Mistral freeflow

[veggiedog]

I restored a DW Mistral recently. Works great but starts to freeflow around 600psi tank pressure (estimated). Is this normal? If not, should it remain air tight all the way to an empty tank?

I dove 50' and used up a 72cf steel tank. No spg, no bottom timer (forgot it at home and no hp hose to connect my computer), but when I was done I used a pressure checker and the tank was at 450psi. Started to freeflow on ascent. In case anyone's worried, I had a backup pony.

P.S. Loved the experience but I was a bit too timid to bite down on my original mouthpiece (almost mint condition), so I held the mouthpiece in my mouth with my hand most of the time. I need to come up with a mouthpiece solution so I can start diving more regularly without concern for biting down (I like to bite my regulators, keeps em in my mouth)

[Bryan]

Shouldn't free flow no matter what the cylinder pressure is. Did you use a new spring? Did you resurface the HP seat ? Are you using the original 1st stage filter?
Give us some more details and perhaps we can solve it. Mistrals are very simple beasts and have few problems.

[veggiedog]

New HP seat, new filter, new spring. Lever adjusted to about 1/16 inch above the cover.

When restoring, I cleaned up the cone in the body with a 45 degree countersink, but just barely (by hand with light finger pressure). I can clean it up further but I was avoiding that to see if the seat held, and it did until tank pressure dropped. The original surface was a tad rough, but some of that was where the original seat had adhered to the cone leaving some of the nylon from the seat on the cone and consequently ruining the seat.

Do you recommend that I face the new HP seat? Or should I work on the cone more. If I work on the cone, I can clean it flat or I can put a new edge on it with a countersink (fits in the bore of the body very closely and is self centering). Seems that an edge is more appropriate, but that will enlarge the hole slightly near the top of the cone but still easily make contact with the seat. Visually, the cone is pretty clean.

I cleaned everything in a sonic cleaner and the metal surfaces appear almost new (they were already pretty clean).

[veggiedog]

I worked on the cone a little more and the seat is sealing now (knowing that they should seal at any tank pressure was helpful). I simply sanded the edge of the cone smooth with double sided tape, 400 grit wet sandpaper, and a wooden dowel. It took a while as the edge of the cone was rougher than I realized (sanding showed just how rough).

Does anyone ever refinish the cones with a cutter to restore the edge?

Having rebuilt and dove conshelf's for 25 years, the simplicity of the design of the DW Mistrals is artistic. While diving, I revelled in the simplicity of the single stage mechanism knowing how it was working from a mechanical perspective. I had no difficulty breathing off of the unit or clearing the lines: control of the vertical position of the mouthpiece relative to the first stage quickly became an automatic reaction governed by breathing resistance. The sound of the duckbill reminded me of my harley and was equally endearing. Truly a vintage gear head's dream (like the simplistic beauty of a flat head ford).

Thanks for your help.

[Bryan]

Glad to hear you got the free flow stopped.

[captain]

I would not use a cutter. Sanding with 400 grit paper is my preferred method. Sand no more than needed to take any nicks out. You don't want it too wide and flat. You can also finish it off by laping with 1200 laping compound in the same way valves in an engine are laped. I use a magnafying glass while sanding to be sure I don't cut too little or too much.

[veggiedog]

I was able to sand out the nicks this time but the edge is getting fatter. In fact, I left the last nick after I got a complete circle for an edge (i.e. the sealing surface is slightly narrower where the last nick is still partially there) because I didn't want to go too far and end up with a really wide edge. I was contemplating the future and the benefits to being able to cut a new narrow edge by reducing the diameter of the cone while maintaining the angle via the use of an angled cutter (opposite of a countersink (external instead of internal)) centered on the cone. This would remove the remnants of the last nick without lowering the height of the cone while also reducing the width of the edge. I also used a magnifying glass while resurfacing my cone.

However, I suspect that if I take good care of the regulator, the cone edge will probably remain intact especially since it is slightly wider and probably more robust as a result. I have never resurfaced the cones on any of my other modern regulators (seven conshelf xiv's), so they all have very sharp edges compared to the sanded cone in my Mistral (it does seal though).

Thanks for the quick responses.

[Nemrod]

Mine does not free flow either at any pressure. I love diving my old Mistral. I have had it for so long using it brings back memories. It is noiser than a Royal or DA but that is part of the charm. And they do breath very nicely. My unit has never had the cone sanded or resurfaced and thanks to Bryan I now have a NEW spare seat. This should keep my Mistral going another 45 plus years.
Me and Chucko down in Catfish Hole were well over 100 feet on Mistrals. The contrast between us and the group of Techie divers with quadruple everything and BCs and hardrives on their wrist was HUGE and both we and they took note.
James

[captain]

If it is not free flowing I would leave it alone for the time being.

[veggiedog]

I'm probably a techie too, but I go way back. I recently (last year) started diving again after a 12 year hiatus (college and kids), and I upgraded my gear while I was at it. I have always dove solo (started in '79), in the past it was with a 72cf and j-valve, healthways scubair 300 regulator (upgraded to conshelf xiv in '82), 70's style stab, no redundant anything. Now I use a manifolded double with a pony (three complete regulators), air integrated dive computer, bp/w. Still mostly minimal, but I have fully redundant systems (mask, gauges, lights, knives,floatation,...). Diving that way is very non-stressfull (except for lugging all that gear to my boat at the marina which involves about a 40' foot staircase drop from parking lot to dock).

I still enjoy the old way though. However, I do cheat, and I probably will continue to cheat as long as I dive solo, by lugging along a pony. I will be playing at depth soon, good to hear I can expect good performance out of my Mistral (I expected as much given the god of diving, Jacque Cousteau, used em ;>). I originally had a double hose back in '79, but I couldn't find parts (LDS convinced me that I MUST upgrade to a single hose because the double hose was dangerous and they didn't sell parts for it anymore...no internet to dispute his claims either.. probably not too bad a thing though). Finally having a working double hose sortof fulfills my dreams long ago of getting that double hose to work (I grew up watching SeaHunt). I'll be working up to no BC vintage diving soon.

I'll still be doing it the new way too (my 12 year old son just got certified, so I'll be trying out the buddy thing as well).

[Nemrod]

"Now I use a manifolded double with a pony (three complete regulators), air integrated dive computer, bp/w. Still mostly minimal, but I have fully redundant systems (mask, gauges, lights, knives,floatation,...). Diving that way is very non-stressfull (except for lugging all that gear to my boat at the marina which involves about a 40' foot staircase drop from parking lot to dock). "

Is this your open water rig or cave rig? What I have read from the DIR/HOG gurus (Bill Main)is that a aluminum single 80 is DIR for salt water/open water diving? You been hanging around with the evil PadI divers to long, you don't need any of that junk, come back into the sunshine and bask in the simple glory of vintage diving. Minimal and non stressful the above quote does not describe, lol. Just messing with you.

James

[BROXTON CHUCK]

Remember what I said about " TINKERITIS" The more you mess with it, the less it will work right. Set it by the book. They knew what they were doing in the first place. Captain NEMO never would have screwed with his regulators like that. The squid did, and look what happened to him!!