from different companies for an over-balanced feature. In the case of Aqua Lug and Apeks I am fairly certain that the increasing IP as a function of depth (due to the differential diaphragm areas) is what the call over-balance.
Please explain if I am wrong.


I guess I took to long to answer.