US Divers Royal Mistral: chronicle of a death foretold

[stefeyme]

Hi everyone, this is my last post about USD Royal Mistral.

I hope you'll like it!

https://vintagescubadiving.com/us-diver ... -foretold/

Cheers!

US DIVERS ROYAL MISTRAL #1715 - 00137.jpg

US DIVERS ROYAL MISTRAL #1715 - 00133.jpg

US DIVERS ROYAL MISTRAL #1715 - 00113.jpg

[luis]

Very nice pictures. I can't wait to read the article.

I like the sub-title: Royal Mistral: another case of "Better is the Enemy of Good Enough"

Well actually it is going to have to wait, I am going diving.

[jrltenn]

Thank you. I enjoyed that article very much.

[antique diver]

Stephane, that was a very interesting and informative article. Nicely illustrated too. Thanks!

[ScubaLawyer]

Great write-up ! Thanks for preserving DH history. Mark

[Drado]

Great read! Thanks!

[swimjim]

Nice write up! Thank you for your efforts!

[luis]

Hi Stephane

The Sleeve
This spare part is meant to guide the poppet perfectly straight onto the disc of the retainer to provide sealing.

The purpose of the sleeve is to provide a mechanical support to the balancing chamber (not a guide). The balancing chamber has to be mechanically supported for it to work.

The pressure thrust (force) on the back surface of the balancing chamber has to be transferred to the structure. Otherwise, (if the balancing chamber was floating) the tank pressure “force” would press on the back of the seat through the spring.

If the sleeve was not there (if it was not installed) the regulator would seem to work OK, but it would not be balanced. The tank pressure would act on the back of the seat via the now floating balancing chamber and it would increase the spring force on the back of the seat.

The RAM, Conshelf, etc. doesn’t need this sleeve because the first stage body is machined with the same step (perimeter shelf) built right into the body. In essence the sleeve is just machined right into the body.

Mechanically locking the balancing chamber is extremely important if you want the regulator to be balanced.


BTW, the cone is self aligning. That conical seat will try to align itself into the orifice. Adding any kind of a guide to a conical seat can be very counterproductive. The guide would have to be perfectly concentric with the orifice. A conical seal like this cannot tolerate any misalignment.


Conical poppet seats like this one have been tried by Poseidon and Mares, with some success , or at least partial success. I used to service a lot of Poseidon Cyklon 300 first stages back in the 70’s and they were OK. Sometimes the seal was very reliable, but at times, I have had to replace a number of soft seals to get one to work.


The conical poppet on a soft orifice seat seems like a good idea, but in my experience, it is not very forgiving and therefore I found that it’s reliability is hard to reproduce, it is not consistent.

[stefeyme]

Hi Stephane

The Sleeve
This spare part is meant to guide the poppet perfectly straight onto the disc of the retainer to provide sealing.

The purpose of the sleeve is to provide a mechanical support to the balancing chamber (not a guide). The balancing chamber has to be mechanically supported for it to work.

The pressure thrust (force) on the back surface of the balancing chamber has to be transferred to the structure. Otherwise, (if the balancing chamber was floating) the tank pressure “force” would press on the back of the seat through the spring.

If the sleeve was not there (if it was not installed) the regulator would seem to work OK, but it would not be balanced. The tank pressure would act on the back of the seat via the now floating balancing chamber and it would increase the spring force on the back of the seat.

The RAM, Conshelf, etc. doesn’t need this sleeve because the first stage body is machined with the same step (perimeter shelf) built right into the body. In essence the sleeve is just machined right into the body.

Mechanically locking the balancing chamber is extremely important if you want the regulator to be balanced.


BTW, the cone is self aligning. That conical seat will try to align itself into the orifice. Adding any kind of a guide to a conical seat can be very counterproductive. The guide would have to be perfectly concentric with the orifice. A conical seal like this cannot tolerate any misalignment.


Conical poppet seats like this one have been tried by Poseidon and Mares, with some success , or at least partial success. I used to service a lot of Poseidon Cyklon 300 first stages back in the 70’s and they were OK. Sometimes the seal was very reliable, but at times, I have had to replace a number of soft seals to get one to work.


The conical poppet on a soft orifice seat seems like a good idea, but in my experience, it is not very forgiving and therefore I found that it’s reliability is hard to reproduce, it is not consistent.

Thanks Luis for your feedback! I really appreciate it. I'll change my post to reflect that.
Many thanks again
Cheers!