Mistral Question

[Goodlifedivers]

Before I drive myself crazy trying to fix something that isn't broken, is a mistral is supposed to free flow at very low tank pressures?

Is there a general pressure that it should start to free flow? Like less than 500?

[kworkman]

It's supposed to breath easier at low tank pressure but I don't think free flow. Maybe the lever is to high? There are about 100 guys who can chime in with the right answer.

[Goodlifedivers]

That's what I'm trying to figure out. I may have the lever a bit too high. I have it set with the gauge from the store and then I fine tune it by checking to see if it free flows with the cans pressed together.

Everything seems fine but I had it on a tank with very low pressure (less than 400 psi) and it started free flowing. Just getting a consensus if it should free flow at all or should I bring down the lever

[luis]

It should not free flow.

It is very possible that the spring has lost some of its compression strength and is not pushing with the required force. When the tank pressure is high, the air pressure helps to seal, but when the tank pressure is low it is up to the spring force to seal.

If the lever is to high and just touching the diaphragm, that could also affect it. But in that case, it is more likely to free flow at any tank pressure.

[Ron]

I have had this happen by running a filter that was thinner than the original thickness one before. Bryan sells washers in the store if you use a thinner filter. I would guess that the thinner filter reduces the compression of the spring which, combined with low supply pressures may lead to a slight free flow.

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[captain]

Simple way to isolate the problem. If it doesn't free flow with the diaphragm removed then the lever is set too high.

[Goodlifedivers]

It only happens at very low tank pressures. It has a new spring and diaphragm in it.

I'll bring the lever down a touch more and see if that helps, it was breathing real nice though, maybe too nice.

[EHowe]

Mine does that too. I wouldn't say free flow but a slight leak at low tank pressures. Been diving it like that for a couple of years without a problem.

[Bronze06]

DITTO the Captain, Solanda and Luis.
It should not free flow period. Check filter thickness and if new add the washer that Bryan has. Take the front can off and put it on a low pressure tank (300-400 psi) as the Captain said. If it doesn't leak there, adjust the lever down a "skee tad" and assemble the front can and diaphragm back on the reg.
Have you replaced the seat?
Also, there might be a bit of verdigris on the orifice. I had the same problem as you on a few Mistrals and found that under high pressure the things sealed up just fine, but at low pressure (300 psi), the new seat would not seal due to a "tiny" bit of hard verdigris on the crown of the orifice. My cure was to GENTLY place a NEW #2 pencil eraser (attached to a pencil) down into the body ENSURING THE ERASER IS CENTERED ON TOP OF THE ORIFICE. Using light to moderate hand pressure, gently rotate it on top of the orifice first three turns clock wise and then three turns counter-clock wise. I then inspected the orifice to see if said verdigris was gone. If it is gone in one attempt, great, but stop there. There is no need to over do this. When finished the ERASER should have a small hole or depression in it's middle where it has turned into the center hole of the orifice. The eraser trick tends to ensure even abrasion on the crown. I have found that after performing the above procedure at most two to three times the verdigris or slight deformation is gone and after re-assembly the regulators sealed up like new.
Only do this if you see verdigris or suspect a "slight" deformation on the crown of the orifice and be very gentle so as to not damage the orifice by un-even cleaning pressure by the eraser. If the orifice has major corrosion of deformation/s on it crown, you will have to get a new body block. I have also used the same procedure on my "Stream Air" with great results. Just be gentle, yet firm and ensure the eraser is centered on top of the crown. I have rebuilt 10 Mistrals to date and all function flawlessly. The above procedure was used on 3 of them. I absolutely love Mistrals!

[Ron]

Hey Goodlife, have you made any headway on this?


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[Goodlifedivers]

Yes actually.

I ended up just lowering the lever a bit. I may have been too aggressive with it and it breathed great at lower pressures but once it got down to about 500 psi ish it would free flow. Lowering the lever a bit and checking it on a 200psi tank with the cans together creating pressure and it stopped free flowing. Still breathes fine but obviously not as easily.