La Spirotechnique Venturi issue!

[Bryan]

I was re-assembling a La Spirotechnique Royal Mistral and noticed that the venturi nozzle was a little shorter than the ones I have seen in the past. I didn’t think much about it as there are so many variables to this model regulator I just choked it up to a part change.
Everything was Cool and the Gang…..I put the diaphragm in, can top and band clamp ring on. Always Always use a hose when testing a regulator. Especially a single stage regulator! I took a few breathes through the hose and it was flowing air like a jet. This is the norm for these regulators so not much new there. I did notice that the sound in the cans was a bit different than normal. Something was just not right but I can’t really describe why I thought that. Anyhow I took a really deep quick breath and all hell broke loose…..Air starts flowing WFO, blows the hose off the can…THANK GOD I was using a hose and not breathing right off the can!
I got it shut down and was scratching my head…..Naturally I had to try it again(Because I have no sense) and the same thing happened!
I took a while and stared in the can and then got mine out and looked inside the can……Finally the light bulb went on…..The venture nozzle was shorter than the one in my Spiro. And when I took the shorter one out I could see that it was drilled out to a larger inside diameter. By doing this the balance of airflow and vacuum in the cans was thrown way out of balance and let the diaphragm collapse and hold the regulator in a uncontrollable free flow situation. I know we have discussed the difference between the Stream Air/Jet Air venture nozzle and the Mistral nozzle. Obviously Gagnan and the other Engineers at Spirotechnique/USD had some very solid reasons for configuring them the way they did…..Here is the lesson today chillen…..1. If you modify venturi nozzles on single stage regulators serious injury and or death can result. 2. Always use a hose when testing a regulator. 3. E-bay is full of other peoples F-ups……

[1969ivan1]

Did the can come to you washed in bathroom cleaner then?

[Mudhog]

Spose its part of a kit to convert it to a chest mount fed by a sepperate first stage?

How does it work when fed 160 psi air?

[Bryan]

Spose its part of a kit to convert it to a chest mount fed by a sepperate first stage?
How does it work when fed 160 psi air?

I don't really have the provisions here to convert cylinder mounted regulators to chest mounted regulators so I can't answer that....Besides it came as a yoke/cylinder configured regulator so I'm almost positive it was supposed to be that way.

[Mudhog]

Strange deal. Being plated makes me think some factory made it, instead of Bubba with his Uni-Mat.

[Bryan]

Strange deal. Being plated makes me think some factory made it, instead of Bubba with his Uni-Mat.

My fault, should have said this 1st....Luis caught it too. The nozzle in question went out to be re-chromed along with the other parts on the regulator. It looked similar to the other one in the pictures before I sent it out.....

[luis]

Strange deal. Being plated makes me think some factory made it, instead of Bubba with his Uni-Mat.

I exchange some emails earlier with Bryan where I asked that same question. Bryan had the nozzle and other parts re-chrome. He said there is unquestionable evidence that the drilling was not done at the factory.

Enlarging the venturi nozzle like that will create an imbalance like Bryan mentioned earlier.

It is not easy to design a good balance between the amount of venturi suction and back flow into the can. This designs are often reached by calibrating using a bit of trial an error. It is not hard to do if you have a lab like Emile Gagnon did. It is often difficult to do a precise calculation to predict the exact response.

[capn_tucker]

Wow, that is one big venturi hole! I would never dream of monkeying with a regulator's innards; if one of my regs needs work I just put it in a box and send it to Bryan..

[Bryan]

Thank you for sending them to me. Lord knows I can use the coin! I get a lot of E-mails saying I sure wish I knew how to do what you do to these regulators¡¨ My suggestion is always the same and it's the appropriate season for it so I'll repeat myself. Get yourself a Stream Air, Jet Air or a Mistral from E-bay, garage sale, friend etc for a winters project..Buy a service/rebuild kit and a USD repair manual. Take the time, learn and understand how all parts works together..Experiment with what works and what does not. Share ideas and questions on the forum with others. Take it to the pool and try it out. If you are lucky enough take it diving in open water. When you get it just how you think it is perfect, buy a silicone diaphragm and see how radically that changes the dynamic of the regulator performance! When the spring comes I'll be willing to bet you have a regulator that will stand tall with any others like it..And hopefully have you saying,Which one will I do next ???

[Nemrod]

As Bryan points out and I and others have before and it bears repeating, never ever put your mouth directly to the can and breath--it will quite possibly KILL YOU DEAD. This is especially true of the venturi assited single stage regulators. This has killed people and it will kill you. It will rip your lung open and embolise you. Death follows shortly afterward.

Also, all used and ebay regulators should be viewed with great skepticism as potentially ill modified until proven otherwise.

Nemrod

[JES]

As Bryan points out and I and others have before and it bears repeating, never ever put your mouth directly to the can and breath--it will quite possibly KILL YOU DEAD. This is especially true of the venturi assited single stage regulators. This has killed people and it will kill you. It will rip your lung open and embolise you. Death follows shortly afterward.

Also, all used and ebay regulators should be viewed with great skepticism as potentially ill modified until proven otherwise.

Nemrod

Words of great wisdom from two very respected Vintage Double Hose Divers.

Please heed their advice.

[capn_tucker]

Also, all used and ebay regulators should be viewed with great skepticism as potentially ill modified until proven otherwise.

Nemrod

Not one of my eBay regs was ready to use out of the box. If you think about it, probably 90% of eBay double hose regs have been sitting on a shelf in someone's attic, closet or basement for anywhere from 20 to 50 years.
One of my Polaris regs I got from a private individual, and which had been sitting on a shelf (literally!) since 1962 actually breathed half-way decent.
I tried it in a pool, but would never trust it on a deep dive (at least not until serviced).
Just assume any auction regulator will have dry-rotted rubber parts, weakened springs, and probably corrosion where you can't see it...