I've been working on another DH conversion for a while now. It has gone through some revisions and has required more custom machining than I wanted due to the changes. I thought maybe this would be entertaining for some of you while we are hunkered down. The whole sordid story is chronicled on another site, but I'm going to spare you lot from all the agonizing with this condensed version.
I have always thought that using a single hose first stage for a DH conversion would work pretty well. I ended up using a Conshelf VI first stage for a couple of reasons, but the main one is that I have several left over from my experiments with making a balanced single stage valve out of the Conshelf guts and a Healthways Scuba valve body. But that's another adventure.
There are several issues to deal with in this conversion:
A top can must be found and irrevocably modified.
There needs to be a way to connect the first stage body to the can.
There needs to be a remote second stage.
There needs to be a way to supply LP air to the second stage.
There needs to be a lever system that will work with a DH diaphragm.
There should be a way to multiply the Conshelf's single LP port.
I found an orphan Mistral top can that is fairly funky to cut up. To attach the 1st stage to the can, I machined the HP diaphragm retainer/IP adjuster and threaded it to accept a large retaining nut. It is installed with a rubber gasket like the Mistral valve.
IMG_4877 by Vancetp, on Flickr
I used a modded single hose second stage body that has an integral and adjustable LP hard seat/orifice out of an old Sportsways second stage. I also made a soft seat/lever retainer out of brass and made a stainless lever, much like my Dacor conversion uses. The idea was to supply LP air to the second stage via a short tube. I actually accomplished this, and it worked.
IMG_4898 by Vancetp, on Flickr
IMG_5181 by Vancetp, on Flickr
IMG_5192 by Vancetp, on Flickr
There are several reasons why I didn't like this much, mostly due to the difficulty in bending a brass tube in a sharp U bend and the kludgy look of the too long tube I came up with as a first attempt. I might have been able to get the short tube I wanted with a few tries, but I don't like the connectors either.
The next version is much cleaner.
[IMG_5287 by Vancetp, on Flickr
Because I had already cut the top can for the second stage, I had to make a longer through-bolt for the splitter. I also had to machine the second stage body.
I still need to do some fiddling, but it does work well. The proximity of the second stage jet to the intake horn makes for good venturi action, which will probably need to be tamed a bit.
IMG_5183 by Vancetp, on Flickr
No 50 Fathoms were harmed in this conversion! I only borrowed the bottom can for testing.