50 Fathom Downstream Nozzle Position

[SurfLung]

- Simonbeans told me about Voit 50 Fathom "Compensated" regulators with the "Downstream" mechanism... He said they often had the nozzle pointing in the wrong direction and that was why they got a reputation as a hard breather. It makes sense that suction from the intake would encourage and assist the venturi flow from the nozzle. - Here are photos of three different Regs with the nozzle pointing in the wrong direction:

(Above)50 Fathom Compensated VCR2 (left) and VCR5 (right)
Both nozzles are pointing almost directly away from the intake hose.

(Above)50 Fathom Compensated VCR2 with nozzle pointing at a 90 degree angle to the intake hose.
- Simonbeans, AntiqueDiver, and a couple of other guys said all they had to do to make these regulators breathe great was point the nozzle straight into the intake hose and install the new single stage diaphragm.

[SurfLung]

Oops! Here's Better Info...
- The VCR2 and VCR5 Downstream mechanism nozzle is the larger of the two holes (I think) shown in the pictures below. The top two regs (above) have the opposite side pin hole pointing toward the intake hose. The silver one (also above) has no holes pointing toward the intake nozzle. My understanding is that the big hole should be pointing out the intake nozzle in order the create a venturi flow.

- There's another hole right under the lever. I tested this reg on a tank and air comes out all three holes when you press the lever. Heaviest airflow comes out the big hole. The other two are probably to create some back pressure against the diaphragm to stop the venturi flow when you stop inhaling.
- The "Downstream" valve seats AGAINST the tank pressure, so that the tank pressure wants to open the valve. The higher the tank pressure, the easier it's supposed to be to breathe.
- "Upstream" valves like the Mistral seat WITH the tank pressure so that the tank pressure wants to keep the valve closed. In that case the lower the tank pressure the easier it is to breathe.
- But, a properly adjusted Mistral is a proven easy breather... Venturi flow going out the intake hose overcomes the tank pressure holding the seat closed. I've found my Mistral to be an easy breather regardless of whether a tank is full or near empty.
- On the other hand, the 50 Fathom Compensated (VCR2) was sold so heavily as the "easiest breathing" regulator at all depths, I have to believe they really thought it WAS. It's fascinating to me that it would have the exact opposite reputation. NOW, seeing how the main venturi port may have been pointing in the wrong direction most of the time, perhaps that reputation was not deserved. Like the Mistral, maybe it just needs to be properly adjusted? How well would a Mistral breathe if the venturi wasn't pointing out the intake hose?

[Bryan]

Like the Mistral, maybe it just needs to be properly adjusted? How well would a Mistral breathe if the venturi wasn't pointing out the intake hose?

Use the search feature using the words Mistral and Venturi. Lots of past information available. If you experiment I would caution you to go slowly. In the past I have worked on regulators with modified venturi nozzles and they are flat out dangerous! Venturi airflow is a very powerful thing....Read in detail the info in Basic Scuba on venturi flow. The reason they did not point the nozzle directly down the horn was to create a slight back pressure in the can. Fred Roberts explains much better! Without this small amount of back pressure the venturi CAN in some cases take over, pull the diaphragm down and run the airflow wide open....Good way to pop a lung...And until there is back pressure applied the airflow will not stop. So be careful while you experiment...I have heard of many nozzles pointed right down the horn with zero ill effects. From my experiments changing the position of the Mistral nozzle in it's original configuration gives no measurable increase in airflow or cracking effort..
Good topic for discussion

[SurfLung]

In the past I have worked on regulators with modified venturi nozzles and they are flat out dangerous! Venturi airflow is a very powerful thing....Read in detail the info in Basic Scuba on venturi flow. The reason they did not point the nozzle directly down the horn was to create a slight back pressure in the can. Fred Roberts explains much better!

- Thanks for the feedback, Bryan. I don't have that Basic Scuba book so I have to ask a few questions:
- When you say you worked on regs with modified nozzles that are dangerous, are you talking about the same thing I'm talking about... Repositioning the VCR2 mechanism so the big hole points out the intake tube. Or, are you talking about someone actually modifying the mechanism?
- And, is there a Voit service manual that gives an official recommendation on where the big hole should point? I looked on the VDH manuals but only found a diagram that looks like NO holes point out the intake nozzle.
- Finally, the downstream mechanism appears to be the only one that is unique to VOIT... Everything else was the same or similar to USD, right? This uniqueness is why this thing has captured my interest. BTW - I bought a really nice VCR2 from a fellow here in MN... A few chips in the exterior paint but, the insides are mint.

- PS... I just found and ordered a copy of Basic Scuba on Amazon.

[Bryan]

- Thanks for the feedback, Bryan. I don't have that Basic Scuba book

Anyone that is truly interested in understanding how double hose regulators work should have both editions. Fred Roberts was there when they were new and helped develop and test much of what he discusses in the book. The first edition is the most important but you should pick up the later edition as both books don't contain exactly the same information.

