DX Overpressure Regulator

[SeaRat]

I checked with Mossback, and he wanted information about US Diver's DX Overpressure Breathing regulator. I asked if my answer could be posted here, and he said that it could, so here it is:

Mossback,

I've been pretty busy, and so haven't checked in a while. Thanks for the message on the board. I'll answer your questions below:

John,

I was wondering if you would take a few minutes and answer the below questions regarding the DoubleHose you have that has the inner intake hose that runs from the unit to the mouthpiece.

How is the hose connected to the 2nd stage venturi?

This is a single stage design by USD, which looks exactly like a Mistral regulator, except for the inner hose design. Instead of a venturi nozzle, they used a hose clamp screwed into the same hole in the HP block. [

What is the diameter of the inner hose, ID and OD?

I don't know--I'm at work right now, and will have to get home. I think it uses about a 1/8 inch interior diameter hose (I replaced the original with a vinyl hose).

What material is the inner hose made of?

see above

How is the inner hose connected to the mouthpiece?

This is better shown than explained, but I'll try. The hose fits onto a metal tube with a hose fitting (USD used a small tinnermann-style clamp--I use plastic electrical clamps.

Does this arrangement argument some of the restriction to breathing in a heads down position?

No, but the use of a double-hose regulator does to some extent. With the single hose regulator, you are used to a positive-pressure from the regulator on inhalation. With a double hose reg, it will be negative pressure, but positional. If you are horizontal, and put your head down, the breathing effort increases as you distance your lungs from the regulator (body is in a "C" position, while the tank system is straight, increasing the negative pressure. However, if you go vertical, you place the regulator at about the same level as the lungs, and minimize this problem. But using an inner hose has nothing to do with the regulator placement, and cannot affect this change in breathing effort.

Does the mouthpiece have a smaller imushroom intake valve than the exhaust?

The USD metal mouthpiece was pretty unique. It has a restrictor plate on the intake side, with two angled slits on either side to allow air through. Over this, they placed a unique mushroom valve with a hole in the center of it. But it rotted years ago, and I never did replace it.

On the exhaust side, the only valve is the duckbill in the regulator box. There is no exhaust valve in the mouthpiece, and never was.

Is the mouthpiece smaller than the std. USD mouthpiece? It's metal isn't it?

Yes, it is smaller. You can see it on my photo in my avatar.

I presume since the reg. you have is so old in manufacture it is a 1st stage unbalanced one?

Yes, this was actually the first regulator produced by USD as a single stage unit. USD designated it the DX Overpressure Breathing regulator, and it preceeded the DY Stream-Air and DW Mistral regulators, which retained all the same parts except the mouthpiece/hose system, and the orifices.

Any other info you have would be greatly appreciated.

regards

Michael

Michael, that's pretty much the description. Fred Roberts went into this regulator pretty thoroughly in his book, Basic Scuba.

Can I post this on the thread you established to get my attention?
\
Here is an awful self-portrait of me using this regulator with it's metal mouthpiece:

And here is a bit better view of me using the regulator, two summers ago:

Note the longer hoses I put on it are from an SCBA supplier for firefighting breathing apparatus.

John

[SeaRat]

Mossback had one more question that he agreed can also be posted:

Last question......why do you like this unit so much? If there is no advantage to the inner hose delivering air direct.......

I can understand why USD stepped away from this design.

Actually, there is an advantage to this method of delivery of the air to the mouthpiece:

--There is a huge amount of air coming in, and it can catch the diver a bit unaware (especially in the 1950s, when the other regulator that USD made was the DA Aqualung. USD got complaints that the regulator breathed too easily.

--It is a quiet delivery system. The Mistral is noisy, whereas this is pretty quiet as the air is in the interior hose.

--It can use longer hoses without loosing the venturi effect. All the other regulators see an increase in breathing resistance with increasing hose length. Here, while it occurs, because of the small diameter of the hose size, and its smooth interior, length is not as much a factor.

--The longer hoses allow me to position the regulator further down on my back, decreasing the vertical distance between the regulator and the center of my lungs. This acts to minimize the breathing resistance due to regulator positioning.

The DX Overpressure Breathing regulator was unsuccessful for several reasons:

1. It had very short, stiff hoses, which tasted bad.
2. Divers were not used to an easy breathing regulator, and complained about it.
3. With the inner hoses, it is more complex than the DY Stream Air and DW Mistral regulators. Dive shops probably did not enjoy the extra maintenance.
4. With the advent of the "Kleer-E-Z" hose/mouthpiece system, the DX without non-returns would be unpopular.

