DSV and PRAM

[INFIDELxx]

I am having my first Phoenix installed on a Royal Master. It will become my Salt water go to rig. I have decided to install a Rebreather DSV on the the loop. I have picked up a
Scott Mark 15 DSV. The diameter of the valves 1 1/8 are a little smaller than and USD valves 1 1/4 mouthpiece.

My question is how much performance will I lose by using a smaller diameter mouthpiece? Would it be very substantial? Or would the AP design in the following thread be better?

DSV for Double Hose Reg? - Rebreather World

Thanks for the help in advance.

 

[Luis H]

IMHO the existing one inch hose and the 1 1/2” valves are about the lowest size that can be used with a DH without adding too much flow resistance. Smaller has been used successfully, but it adds resistance. It is probably OK during light breathing, but I personally would not like any more resistance. Heck I re-designed the 1 1/2” valves cages to reduce the resistance when they are wet and I have measured the difference.

As far as I know, all modern re-breathers have actually gone to larger hoses and non-return valves, but they have a totally passive breathing loop with the counter lung (the divers does 100% of the work in moving the gas around the breathing loop). The open circuit demand regulator has a slight pneumatic advantage (over a re-breather) if it has a good venturi assistance during the inhale cycle. Therefore, it can get away with the traditional US Divers 1 inch hoses and 1 1/2” valve mouthpiece.


I have designed and built a couple of types of DSV that may be for sell for a very reasonable price at VDH in the near future. It is mostly up to Bryan if he thinks if there is a market for them (I have no time to build parts... I barely just have time to design them).

Actually one of the DSV is just a mouthpiece plug that fits the curve mouthpiece and the Voit mouthpiece. This is a very simple solution and it is actually my favorite style DSV for a DH. I may have some molded very soon.

The other DSV converts a reproduction straight mouthpiece into a very simple DSV. You can ask Nemrod or Robohips (at VDH) what they think about my prototype DSV.


That is an interesting thread at Rebreather World. Thanks for the link.

 

[INFIDELxx]

Luis
I would be very interested in the Straight mouthpiece conversion. I hope Bryan goes for it.
In the mean time I am going to try what was suggested the the rebreather world thread about putting bigger valves in.

That AP DSV on the Mistral 2 looks pretty good also. Check out this fine tuning blog.

http://www.therebreathersite.nl/13_Inspiration/inspiration_mouthpiece.htm

 

[Nemrod]

I have one of the Luis DSV valves and it does indeed work.

1.

2.

3.

The above pictures are taken by me of Luis demonstrating his DSV.

With a double hose you do not need to close off the airflow to the exhaust duckbill, only to close the outlet to the mouthpiece to prevent the free flow.

N

 

[INFIDELxx]

Nemrod,

Can it be operated with one hand while in the mouth? Can you tell me more about the operation. That look really good!

 

[Luis H]

Thanks Nemrod

The bubbles in picture 2 are a bit misleading. When the mouthpiece is closed there are no air bubbles leaking. I am not sure where does bubbles are from.

At Portage Quarry Roger tested another prototype and it seals great when it is closed.


This actually could be a very reasonable DSV to manufacture.


I still prefer the plug, just because the curve mouthpiece is my favorite.



I will try to post some pictures later.

 

[INFIDELxx]

Thanks alot for the information. I prefer the Voit hour glass and USN mouthpieces so maybe a plug would be my best choice. I really hope things work out with VDH.

 

[Luis H]

Nemrod,

Can it be operated with one hand while in the mouth? Can you tell me more about the operation. That look really good!

Yes, some can be operated with one hand while is in your mouth. I have made some that have a bit more friction even after I lubricate them well. In which case it helps to use both hands. I don't see that as a problem do.

 

[Nemrod]

Nemrod,

Can it be operated with one hand while in the mouth? Can you tell me more about the operation. That look really good!

Well, yes it can be operated with one hand, just a simple twist. There is no detent however so you need to use a little bit of your eyes. However it is stiff enough that it does not turn on it's own. For more details ask Luis.

The PMDSV also is still my favorite, a simple plug because I also much prefer the curved mouthpiece.

I have made a number of dives with it, one in cold water and low viz, worked like a charm but I was careful to keep track of what I was doing. The "keeper" bands act as an alignment witness.

N

 

[Luis H]

Thanks alot for the information. I prefer the Voit hour glass and USN mouthpieces so maybe a pug would be my best choice. I really hope things work out with VDH.

The plugs I made also work well with the Voit mouthpiece.

Another advantage of the plug is that I use a short lanyard to my right shoulder strap. By doing this it parks the mouthpiece always on the same spot. I just have to pull the mouthpiece and out it in my mouth.