Test Dive with Mistral DH.

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CT-Rich

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Took my vintage Mistral double hose regulator for a spin at Ft Wetherill on Sunday. 18 lbs of weight was just about perfect weight with my 5mm Henderson suit. She breathed a bit harder than I expected, but for a 61 year old single stage regulator it went pretty well. I was in the water for 24 minutes, max depth was 25’. I didn’t breath down the tank far enough to need the J-valve, leaving the water with 750 psi. Ross, who was my buddy on the dive had trouble keeping up. With just a tank, mask and fins, you can move around pretty freely.
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You should mount your tank lower on the harness. The regulator should be between your shoulder blades, not your neck. That will make it breathe much better.
It is possible you have a very old model of Mistral where the venturi assist was still in development. If you feel like opening the can, or taking off the inhalation hose you can see if you have one of the very many good venturi ones. It will have a long venturi tube aiming directly out the middle of the inhalation horn.
I have found the Mistrals breathe much better than the two -stage DA Aqua Master.
One more tip. If you get tired of breathing effort, go upright in the water. Putting the can below the mouthpiece will result in positive pressure in your mouth making inhalation easier. It's also why you need the can between your shoulder blades, to make it closer to the depth of the mouthpiece when you're in normal trim.
 
One thing to try now that you have a low tank. Purge it until it hits about 300 PSI and test your J-valve. To be safe, do this above water, at home. Make sure that the j-valve works. Breathing should be noticeably more difficult with the j-valve up than down.
When I put together a j-valve I had to go through several valves to find a j-valve seat that wasn't cracked or degraded.
 
You should mount your tank lower on the harness. The regulator should be between your shoulder blades, not your neck. That will make it breathe much better.
It is possible you have a very old model of Mistral where the venturi assist was still in development. If you feel like opening the can, or taking off the inhalation hose you can see if you have one of the very many good venturi ones. It will have a long venturi tube aiming directly out the middle of the inhalation horn.
I have found the Mistrals breathe much better than the two -stage DA Aqua Master.
One more tip. If you get tired of breathing effort, go upright in the water. Putting the can below the mouthpiece will result in positive pressure in your mouth making inhalation easier. It's also why you need the can between your shoulder blades, to make it closer to the depth of the mouthpiece when you're in normal trim.

No you don't understand, he's almost 7 feet tall the laws of physics don't apply to divers that size.

Hey Rich glad to see you got that old goozer out there. If you could fine tune adjust that old gal I'm sure it would breath better. Did you notice it get easier to breath at 750psi? It should have.
 
I did play with body orientation quite a bit during the dive. A slightly head -up position improved the performance. It does have the Venturi assist on it.I did test the j-valve, it did show about 300 psi more in the down position than it did in the up (I also have few pieces of modern gear).

I will probably have to replace the webbing on the harness. It was pretty much maxed out, I didn’t have any more slack to wear the tank lower anyway.

Over all, my first impression was based on the way I normally dive, in a slightly head down orientation. As the dive progressed, I found the performance improving. Som of it may have been the tank running down or that I was getting more used to it an optimizing my orientation to get a it to improve.
 

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The lever height adjustment on single stage regs is citical. They will work OK improperly adjusted but there is a small sweet spot where the reg breaths markedly better. Tuning single stage regs is an art, finding that Goldielocks spot takes some time and experience. .
Also, did you replace the diaphragm? Reguardless of how it looks or feels, the old ones are no where near as good as the reproduction silicone ones.
 
Agree with @herman. I have spent hours trying to obtain proper lever height adjustment on Mistrals. It is more art than science. Once that goldilocks spot is found, WOB at lower tank pressures is literally effortless.
 
Agree with @herman. I have spent hours trying to obtain proper lever height adjustment on Mistrals. It is more art than science. Once that goldilocks spot is found, WOB at lower tank pressures is literally effortless.

I spent 2 afternoons and 2 test dives finding that sweet spot on my Jet Air but it was with worth it, that reg was almost as good a breather as my 2 stage USD.
 
https://www.shearwater.com/products/swift/

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