How do you setup your primary and secondary regulators/hoses for recreational?

[tbone1004]

on the simple unbalanced second stages, all of the Poseidon regs are unbalanced, and much more simple than the Scubapro style second stage. They are picky about IP, but because of their design, they do exceedingly well at depth

@halocline you and the LDS are both somewhat right in this. The IP volume in the long hose is certainly bigger so the IP drop due to demand may not be as significant as it is with a short hose, but the LDS also has a point that they probably aren't aware of and are misrepresenting. The long hose will have a larger pressure drop from source to demand when under load because of various fluid dynamic laws. This pressure drop is negligible, but it is real. Thankfully we don't treat regulators like an air gun...

 

[Storker]

The long hose actually improves regulator performance, because the air in it is pressurized. It's basically a higher volume IP reservoir. So IP drop under an equivalent demand (a breath) is less than with a short hose, because you are taking the same volume of air from a larger supply of IP.

In theory, perhaps. But is it significant? What's the ID of an LP hose?

 

[halocline]

@halocline you and the LDS are both somewhat right in this. The IP volume in the long hose is certainly bigger so the IP drop due to demand may not be as significant as it is with a short hose, but the LDS also has a point that they probably aren't aware of and are misrepresenting. The long hose will have a larger pressure drop from source to demand when under load because of various fluid dynamic laws. This pressure drop is negligible, but it is real. Thankfully we don't treat regulators like an air gun...

I don't think so. But feel free to explain these 'various fluid dynamic laws' if you'd like.

 

[halocline]

In theory, perhaps. But is it significant? What's the ID of an LP hose?

In actual diving I can't say I notice any difference. I guess you'd have to take identical 2nd stages, best would be unbalanced, on different length hoses to some depth and compare them, which I've never done. But the IP volume difference is really significant. The IP chamber in first stages is very small, and ID on LP hoses is probably around 5mm. So the difference in volume between a 30" and 84" hose is quite a lot, and both are quite bit more than the small area in the 1st stage. I would guess that replacing a 30" hose with a 7ft probably more than doubles the overall volume of IP air in the regulator. This should result in half the pressure drop for the same demand.

 

[RainPilot]

The discussion in another thread about this (way too lazy to search) came down to an LDS telling someone that the friction of the hose wall would dangerously reduce flow in a long hose. There was also a FB thing about it a month or two ago with someone spouting the same.

Yes, there will be more friction. No, it won't make any difference in any measurable way in our usage. The IP volume increase would probably more than compensate for it even if it was a thing.

Whenever someone tries to steer you away from something, toward something they sell, take with a grain of salt. There are many examples of LDS nonsense-spouting (intentional or ill-informed).

 

[DiverDownD3]

I don't think so. But feel free to explain these 'various fluid dynamic laws' if you'd like.

It's been 11 years since I took fluid dynamics and I don't really use those equations in my daily job, but in fluid dynamics there are various ways you can experience pressure loss and the length of the hose/pipe you are pumping it through is one of those ways. Like tbone said this pressure loss will be negligible, especially if we are talking about a difference of 3'.

Simple fact is anyone telling you the long hose is going to cause a noticeable pressure difference, they are full of s**t.

 

[Colliam7]

The discussion in another thread about this (way too lazy to search) came down to an LDS telling someone that the friction of the hose wall would dangerously reduce flow in a long hose.

I remember the thread, and post, but probably couldn't find it again. I remember thinking at the time that it was an unsubstantiated assertion, or at least the effect would not be measurable.

 

[tbone1004]

I don't think so. But feel free to explain these 'various fluid dynamic laws' if you'd like.

the formula is r=d*w/v where R is the reynolds number, d is diameter, w is average speed, and v is viscosity. You then have to add up a pressure drop caused by friction turbulence and things like hose fittings, elbows/swivels, etc all get added into that.

For what we do? It's not worth talking about because the drop is not going to be something anyone's IP gauge could even think about being accurate enough to measure. Maybe a fraction of a psi. Maybe one of the big ass dials that are used in hyperbaric chambers? but not likely.

Now, just because it is there, anyone who says that it is relevant, is spewing nonsense, especially if you have a well balanced second stage where an IP swing of even 5psi isn't really going to make a meaningful difference.

 

[Dish]

In actual diving I can't say I notice any difference. I guess you'd have to take identical 2nd stages, best would be unbalanced, on different length hoses to some depth and compare them, which I've never done. But the IP volume difference is really significant. The IP chamber in first stages is very small, and ID on LP hoses is probably around 5mm. So the difference in volume between a 30" and 84" hose is quite a lot, and both are quite bit more than the small area in the 1st stage. I would guess that replacing a 30" hose with a 7ft probably more than doubles the overall volume of IP air in the regulator. This should result in half the pressure drop for the same demand.

So I have identical 2nd stages... one on a long hose and one on a necklace. I will periodically clip off my primary and "exercise" my secondary (the reason for doing this could be an entirely different thread). I do not notice any difference between the two, but that is a purely subjective. I suppose if you flow-tested them on an instrumented test bench, there might be a detectable difference. As an engineer, this makes sense, but as a diver, I can't tell the difference.

BTW, my LDS meant well, but sometimes folks get mired in the dogma. I get it and I didn't bother trying to change their minds. I just dive with a long hose.

 

[tbone1004]

So I have identical 2nd stages... one on a long hose and one on a necklace. I will periodically clip off my primary and "exercise" my secondary (the reason for doing this could be an entirely different thread). I do not notice any difference between the two, but that is a purely subjective. I suppose if you flow-tested them on an instrumented test bench, there might be a detectable difference. As an engineer, this makes sense, but as a diver, I can't tell the difference.

BTW, my LDS meant well, but sometimes folks get mired in the dogma. I get it and I didn't bother trying to change their minds. I just dive with a long hose.

if you claimed you could tell a difference, you are either lying, or the regs are tuned differently.

FWIW all of the technical divers I know will take sanity breaths on their secondary at a couple points during the dive. I will usually do it at the end of my descent, about 5 mins before ascent, and then again at the start of ascent as these tend to be the times where something is more likely to go sideways where I would need to actually use it. I'm on sidemount most of the time so I use mine equally in that sense :-D