Double hoses and trimix?

[John C. Ratliff]

Duckbill, thanks--it was late--edits made.

John

 

[John C. Ratliff]

Nope, trick question. At a around 6000 ft the ambient pressure would equal that of a full (3000psi tank). That depth, the internal pressure and extrenal pressure of the tank are the same so no gas would flow into the reg and the hoses would start to collapse. If however, the reg was being supplied from a pressure source that was capable of keeping at least a few psi over ambient going into the reg then you are correct, the hoses would never collapse...

Use a 4500 psi tank and you can send it, unmanned, to 10,000 feet without experiencing a hose collapse. But I don't think it likely that any diver will experience this...hopefully.

By the way, both Cousteau and Fred Roberts recognized the value of doing this, and pressurized their camera systems. Cousteau did it by attaching a small cylinder and regulator to his motion picture cameras so that they always were at ambient pressure. Fred Roberts drilled his double hose can, put a hose adapter on it for a very small hose, which he ran to his underwater camera. These measures meant that these camera cases were never subjected to high pressures as they descended. Both had less worries of flooding their expensive cameras because of this.

SeaRat

 

[duckbill]

So tell them, those that are theorising and not me.?

I'm sorry. I thought you were attempting to determine how much external pressure the hoses could take with your brick experiment.

So if you could put John C's formulae away and use your practical brain,
I'm still wondering of what these hoses will have in them that is 135psi,
when it takes a puff of breath at any depth to open the non return valves
despite the fact that even if sealed these hoses cannot handle that pressure?

I'm having a bit of trouble following your question.
If the pressure outside the hoses is 14.7psig at 33fsw, then the pressure inside the hoses will also be about 14.7psig.
If the pressure outside the hoses is 100psi, then the pressure inside the hoses will also be about 100psi.
If the pressure outside the hoses is 135psi, then the pressure inside the hoses will also be about 135psi.
There will never be 135psi difference in pressure, if that's what you mean.
I hope this helps.

 

[oldmossback]

What Captain described in Post #15 is the basis of the Cousteau-Gagnan patent for the Aqualung. But concerning the pressure in the hoses, what Duckbill is describing is that the ambient pressure at 270 feet of sea water is at least 135 psi. 270 feet divided by 33 feet per atmosphere is 8.18 atmospheres (gauge; it is actually 9.18 atmospheres absolute--with the atmosphere itself counted). If you then multiply that 9.18 atmospheres absolute by 14.7 psi per atmosphere, you get 134.946 psi absolute, or 135 psi absolute.

But, and this is significant, there is not 135 psi difference between the inside hose pressure and the outside ambient water pressure, as both sides of the hose experience approximately the same pressure. There is at most about 12 inches of water pressure difference due to positional differences between the mouthpiece and the LP diaphragm of the regulator. I was taught that there is a difference in water pressure for salt water (it's slightly less for fresh water) of 0.445 psig per vertical foot. So the difference between the ambient water pressure and the mouthpiece is probably at most 0.445 psig. Therefore, the greatest pressure which would be on a double hose regulator would most likely be about half a psi (0.5 psig). By the way, there is a slight difference between the exhaust mushroom of most single hose regulators and the center of the diaphragm, which in some positions can cause a single hose regulator to leak air if it is extremely well tuned--has less than about 3/4 inch breaking pressure.

The diagram in Let's Go Diving by Bill Barada is a little different, in that it shows the difference between the demand second stage diaphragm and the center of the lungs. This is how we as divers sense ease of breathing--the difference between the lung pressure and the regulator's LP diaphragm placement in the water column. This diagram is meant to show the difference between the single hose and the double hose for different positions. In a "normal" swimming position, the double hose regulator has "negative pressure, two hose--equals hard inhalation, easy exhalation." For a single hose regulator, "positive single-hose equals easy inhalation, hard exhalation." It was the hard exhalation which kept the single hose regulator from being accepted by the U.S. Navy for many years--not until the AMF Voit MR-12 came along did the U.S. Navy accept a single hose regulator; it had a larger exhaust than its competitors, and forced U.S. Divers to come up with a modified Conshelf and the third generation of the Calypso.

SeaRat

John

That's close to what I was figureing......my calulations were .46 at 8 inches deeper than the reg......using a 6 foot tall man's chest thickness........in a head down position.

With my experiments, there is no noticeable difference with a hose in hose set up until one is in a head down position.......senses make you feel like your breathing a hybrid single/double hose, at least to me...........but head down, the breathing effort is the same as head up........so there is some value however, I'm not sure the expense and effort is warranted............it's easier to teach someone to just roll to their side for extra air head down...........

 

[JS1scuba]

I have run mix a few times, mostly 21/30 or 21/35. The major problem is lack of back gas tank size as all of my large tanks have DIN tank mounted valves, which pulls the cans to one side so you need a hose set with two lengths, so I have to run my 72's which is not enough for me past 140 or so. The other problem is parking the mouth piece out of the way for using any deco gasses in such a way as not to get freeflows.

Louis has a mouth piece design that should work to close off the mouth piece for deco parking but I haven't seen Bryan bring it out yet.

