Performance loss regulator with long hose setup?

[Luis H]

Well....yes and no. Volume wise, you are taking a very small volume and making it only slightly bigger. But since the volume of the intermediate air passages of the average first stage, including the second stage hose, the inflator hose and the hose for the octo are still fairly small, doubling or tripling the lenght of the primary hose still adds a significant percentage to the total volume.

The difference in volume can be roughly measured just by turing off your air and seeing how many full and partial breathes breaths you get with the short hose and then the long hose attached. It can be measured much more accurately in terms of IP drop and recovery with the needle swing on an IP gauge during and after inhalation.

The difference will be there, but the difference also will not amount to a noticeable increase in performamnce.

It is kind of interesting that I have been getting reports from many Phoenix RAM owners that their PRAM breathes better than even a well tuned comparable RAM.

I tend to think that the difference is probably more related to the fact that most PRAM are equipped with silicone diaphragms, the best mouthpiece valves available, and are highly tuned (and perhaps also some wishful thinking or optimism). But, I have always wondered how much of a difference all the extra volume from the LP hose attachments could be making on the regulator performance.

I am referring to a double hose regulator were the first stage is the same as a Conshelf and the second stage is right next to it in the same brass body, no LP hose needed.

Comparing a bare RAM (with no LP hoses attached at all) to a PRAM with an octopus, LP inflator, etc. the ratio of volume from one to the other is huge.

I have tried testing one against the other, but the moment I add an IP gauge I am affecting my measurements since I don’t have a real short LP hose. Any LP hose and even the gauge itself will affect the measurement (a classical dilemma in instrumentation design: “any time you measure something you affect the measurement, to some degree”).

The bottom line is that my observations seem to show that the IP does stay a bit more constant with multiple LP hose, but it is really hard to tell. In either case the IP variation is small enough that I would need better instrumentation (with recording capabilities) and a more controlled breathing simulator to truly be able to measure the difference (in the transient conditions of the breathing cycle). Again, I am not even able to test a truly bare RAM.

 

[Flightlead]

the hose has a pretty high Reynolds number.....

 

[BMCG]

ahh a Chemical Engineer in our midst...

 

[Flightlead]

Chemical engineering? Isn't that like cooking?

 

[BMCG]

Indeed..although always thought Plumbing was the more appropriate analogy

I'll raise you a Nusselts number

 

[Charlie99]

The difference in volume can be roughly measured just by turing off your air and seeing how many full and partial breathes breaths you get with the short hose and then the long hose attached.

[slight hijack] -- but the original question has been beat to death ---

I'm pretty sure that except perhaps with a near empty tank, that the air you can breathe after turning off the valve is mostly air that has been on the HP side, not on the IP side. The fact that the SPG moves partway to zero during each breath kind of supports this.

Your short hose/long hose test will probably result in the same number of breaths after shutting off the valve.

 

[DA Aquamaster]

[slight hijack] -- but the original question has been beat to death ---

I'm pretty sure that except perhaps with a near empty tank, that the air you can breathe after turning off the valve is mostly air that has been on the HP side, not on the IP side. The fact that the SPG moves partway to zero during each breath kind of supports this.

Your short hose/long hose test will probably result in the same number of breaths after shutting off the valve.

As long as you control for it by having the same HP side accessories attached and by ensuring the supply pressure is in the same range (+/- 100psi) for each condition it won't matter.

 

[DA Aquamaster]

the hose has a pretty high Reynolds number.....

That would open up a whole new can of worms - for example what is the flow velocity and reynolds number for air flowing through a scuba hIse? Way back when I could determine it for an airfoil section, but I never tried it with a hose.

Then again the difference over an additional 3 or 4 ft of hose is still probably very slight. Practically speaking you can pump a lot more water through a 5" fire hose than you can through two 3" fire hoses despite the greater area represented by two 3" hoses due to the fluid dynamics involved, but that argument did not transfer well to scuba applications when companies tried to go to 1/2" LP hoses from 3/8" LP hoses. with no noticeable improvement.

 

[AbyssalPlains]

I recently switched to a long hose and actually DID notice an initial cracking effort necessary to draw air from the reg that I didn't notice before. It's an Atomic that has always breathed completely effortlessly. Now, I have to draw slightly harder at the beginning of a breathing cycle before the air comes streaming in.

However, in light of everything that was said above, perhaps it's my reg that needs service. I haven't had it serviced in three years, so that might be the true origin of the issue.

 

[NAUIwowee]

I recently switched to a long hose and actually DID notice an initial cracking effort necessary to draw air from the reg that I didn't notice before. It's an Atomic that has always breathed completely effortlessly. Now, I have to draw slightly harder at the beginning of a breathing cycle before the air comes streaming in.

However, in light of everything that was said above, perhaps it's my reg that needs service. I haven't had it serviced in three years, so that might be the true origin of the issue.

Back in 2002, SP set a record by having 74 divers, breathing through 115 meters of low pressure hose, breath off one MK25 first stage. See this link: Scubapro record Based on this, I don't think a slightly longer hose would be an issue. Like you said, it may be that your reg needs service.