Voit 50 Fathom diving report

[Greg Barlow]

I had the opportunity to make three dives with my newly rebuilt 50 Fathom this weekend. Each dive was to approximately 55ffw, and the water temps varied from 62 degrees down to a low of 46 degrees.

When I rebuilt the reg, I chose to leave the valve assembly in the factory orientation with the small venturi hole pointed toward the inhalation port, rather than rotating it so that the large orifice was used (as some other divers have done). I will probably try that simple modification when the water warms a bit.

The reg performed very well. The air delivery was smooth, with no abnormalities noted. WOB is difficult to judge, but the reg seemed to breathe as effortlessly as my well tuned Mistral.

I did find out a few things about the 50 Fathom that I didn't know...First, the commonly seen schematics of the reg don't show that the valve body has a removable HP volcano orifice that is sealed by two gaskets. Basic Scuba identifies the reg as being adjusted by movement of the seat guide. This implies that the spring is compressed or relaxed to adjust how much tension is placed on the seat disk retainer. Logic would show this to be correct when you look at Roberts's illustration of the reg. Well, that isn't entirely accurate, and that may be what leads some techs to scratch their heads when working on the valve mechanism. If the guide is not torqued to a certain point, the orifice and two gaskets do not achieve a leak free seal. At first, I couldn't determine why I had a persistent leak at pressures from 500psi to 2,500psi. The leak didn't appear to get any worse with increasing pressure, which was a bit puzzling. I didn't have a factory repair manual for that reg, so I kept studying the information that Roberts had provided. I then disassembled the valve again, and looked at the seat with a bright light and magnification. I found that under the bushing (not illustrated in drawings), the removable seat had the two phenolic gaskets between the seat and valve body air inlet. I then realized that without adequate pressure on the bushing and seals the incoming air would leak before it ever got to the HP disk retainer assembly. I slowly started tightening the guide with an incoming pressure of 500psi until I had no leakage. I then increased the pressure to 2,500psi and found no further leakage.

This is a bit perplexing, as the information that Roberts included in his book doesn't identify this as a part of the design. If you went strictly with the drawing and description, then the guide's position would be solely responsible for the mechanical adjustment of inhalation resistance to the incoming air pressure. Roberts was Voit's chief engineer for several years, and one would think that all design features of the reg would have been included in his book.

A real neat feature of the Voit 50 Fathom, and the Polaris is the way that the way that the lever plate moves horizontaly to adjust for the primary and/or secondary lever height. IMO, this is superior to the system used by US Divers on the Mistral. On the Mistral the lever plate ends up getting bent if any tension is placed on the two screws that position it on the valve body. The large knurled adjusting wheel, and it attending hex nut are intended to anchor the plate in its adjusted position. The Voits use four 8-32 machine screws, along with inner toothed lock washers to maintain the plate.

My newly tuned 50 Fathom also features one of Bryan's silicone diaphragms. I have the diaphragm lever set just slightly above the rim of the top box, and I did not experience any free flow from too much tension on the valve.

All-in-all, a reg that I hope to use on many dives!


Greg Barlow

[1969ivan1]

That is great that you got that reg in the water. It is a testament tot he great members we have that the part was made available to you so fast.
I can't wait to use it at PORTAGE this summer.

Since you got my VOIT TRIESTE up and running, I guess I will let you dive it first.
Anyone out there know a good source of main diaphragms for the the trieste? I would like to locat an extra, just in case.

[Greg Barlow]

That was the first Trieste that I rebuilt; as the one I owned had never seen water, let alone a rebuild. Of course, the first stage is the same as a Titan II, and I have rebuilt several of those in days past. Voit had a really neat design with that model, as the LP and HP really extended the reg's capability...Can you say PHOENIX?

The Trieste uses the MR series of components in the 1st stage, so the HP valve is a Mares version. I also used Viton O-rings throughout, and one of Bryan's reproduction first stage diaphragms for the DA regs.

Rob's comment about the availability of diaphragms is a concern. It is significantly larger in diameter than the MR regs, including the Mares models. I wonder if anything in the commercial diving industry would fit the reg? Perhaps Bob3 might be able to find out. Some of the metal second stages on those units are pretty large in diameter.

Now, I want a decent complete Trieste that I can rebuild and use as a diver! Time for a posting in the "Wanted" section...


Greg