Hookah ,diy

[newhaul]

Seems to my untrained eye/ears that someone is trying for a darwin award.

[Zai]

The math is correct but not complete, because you also need to factor in volume and the rate at which you need the volume.

[Laughing Buddha]

Originally Posted by Zai

The math is correct but not complete, because you also need to factor in volume and the rate at which you need the volume.

Just to clarify please - Is this with regards to Post #124, or the more recent ones?

As a refresher; Cubic Feet Per minute is a Volume/Rate measure. Demand is based on the work effort described in RMV and adjusted for atmospheric pressure (at depth).

As a point of fact, Gold dredge Divers do use Low Pressure/Low CFM pumps. The Thomas T80 produces on the order of 35-40 psi (sold by Keene engineering) and 1.8 CFM @ 45 PSI. Again they are usually at a "snorkeler's depth."


Personally, I'm looking for 2.0 CFM @ 90 PSI, 12v, 100% Duty Cycle, of reasonable quality/price, and I can fit in my luggage.


Cheers - Jim

[transmitterdan]

Originally Posted by denverd0n

Make sense?

Not really. The pressure required is a lot more than atmospheric. The demand regulator needs about 100psi to function as an effective underwater breathing device. The demand regulator needs high volume flow during air intake with periods of no flow. So some reservoir is needed. It's quite a bit more complex than delivering a constant air flow at 1 or 2 atmospheres of pressure.

[a64pilot]

When you get to Tri-mix and other forms of technical diving, you calculate your SAC rate, or surface air consumption. Mine is .67 cu ft per min swimming which is I think about average for your average older out of shape fat guy. Young studs and our fairer sex will use much less. My cave diving instructor honest to a god his SAC rate was like .25 or something crazy.
Just don't start skip breathing trying to conserve air.
I cu ft per min at 90 PSI is fine for me at 6', two is a comfortable cushion, but it would only take me to about 40' or there about.

You can get low PSI regulators, I bought a Hooka max or something that was supposedly set for 80 PSI. Absolute piece of junk, I threw it in the trash and adjusted one of my Dive rite regs IP. It works great.
However you do not need an expensive balanced reg for a Hooka, an unbalanced one is fine as your not breathing at any real depth

[Zai]

Originally Posted by Laughing Buddha

Just to clarify please - Is this with regards to Post #124, or the more recent ones?

As a refresher; Cubic Feet Per minute is a Volume/Rate measure. Demand is based on the work effort described in RMV and adjusted for atmospheric pressure (at depth).

As a point of fact, Gold dredge Divers do use Low Pressure/Low CFM pumps. The Thomas T80 produces on the order of 35-40 psi (sold by Keene engineering) and 1.8 CFM @ 45 PSI. Again they are usually at a "snorkeler's depth."


Personally, I'm looking for 2.0 CFM @ 90 PSI, 12v, 100% Duty Cycle, of reasonable quality/price, and I can fit in my luggage.


Cheers - Jim

It was in response to post 135, I guess I should have quoted it.

[hellosailor]

I don't think the OP will find any compressor "manufacturer certified" for Grade E quality air. The quality of the air coming out of any compressor depends on not just the compressor, but on the quality of the air going into it, and the maintenance and sometimes filters that the USER must inspect and control.

If the compressor is guaranteed to be "clean" and non-contaminating from the factory, that's about all the manufacturer can guarantee. The operator has to deal with the rest, and that includes having the rig TESTED for air quality on a regular basis.

[denverd0n]

Originally Posted by Zai

The math is correct but not complete, because you also need to factor in volume and the rate at which you need the volume.

Which, of course, would be why I specifically mentioned volume as an issue. But the volume required is largely independent of the pressure at which it must be delivered. I was looking at the pressure side of the equation. I think Laughing Buddha did an excellent job of addressing the volume side.

Originally Posted by transmitterdan

Not really. The pressure required is a lot more than atmospheric. The demand regulator needs...

Which, of course, would be why I specifically mentioned the regulator as an issue. Regulators are already made for hookah systems that do not require as much air pressure as normal SCUBA regulators. How low can they go, and still function? I don't know. Which is why I didn't try to answer that question. I am, however, absolutely certain that it is much less than 100 psi. I have seen regulators for sale -- intended for hookah, and other types of low-pressure systems -- that will function down to around 40 psi.

Oh, and as for the comment about the Darwin award... The operative word in that sentence is "untrained." Every thread about DIY hookah systems has to have its obilgatory post about how we are all going to die if we don't buy expensive, commercially-made systems. Great. Thanks. Now can we get back to the discussion at hand?

[wedivebc]

Originally Posted by denverd0n

I need to do more research into this, but...

