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Ron
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Voit little gem III

Wed Apr 02, 2014 4:39 pm

Apparently, during one of the 20 renames of Voit their engineers took a bunch of little gem II regulators, which were a piston first stage identical inside to an Aqualung Aquarius, took the crappy tilt-valve second stage off, added a lever action second stage, and called it a "little gem III" without changing the label. These regulators appear during the 1973-75 Voit/Swimaster/AMF/whatever catalogs. I rebuilt one a number of years ago for someone, and I found another one for a pittance so I bought it. The last one I worked on breathed way better than an aquarius, despite the mechanically identical first stage. It has a tiny second stage on it, so maybe that has something to do with it. I swear though, for an unbalanced piston regulator, it is one of the best breathing regulators that I have used.

Anyone know anything about the history of these short-lived regulators? They look like this:
$(KGrHqN,!psF!O+TOIMyBQS4gtly2g~~60_57.JPG
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antique diver
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Re: Voit little gem III

Wed Apr 02, 2014 6:15 pm

Was the diaphragm soft enough to use or did you find a modern substitute?
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Ron
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Re: Voit little gem III

Wed Apr 02, 2014 10:31 pm

The guy I purchased it from already had an MR-12 silicone one in it. I think the exhaust tee is new as well. It seems like a later model Mares one. Bill, you have messed with these before IIRC. Is yours a really good breather too?
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Re: Voit little gem III

Wed Apr 02, 2014 11:35 pm

I acquired one and went through it about 3 years ago. It surprised me how well it worked for being so small and simple, but I never took it diving. I guess I'll give it a try next time out. That exhaust tee looks like it came off an MR12-III... good to know those will fit. Also those diaphragms sure fit a lot of regs in the Voit line.
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Greg Barlow
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Re: Voit little gem III

Thu Apr 03, 2014 10:21 am

Ron,

The second stage is of the same design as that of the MR12, and it uses an effective venturi orifice. If the reg doesn't have a silicone exhaust valve installed, I suggest using one of the VDH 26mm versions.

The first stage does offer decent gas flow for an unbalanced piston. I typically adjust the first stage with stainless shims to 130-135 with a cylinder pressure of 2,500psi. As with all unbalanced piston designs, the IP will drop around 10-15psi as you get near reserve pressures. I adjust the second stage to a cracking effort of 1.25" at 2,000psi.

Earlier Little Gem versions used a much smaller exhaust valve, and an exhaust tee that was held on by two stainless steel machine screws. Their exhalation effort was noticeably higher.

As you mentioned, Voit was simply "using up parts" in the creation of the Little Gem III model. The rarest version of the design was that of the late 70s Swimaster Polaris II. It had 2 LP ports, while all of the earlier models had but a single LP port. It took me several years to locate one in great condition.

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Ron
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Re: Voit little gem III

Thu Apr 03, 2014 12:23 pm

Thanks Greg! I might post a little rebuild demo and list everything needed to do one given your guidance so that if anyone else on the Web wants to do one they can use it as a reference. I think Bryan carries everything for the rebuild.

As an aside, maybe one of you mechanical engineering types can answer this. Ceteris Paribus, if the case of a second stage regulator is smaller, does it deliver air via demand at a higher pressure or anything similar to that? I've noticed that it seems that tiny second stages really "give you a lo of air", but I know that is anecdotal. The USD micra, for example, seems to pack a punch. Is there any scientific reason for that?
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luis
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Re: Voit little gem III

Thu Apr 03, 2014 3:28 pm

What you are describing sounds like a strong venturi flow effect. That is normally caused (in a regulator) by the aerodynamic flow/ jet shooting air from the demand valve into the mouthpiece.

The delivery pressure inside the case is basically ambient pressure. Any excess static pressure would blow air out the exhaust. What you could be feeling is a very slight jet shooting into the mouthpiece. This could be described as a very slight stagnation (or aerodynamic) pressure. The same pressure you would feel from a blow gun.

