More aggressive venturi action on a RAM/DAAM?

[elmer fudd]

Just wondering if anyone has tried altering a RAM or DAAM for a more aggressive venturi effect. Seems like it would be fairly easy to do and because of that, I suspect someone here has already tried it.

I was thinking along the lines of plugging or partially plugging one or more of the two second stage ports that don't face the hose.

My understanding is that if the venturi is too strong that the diaphragm will collapse upon inhaling creating a free flow, but I'm wondering if it is possible to make it significantly stronger than stock.

 

[Luis H]

Yes, you can easily get into a free flow condition.

I can tune my regulators so it is almost in a free flow condition without modifying the second stage nozzle.

When I am done diving, before I take of my tank, I often will intentionally induce a free flow on my regulator by just inhaling while taking the mouthpiece out of my mouth. The free flow with dry tank air helps dry off the hoses.

What you are suggesting to do have been tried a number of times and it can be somewhat effective if the regulator is not well tuned. If the regulator is well tuned, it can be in the borderline of uncontrollable free flow very easily.



Warning
Never inhale directly from the horn of a double hose. It can be done, but with the strong venturi you take the risk of an air embolism.
If you are going to play with enhancing the venturi, be extremely careful when testing it.
Now a day, I always use a hose with a mouthpiece and an exhaust valve when I inhale from a DH regulator.

 

[elmer fudd]

Thanks, I knew somebody must have done it.

Neither of my RAM's are at the point where I can induce a free flow just by inhaling right now, but I'm thinking that I'm going to fool around with one of them tonight after work and see if I can't get it there.

 

[captain]

Experimented with it and couldn't improve on a well tuned regulator.

 

[John C. Ratliff]

I have thought of adapting the Aquamaster second stage housing by putting screw threads into the three openings, then plugging two of them (maybe with a very small hole in them) and screwing in a Mistral nozzle looking down the hose. 'Just a thought, but appealing ever since I saw the US Navy Experimental Diving Unit graphs on both the Royal Aquamaster and the Mistral from 1958.

SeaRat

 

[DrunkenParrot]

I have thought of adapting the Aquamaster second stage housing by putting screw threads into the three openings, then plugging two of them (maybe with a very small hole in them) and screwing in a Mistral nozzle looking down the hose. 'Just a thought, but appealing ever since I saw the US Navy Experimental Diving Unit graphs on both the Royal Aquamaster and the Mistral from 1958.

SeaRat

Good info, thanks for sharing.

 

[herman]

Something else to consider, that seat holder (nozzle) is one of the unreplacable parts.... if......make that when... you mess it up. There may be a rare few around as spares but I don't recall seeing any. The wall material around the holes is fairly thin and will take a careful hand to tap and thread. If you seriously want to play with it, my suggestion would be to first reproduce the holder.......it is 5/8 inch with a 24 pitch thread....trust me, I know.

 

[captain]

I enlarged the hole pointing down the hose as much as I could and then soldered a tube on it to simulate the Mistral nozzle. It was much worse. Increasing the size of the one hole pointing down the hose may make a slight improvement but not much. Best to leave it alone.

John, There is not enough material to thread the hole and screw in a Mistral nozzle. You would have to make an entirely new seat holder to do it, that is why I soldered a tube to it.

 

[elmer fudd]

Something else to consider, that seat holder (nozzle) is one of the unreplacable parts.... if......make that when... you mess it up. There may be a rare few around as spares but I don't recall seeing any. The wall material around the holes is fairly thin and will take a careful hand to tap and thread. If you seriously want to play with it, my suggestion would be to first reproduce the holder.......it is 5/8 inch with a 24 pitch thread....trust me, I know.

I bought 3 DH regs and a Voit MR12 along with a bunch of spare parts from a dive shop manager a few months ago, so while they might be rare, I happen to be sitting on about half a dozen of them.

I wasn't thinking of threading them however. I'm thinking more along the lines of making drop in plugs that will be inserted from the inside. If I were to make them snug, so that friction would hold them in place, and then make a small head so that they wouldn't be pushed through the hole under pressure, I think that might work. It'll be a bear trying to machine something that small though.

I personally feel that a Mistral style nozzle probably isn't necessary.

 

[Luis H]

Something else to consider, that seat holder (nozzle) is one of the unreplacable parts.... if......make that when... you mess it up. There may be a rare few around as spares but I don't recall seeing any. The wall material around the holes is fairly thin and will take a careful hand to tap and thread. If you seriously want to play with it, my suggestion would be to first reproduce the holder.......it is 5/8 inch with a 24 pitch thread....trust me, I know.

I totally agree with making some reproduction seat holder/ nozzle and not modifying the original one.

The thread size I have measured for the US Divers is actually 5/8” - 28 tpi UN.
The Voit Trieste uses 5/8” – 24 tpi UNEF.

In the US Divers nozzle there are normally only two male threads so it is hard to measure. You need to double check it in the female threads of the main body.

I will triple check the thread pitch later, but this has been double checked by a couple of people.

I don’t think that US Divers ever used the 5/8”-24, but you may also have an odd unit.