If you apply 14.7 psi of pressure to air in a tube that runs from the surface down into the water, you will push the air down approximately 33 feet. Double the pressure, double the distance down that you push the air column. So, just getting the air down to that depth does not take a lot of pressure.

The question then becomes, how much additional pressure is required -- beyond what gets the air down to that depth -- in order for a human to breathe the air through a regulator of some sort? I cannot imagine that the required delta is all that much.

Hence -- again, with minimal actual research, but just reasoning this through -- I do not see where 90 psi at the surface would be required for relatively shallow diving. It seems logical to me that 45-50 psi would be more than enough for dives less than 30 feet. In fact, it may well be that 50 psi is completely adequate for dives down to 50 feet.

As mentioned, I do intend to look into this more.

Of course, as fstbttms said, we may be WAAAAAY over-thinking this. :-)

A scuba regulator typically operates on an intermediate pressure of ~140psi which is usually depth compensated by the 1st stage regulator to remain 140psi over ambient pressure. I doubt a regulator being fed 90psi from the surface would perform very well at 33ft.

[accomplice]

Originally Posted by wedivebc

A scuba regulator typically operates on an intermediate pressure of ~140psi which is usually depth compensated by the 1st stage regulator to remain 140psi over ambient pressure. I doubt a regulator being fed 90psi from the surface would perform very well at 33ft.

Hookah regulators are slightly different from SCUBA regulators in that they regularly operate at 90psi. I have this one XS Scuba Hookah Second Stage Regulator which is spec'ed for 80-110psi.

I do not know if it would work well below 80psi. Getting air down to depth is only one part of it -- giving the diver sufficient quantity and pressure of air may be another. The regulators are tuned such that with slight negative pressure (inhale) they allow the compressed air to pass.

[denverd0n]

As already posted, I have seen regulators sold specifically for hookah use that will work down as low as 40 psi. I don't know if it is possible to make a functioning second-stage that would work with even lower hose pressures, but it wouldn't surprise me. Second-stage regulators, after all, are pretty simple devices that work on spring pressure. Adjust the pressure of the spring correctly and I see no reason why one could not be made to work with hose pressures that are just barely above the ambient pressure.

[newhaul]

The problem I see imho is that it takes pressure to force volume thru a set size hose to the regulator when drawing a breath .

[a64pilot]

Originally Posted by accomplice

Hookah regulators are slightly different from SCUBA regulators in that they regularly operate at 90psi. I have this one XS Scuba Hookah Second Stage Regulator which is spec'ed for 80-110psi.

I do not know if it would work well below 80psi. Getting air down to depth is only one part of it -- giving the diver sufficient quantity and pressure of air may be another. The regulators are tuned such that with slight negative pressure (inhale) they allow the compressed air to pass.

That is exactly the one I apparently purchased on January 22 and threw in the trash soon after. Even if it breathed worth a hoot the way it's built it is very uncomfortable. It hit your nose or chin or something, I don't remember but it's not worth having, money wasted.

It's dead easy to adjust a regular reg's cracking pressure, I adjust mine so when the knob is full out they free flow just a little, turn the knob in some and they stop.

[denverd0n]

Originally Posted by newhaul

The problem I see imho is that it takes pressure to force volume thru a set size hose to the regulator when drawing a breath.

Good point. Does anyone know how to calculate the additional pressure required to overcome hose restrictions? I don't.

On the other hand, it takes less than 5 psi to push air down 10 ft, assuming no hose restrictions. I am simply not going to believe that you REQUIRE an additional 80 psi to overcome the hose restrictions.

My guess would be that the hose restrictions, even with a 50' hose, add only a couple of psi at most.

And, yes, again, I realize that I am grossly over-thinking this. I am just curious what the real minimum requirements are, versus "stuff with these specifications are readily available, so why not just use them?".

ADDITIONAL:

Okay, so I went and did some looking. 50' of 1/4" ID hose will introduce a pressure drop of 1.6 psi. So, pretty insignificant.

Which means, if you want to go down 30', and have the air presented to your lungs at a "sea level," 14.7 psi, you need less than 30 psi at the surface pushing the air down.

On top of that, you probably need a couple more psi to overcome resistance in fittings and so forth, and then whatever your regulator requires as a minimum pressure.

[transmitterdan]

At what air flow delivery rate did you calculate 1.6psi drop for 50' of 0.25" hose? I think your calculations need a bit more work.

Breathing is not a constant air flow application. There will be high flow followed by periods of no flow. The industry uses the pressures they do because it works. Regulator design pressures were not generated by a random number machine. They are based on calculations and literally decades of testing.