The size of the case by itself is not a factor with venturi flow, but the geometry of the air flow is.

The small size would imply a smaller than usual diaphragm. A larger diaphragm (like the one found in a DH) does provide more mechanical advantage which normally translates into lower initial/ cracking effort.


My limited experience with Voit and Mares regulators is that they rely in a very strong venturi flow (you can see some have what they call a “vortex” tube). Their cracking effort is not as low as some others, but once flow is initiated, the required suction to maintain flow definitely goes down dramatically.

Most regulators (after 1955) have some form of venturi flow assist, but some are more dramatic than other.


I would like to add a comment about a common statement.
I always hear the term “this regulator gives you lots of air”. That is a very common statement used by many, but it is technically incorrect. All demand valves should give all the air you ask for, not any more or any less. Only the volume of air demanded should be supplied.

What the statement is referring to is how much work is required to get the air. A better description would be: “this regulator gives you lots of air with little effort” (or better yet: “this regulator gives you air with little effort”).

The effort of course is the amount of suction (vacuum) the diver has to pull to get the air.

I hope this is clear.
Luis

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Ron
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Re: Voit little gem III

Fri Apr 04, 2014 10:23 am

That is very helpful Luis, thank you.
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Re: Voit little gem III

Fri Apr 04, 2014 10:26 am

I picked one of those up off of ebay too, probably from the same seller. New hose, new diaphragm. Mine is in fantastic shape; I'm almost afraid to use it for fear of it getting dinged up. I just assumed that it was a Little Gem II, since that is what the label said and how it was advertised. I've got to go back and check out my first stage. I thought it had two LP ports. Sure is a cute little thing.

I've gone through some of the Voit catalogs, and from what I can see, they used the Little Gem III name for the first time in 1970. Looks like it was the Little Gem in 1968 (tilt valve secondary), Little Gem II in 1969 (tilt valve secondary) and Little Gem III in 1970 with a "lever action secondary." Its funny, my label is just like yours with Swimaster below the button. Prior to that, the word Swimaster was above the button with curved above it. It looks like this label change got made in the 1973 catalog, three years after they changed the name from II to III.

Edit: here's something interesting. The 1973 catalog shows the new label, but the 1974 catalog shows the old label.

Edit: My primary does have two LP ports.

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Ron
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Re: Voit little gem III

Fri Apr 04, 2014 11:49 am

Jim,

I thought mine was a II model as well, until I looked inside and saw that it was a downstream second stage and not a tilt valve. When I checked the catalogs, even the pictures of the "little gem III" say "little gem II" right on the label when you zoom in. It looks like they used the front cover off of the old tilt valve regulator, and just put the bottom box from a downstream second stage on it. It certainly is a small, cool piece of gear though. It would make a great backup regulator to throw in your dive bag, or for a deco/stage bottle.

I like this reg man. I'm going to figure out all the stuff we need to rebuild them. I know Bryan stocks it all.
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Re: Voit little gem III

Fri Apr 11, 2014 8:43 am

After finishing my rebuild on this little gem, I thought I would share what I have learned. As stated earlier, the USD first stage kit Bryan stocks in the store for the Aquarius works in its entirety on the first stage of the little gem. You can get it here:

http://www.vintagedoublehose.com/index. ... d=13974801

Provided that your second stage is a downstream, lever action second stage (the little gem III second stage, even if yours is labelled as a litle gem II) you can rebuild it using the standard second stage rebuild kit from Bryan, located here:

http://www.vintagedoublehose.com/index. ... d=12566839

If you need an exhaust valve for the second stage, which is 26mm, you can get it here as well:

http://vintagedoublehose.com/index.php? ... d=10764674

The second stage bottom box is identical to a MR-12 regulator, as is the diaphragm. The exhaust tee, mouthpiece, and second stage orifice are all interchangeable with the MR-12 as well. The top box of the regulator is unique to this style of regulator.

Pics:
20140405_231524_resized.jpg
20140405_232106_resized.jpg
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