- When you say you worked on regs with modified nozzles that are dangerous, are you talking about the same thing I'm talking about... Repositioning the VCR2 mechanism so the big hole points out the intake tube. Or, are you talking about someone actually modifying the mechanism?
Experimenting is great, just be careful and be aware of the dangers.
- And, is there a Voit service manual that gives an official recommendation on where the big hole should point?
Not that I have ever seen.

[Greg Barlow]

I have serviced a fair number of downstream 50 Fathom regs for fellow collectors, and have developed a deep respect for the design. Properly adjusted, it is a fine performer when the cylinder pressure is above 1,000-1,200psi or so.

Using a silicone diaphragm from VDH or TSM, the cracking effort can often be adjusted to 1.0" while on a cylinder filled to approximately 2,200psi. I adjust the lever height so that the bottom edge of the distal end is level with the plane created by the edge of the can. You can see that the distal end of the lever has a slight downward bend. The bottom of that edge is what should be level with the top edge of the can. That setting works for the wide majority of regs.

I do recommend setting the large orifice toward the inhalation horn. To ensure that the valve assembly doesn't rotate out of alignment you can drill an additional indexing pin hole in the top can. I don't personally do that as I adjust the opening of the filter C-clip so that it orients directly down the center of the inhalation horn. That way, you can instantly identify the position. I only remove the pin on my own personal regs and those of dive buddies. My reason for doing so is for liability reasons.

Does this technique create a dramatic difference? I'm not for sure, but I do like the sound of that "whoosh" of air flowing during the inhalation.

With that said, I did make an air dive to 176ffw using a downstream mechanism installed in TSM faux Blue 50 Fathom cans. While I had noticeable narcosis, I did not find the breathing effort to be objectionable. I have made a number of dives between 90-130' and it has always performed well. IMO, I think it breathes as well as a DAM. It is much like a Mistral except in a reverse manner.. The Mistral breathes noticeably easier as cylinder pressure decreases, while the downstream Gagnan design breathes harder with decreasing pressure.

If making two dives on one cylinder, I use a downstream valve on the first dive, and an upstream on the second dive. That way, I reap the benefits of each design.

Greg Barlow

[SurfLung]

- Thanks so much for the help Greg. I printed out your entire post so I can have it handy on the bench when I work on this beautiful regulator. Your experience, techniques, and practical tips are invaluable to me.
- I've tested it on a 300 psi tank and then on a 2,000 psi tank and it sealed fine and breathed fine. So, I don't think I'm going to risk screwing up the high pressure seat by taking the mechanism apart.
- I'll use your trick with the C-Clip orientation to indicate the big orifice position... Then point that out the intake hose.
- I'll check and adjust the lever height if it needs it.
- Then, I think I'll just put new diaphragm, duckbill, gray hoses, gray mouthpiece, and mouthpiece valves on it. The hose clamps are: 3 Voit and 1 blank.
- I got some of the Duplicolor "Intense Pearl Blue" spray paint but on second thought, I ordered a touch-up kit instead. The original paint is very good and maybe just a little touch-up on the scratches is all she'll need.
- Thanks again - Eben

[Greg Barlow]

As long as the mechanism is not leaking, I suggest that you do not disassemble the unit. The chances of getting the hard and soft seats in the exact same orientation is very slim. What will most likely occur is an agonziing leak that can only be corrected by refacing the nylon seat. Even then, the downstream system can be frustrating to work with.

Examples of the downstream 50 Fathom that were built in 1959, did not contain the removable sleeve (DS449), nor the hard seat (DS448). They are more difficult to rebuild, and are more likely to develop a leak due to a lack of stabilization of the seat & disc assembly (DS433).

The valve assembly did not contain any O-rings, and used two Phenolic washers under the removable seat. The 1959 examples did not have the Phenolic washers. If you do disassemble the valve, then I highly suggest that you replace the washers with one of the nylon washers that is included in the VDH 50 Fathom rebuild kit. The kit contains two washers, one of which should be kept as a spare. The combined thickness of the two Phenolic washers is equal to one of the nylon versions.

Greg

[SurfLung]

Ready to Dive...

- Greg, I took all of your advice and it is working beautifully! I did not disassemble and disturb the seat. Just positioned the big orifice to point down the hose. Did the c-clip trick so I can confirm the orifice direction. Checked the lever... It was already set the way you advised. Installed a new Voit gray silicone diaphragm from The Scuba Museum. New Duckbill... Blew some Talc into the duckbill like Basic Scuba sugggests. Installed new gray hoses, mouthpiece, and wagon wheel valves.
- I hooked it up to 300 psi and it breathes fine... Hooked it up to 2000 psi and I could hear a slight hissing leak. It breathed great, though. Hooked it to another tank I thought was 2,000 psi and the leak stopped. The tank was 2250 psi and the reg breathed great at that pressure, too.
- After reading in Basic Scuba how a tank with too high of pressure might cause the Downstream seat to leak, I tried it on a 2700 psi tank. Gently turned on the valve and it sealed fine. Test breathed it and it breathed fine.
- Bryan, that Basic Scuba book is like an encyclopedia of regulators... Wow. The description of the functions and then the trouble shooting tips reveal an awful lot.
- I'm very pleased with this regulator. Thank you Greg and Bryan for all your help.
- PS... I just got it to free flow on that 2700 psi tank... Geez! It stops immediately with resistance. I did it a couple more times. A quick breath as you take your mouth away can get it going but it stops by either thumbing over the mouthpiece hole or breathing against it. Just like when a DH mouthpiece is above the can in the water.
- PPSS I just got it to free flow with a 2250 PSI tank, too. Just a quick breath as you take your mouth away gets it going.
- PPPSSS I just did the same thing with my super tuned Phoenix HPR... Cripes, is this 50 Fathom breathing as easy as my Phoenix!??
-- Final PS I got it to free flow on a 1000 psi tank, too. You have to TRY to get it to free flow and you can't do it if you keep the mouthpiecce in your mouth.. Otherwise it just breathes normally and easily.