John

[Broxton Coalition]

hello searat, i have been reading your post about the overpressure regulator. i bought one off ebay but it was missing the original 1" diameter hoses, the little green inner hose and the metal mouthpiece assembly. it had the kleer-ez mouthpiece setup on it.
i would like to restore this regulator to original and i am wondering if you know of any spare metal mouthpieces around and what did you use for the little green hose replacement. thanks,
mike

[SeaRat]

Vintagemike63,

I used a vinyl hose instead of the green one for the inner hose. You can get them at aquarium shops.

Restoring to the original means getting the metal mouthpiece. Check on e-bay for scuba items. I have seen one or two going in some of those sales that people have of miscellanious parts. Someone on this board may also have one. I would not go with the original hoses, as like I said they are too short, taste bad, and stiff, and most divers replaced them anyway. Dan has some very nice 1" hose with 1" ends.

If you cannot find a metal mouthpiece, we can discuss it, as the regulator could be used with a Kleer-E-Z mouthpiece system with a bit of modifications for the inner hose. I've been thinking about doing that sometime anyway.

Also, you need to check to see whether the original hose connection has been replaced by a Mistral orifice. Some were modified in this manner, and if so, you'll need to get the other fitting too.

John

[Broxton Coalition]

hello searat, the overpressure i have was indeed updated with the mistral orfice and had the kleer-ez hose/mouthpiece setup. i would like to set this regulator up as close to the original configuration as possible using newer hose/mouthpiece parts.
i had a thought that an early french mistral that had the metal mouthpiece tee might work.
looking at the internals of this regulator it looks pretty much the same as the mistral.
i was watching an overpressure on ebay a few weeks ago but it sold for $400 and that was to much to pay for the parts i needed. i thank for your input.
mike

[SeaRat]

Mike,

Here's what I thought I could do to get the "hose-within-a-hose" concept with mostly what you have. I would go to a hardware store and get either a brass or a stainless steel (preferable) hose connector with a screw-in that matches the Mistral orifice. Then run the small hose down the Kleer-E-Z hose to the Kleer-E-Z mouthpiece, with about six inches to spare. Take a spare mushroom valve cage, and drill out the center to the diameter of the inner hose, and run it through this cage. It needs to go to the opposite cage, where I would split it so that it comes to rest inside the opposite cage. I would then have to split the small hose to get it inside the cage arms, and pay attention to the length, which must be exactly correct. I would not cement it yet, as I will need to take it out, and make a one-inch lengthwise cut about 1/3 into the hose, which will become the venturi port. I would then cement the far side of that port and put it into the opposite cage, with enough cement to completely fill the hose to the venturi port (so no water can be left sitting in it). I would orient the venturi slot in the hose toward the mouthpiece, and maybe play around with it to see if it should go directly into the mouth, or somewhat off to the top if it is too great.

The original DX Overpressure has four holes in a metal tube, and the tube can collect water. If there is water in the tube, it comes out of these holes as a mist, and can be quite surprising as this mist goes down your throat (another reason this regulator fell from popularity).

While I have not actually tried this combination, I have thought it through as what I may do with my Mistral. I do not suggest that anyone else try it, unless you want to take your life in your hands with a brand new concept in diving scuba. But to me, this would combine the best of the DX Overpressure Breathing with the best of the original Mistral.

John

[SeaRat]

In addition to the above, Mossback had some other questions:

John

What is the LP pressure into the small hose, 115 psi?

There is no LP pressure on the DX Overpressure Breathing regulator. It is a single stage regulator, and so the air comes out into the nozzle at ambient pressure, but with a large velosity. If you get into the technical details, there is a pressure, but nothing like the intermediate pressure of the two stage regulator. This would be measured in inches of water pressure, according to the formula:

Total Pressure = Velocity Pressure + Static Pressure

It is used in duct systems, and I don't think it has ever been measured. The static pressure is the pressure of the air against the walls of the inner hose. The velocity pressure would be the pressure of the moving air down the tube. Add those together, and you get the total pressure. If I were guessing, I would peg it at something like 2-4 inches of water for the Total Pressure. At 0.434 psi per inch of fresh water (a calculation--I'm not real sure of right now), a 4 inch water pressure would be 4 inches of water pressure x 0.434 psi per inch of water pressure = ~2 psi. So, you see, there is no great amount of pressure against this tube, and therefore it doesn't have to hold much pressure. The vinyl hose works just fine.

John

[Broxton Carol]

there is, or was an overpressure on ebay in the last 2 days. It might still be there, I wasent following it. Check out the VOIT single stage job on there . Thats an early very rare one.