Pete, you can do it fairly easily with an older USD center manifold put on 3/4 thread steel 120s (7.25" diameter) and then for gas switch change the mouthpiece DSV to a draeger from a dolphin that you can close off and then go to off-board bottles with single hose regs for deco.

your new triple 72s will work fine as well.



cheers
jds

 

[Luis H]

I have run mix a few times, mostly 21/30 or 21/35. The major problem is lack of back gas tank size as all of my large tanks have DIN tank mounted valves, which pulls the cans to one side so you need a hose set with two lengths, so I have to run my 72's which is not enough for me past 140 or so. The other problem is parking the mouth piece out of the way for using any deco gasses in such a way as not to get freeflows.

Louis has a mouth piece design that should work to close off the mouth piece for deco parking but I haven't seen Bryan bring it out yet.

Pete

In addition to the vintage style DSV that I designed and built, I also have been using a mouthpiece plug. I actually prefer the mouthpiece plug because it works great with the curve vintage style mouthpieces (which is my favorite).

I actually don’t like the mouthpiece bite on the straight vintage mouthpiece. Therefore I don’t really like to use my vintage style DSV.

I attach the mouthpiece plug to my right shoulder strap D ring. This parks the mouthpiece in a convenient place when I switch to deco/ stage bottles. I actually sometimes don’t even bother with the plug and just put the DH mouthpiece under my chin. I then route the single hose from my stage regulator over my double hose and that holds the hoses down.

On post number 19 of this thread you can see the mouthpiece plug on my right shoulder.
http://www.scubaboard.com/forums/vi...atest-technical-diving-regulator-phoenix.html


I will be glad to send you one of the mouthpiece plugs prototypes if you want to try it.
Send me an email with your address.

We can also work out something if you are interested on trying the vintage style DSV.

 

[John C. Ratliff]

John

That's close to what I was figureing......my calulations were .46 at 8 inches deeper than the reg......using a 6 foot tall man's chest thickness........in a head down position.

With my experiments, there is no noticeable difference with a hose in hose set up until one is in a head down position.......senses make you feel like your breathing a hybrid single/double hose, at least to me...........but head down, the breathing effort is the same as head up........so there is some value however, I'm not sure the expense and effort is warranted............it's easier to teach someone to just roll to their side for extra air head down...........

We a lot of times don't realize that even a small change in the pressure from the water column has some effect on us. Years ago, I had a USD full face mask set up with the double hose regulator (DA Aquamaster, I believe). Anyway, I could tell the difference because when I leaned over to observe and photograph some amphipods on an anemone, I could feel the pressure difference and it bowed in my cheeks. Without a mouthpiece in my mouth, it was easy to detect the difference in the pressure. It is a totally different feeling.

If you want to get a good idea of how much 14.7 psi is when it is applied unevenly to a surface, view this experiment. What is happening here is that the can is filled steam from the small amount of boiling water. By placing the can upside down into the water, it does two things. First it creates a barrier to air coming into the can, and second it cools the steam. The steam then condenses into water, leaving a vacuum inside the can. Air pressure then crushes the can. Here is another good demonstration of water pressure, from a diver's perspective. The interesting thing about this demonstration is that the presenter has it a bit wrong. If you convert 1 kg/cm2 into psi, it comes out to about 14.2 psi. He was at 20 meters depth, and he stated that there was 3 kg/cm2 pressure on the side of the can. Actually, the 3 kg/cm2 was the "absolute pressure," which counts the atmospheric pressure. He was at 3 atmospheres absolute, which is 2 atmospheres gauge pressure (28.4 psi using that converter, or 29.4 psi using the value of 14.7 psi/atmosphere). This is because there was already air inside the container at 1 atmosphere absolute pressure (1 kg/cm2). This also shows how much easier it is to use the Metric System to track atmospheres, as it is based upon water.

Our diving hoses do not have that kind of pressure differential. But even a little is enough to feel in breathing effort.

SeaRat

 

[Gilldiver]

Joel and Luis

As far as I am concerned, the triple 72’s are more of a “what can I do if I wanted to” than a practical solution to a diving problem. As Joel knows, if I’m going deep, I will most likely be going inside something, the triple 72’s are just too wide to penetrate with (I couldn't get them through the hatches of the U-Boat or the USS Bass), I’d much rather use one of the 3 sets of 130’s that someone left in my garage or my set of 72's/80's/100’s when doing that. Plus, the mass distribution of the triples is way wider then twins and require planning ahead and more effort to control, so getting back up onto the boat in any type of seas could be problematical.

If I want to do some deeper stuff with my double hoses, I’ll take the double 72’s and a bottom stage and a deco bottle, that should take me for most of the wrecks over here down to the Suffolk and the Bass. The manifold will be revised with shorter cross bars for triple 30’s or 40’s this winter for use on wrecks down to the U-boat. In both of these cases, the mouth piece plug should work out nicely.

 

[Gilldiver]

On one of the other boards someone suggested that I take my triple photos into B&W for a more 1960’s Skin Diver look:

Here is how USD did triples in the 1967-1969 catalog

 

[John C. Ratliff]

Pete,

I was wondering why that plug was in the cross-over manifold. Thanks,

SeaRat