[SurfLung]

- This morning I put my 50 Fathom on the 300 psi tank to see if I could induce free flow. I certainly could! A quick kiss while pulling away from the mouthpiece and that starts it. The slightest back pressure stops it. It doesn't seem to be a problem whether I breathe fast or slow while keeping the mouthpiece in my mouth.
- The 1960 Voit catalog pitched this regulator as, "The easiest breathing, safest, simplest demand regulator ever built...". I have to agree this one seems to breathe super easy at least above 1000 psi tank pressure... And not bad at all down to 300 psi.

[Greg Barlow]

When I rebuild a downstream 50 Fathom, I perform what I consider to be the "ultimate" test of determining if the reg is leak free. I sit in front of the TV for at least 15 minutes, and physically work the diaphragm lever between 40-60 times per minute. This allows the nylon soft seat to establish a seating groove.

Next, I place the valve assembly on a cylinder pressurized to 2,200-2,300psi and work the lever a dozen or so times. I listen carefully for any audible leaks, and then turn off the cylinder valve. I press the lever and listen to the sound of the escaping air. Then, I open the valve and work the lever a few more times. The valve is closed again, and I leave it in that position for around 2-3 hours. Following that time lapse, I press the lever to release the trapped air. If little to no air escapes, I know that a leak is present. Generally, it is leak free. if not, then I reface the nylon seat. If the valve is still pressurized, then I apply cylinder pressure and then close the valve. I wait at least 12 hours, and again check for leakage. If the valve is leak free after 12 hours, it is dive worthy. An extreme test? Yes, it is. Just for my own interest, I once left one of my own 50 Fathom regs pressurized for a bit over 48 hours.... It was still leak free. That particular reg had been used on more than 50 dives since its last service.

Greg

[SurfLung]

- Thanks Greg... Once again all good, practical advice that makes sense. I'm not hearing any leaks but that idea to leave it pressurized after shutting off the tank valve and see if it still has pressure after awhile... I can see how that will definitely show any leakage.

[Bryan]

When I rebuild a downstream 50 Fathom, I perform what I consider to be the "ultimate" test of determining if the reg is leak free. I sit in front of the TV for at least 15 minutes, and physically work the diaphragm lever between 40-60 times per minute. This allows the nylon soft seat to establish a seating groove.

Next, I place the valve assembly on a cylinder pressurized to 2,200-2,300psi and work the lever a dozen or so times. I listen carefully for any audible leaks, and then turn off the cylinder valve. I press the lever and listen to the sound of the escaping air. Then, I open the valve and work the lever a few more times. The valve is closed again, and I leave it in that position for around 2-3 hours. Following that time lapse, I press the lever to release the trapped air. If little to no air escapes, I know that a leak is present. Generally, it is leak free. if not, then I reface the nylon seat. If the valve is still pressurized, then I apply cylinder pressure and then close the valve. I wait at least 12 hours, and again check for leakage. If the valve is leak free after 12 hours, it is dive worthy. An extreme test? Yes, it is. Just for my own interest, I once left one of my own 50 Fathom regs pressurized for a bit over 48 hours.... It was still leak free. That particular reg had been used on more than 50 dives since its last service.

Greg

Excellent advice from Greg as usual.....He uses the manual version of the machine I use on all the regulators I service.
Quick Set

Some good review for anyone working on regulators is
Regulator Hard and Soft seating 101

[SurfLung]

- I finally got to dive this 50 Fathom on Saturday. Connected to my USD Twin 38s at 1800 psi. I dove for 50 minutes in the lake at depths from 12-30 feet... Average 16 feet. (Great lake dive BTW... Visibility was 15-20 feet).
- Ease of breathing was excellent for the entire dive. I had 750 psi left in the tanks when I came out of the water.
- My Voit VCR2 50 Fathom seemed to work just as well as my Mistrals and DA Aqua Masters. I'm very happy with it.

[SurfLung]

Dive #2 - Here's a Photo...
Note the Beautiful Blue Regulator!

- Right after this photo, I got into a school of carp that totally wrecked the visibility for the rest of the dive.
- To compensate for short visibility in lakes, I've set my GoPro on r3 for the widest field of view (170 degrees) and you can see I'm getting a little of the vignetting in the corners of the frame... Even though I have a flat lens conversion on my GoPro housing. The r5 setting doesn't do this but is not as wide a field of view (127 degrees).