Why can't scuba tanks be set up like a firefighter's scba?

[DaleC]

I'm not clear on what you're saying - is it that one has to redesign the valve system to dive inverted? If so, someone should tell Akimbo.

The idea of HP tanks is interesting and I bet a lot of people would like to be able to use smaller tanks of the same volume but my limited experience has been that getting HP fills is problematic even now with 3400psi tanks. Pumping those higher psi's seems to create more wear and tear on the compressor and getting a somewhat accurate hot fill means going up into the high 3000's. I could imagine 4500 rated tanks for scuba would come with a whole bunch of increased cost to compensate compressor wear and with increased hydro/vis requirements imposed by nervous filler operators.

What would completely solve the problem would be for a certain cave diver to begin adopting the system, along with his affiliated company making the cage. Then, everybody would want one and it would become the new "right way" to dive.

Laugh if you want but you know it's true... can anyone say "infinity"

 

[beanojones]

A simpler fix in my mind to fix the head hits tank senario is higher pressures. Make tanks that are 4500psi. Smaller tank size more cubic feet of air. We switched to high pressure tanks 12 years ago. World of difference in size of the cylinders for the same amount of gas. Alot of compressors are already rated for 4500psi and any new one could be speced at 6000psi to fill cascade systems.


Disclamier: I am definatley not a scuba expert, just putting in my .02 in reference to scba

Buoyancy swings are greater with higher pressure tanks, and time between service for first stages would shorten with hight pressure tanks are the usual reasons given.

Plus aluminum tanks are cheap and easy, and the fiber wrapped tanks for higher pressure are horrible in seawater, and get damaged too easily.

 

[FFPEREZ]

I'm not clear on what you're saying - is it that one has to redesign the valve system to dive inverted? If so, someone should tell Akimbo.

I wasn't very clear. If you want a scuba set up the same way a scba is set up yes you would have to redesign the first stage. Can use current products yes but then you get into finding guards or cages to protect the first stage and valve hanging below the cylinder. In a scba the valve is down then a high pressure hose is run up to about the middle of the cylinder where the first stage is located. Essentially protecting the first stage from damage.

Buoyancy swings are greater with higher pressure tanks, and time between service for first stages would shorten with hight pressure tanks are the usual reasons given.

Plus aluminum tanks are cheap and easy, and the fiber wrapped tanks for higher pressure are horrible in seawater, and get damaged too easily.

Didnt consider the buoyancy swings, but they do make steel tanks rated for 4500psi. If regs are designed for higher pressures surely manufactures could keep the service intervials the same.

 

[Akimbo]

I just got back after a week where I used the doubles rigs again. I am still not satisfied with the hose management but it is getting closer. I will let you know if I get it all worked out (or give up and call it good enough).

… If you want a scuba set up the same way a scba is set up yes you would have to redesign the first stage….

I have not had any problem with first stages diving valve-down on these recreational rigs or on commercial bailouts. However, the hoses had to be 18-24" longer.

…Can use current products yes but then you get into finding guards or cages to protect the first stage and valve hanging below the cylinder….

The only commercially available valve-down protectors I have found are made in the UK by Custom Divers. I would have just purchased theirs except I wanted more protection. You can use a yoke with theirs, which you can’t with the ones I built.

… In a scba the valve is down then a high pressure hose is run up to about the middle of the cylinder where the first stage is located. Essentially protecting the first stage from damage….

I have never seen a rig like that. Do you have any links? All the SCBA rigs I have seen are valve-down and the first stage mounts directly to the valve. Then an LP hose runs up. My absolute favorite doubles are the AGA Divator 324s, now Interspiro



As you can see from the photo, the valve, first stage, and LP hose is fairly well protected. The name 324 comes from 300 Bar/4351 PSI, 2 bottles, 4 Liters (3.8 really). I measured the cylinders alone empty in the water at -9.9 Lbs and -16.3 Lbs full so they are really only useful in cold water where you have suit buoyancy to compensate for.

…Didnt consider the buoyancy swings, but they do make steel tanks rated for 4500psi. If regs are designed for higher pressures surely manufactures could keep the service intervals the same.

The only manufacturers I could find that rated their first stages for 300 Bar/4,351 PSI continuous-operation were Atomic, Poseidon, AGA/Interspiro, and Aqualung/Apex — excluding the unbalanced first stage Calypso. Any regulator with a DIN will take the pressure but the seat life is reduced. I have used some older Oceanic flow-through piston first stages without trouble but Oceanic recommends against it on current models.

 

[Akimbo]

Buoyancy swings are greater with higher pressure tanks, and time between service for first stages would shorten with hight pressure tanks are the usual reasons given...

How does that work? Full to empty buoyancy swings are the weight of the air (effectively volume) regardless working pressure — about 0.08 Lbs/Ft³ depending on moisture level.

Agreed on the height issue though. Unless you are really tall it would be hard to wear a Worthington HP 120 valve-down. I am 5'6" and have to shift the bottle to reach the valve on a steel 80 valve-down and have it low enough my head doesn't touch the tank boot.

 

[MRadke]

I could be wrong but I think that what FFPEREZ is referring to is the fact that the valves on fire service bottles are made with a heavy bumper that the bottle is designed to be stored on, with male threads set at a right angle to the bottle and most importantly, a REMOTE first stage. I think it could be done easily with a beefed up valve, with high pressure hose connecting a first stage mounted somewhere on the pack. On the SCBA that I started with, the first stage was mounted on the harness at the left hip.

The newer models have a high pressure line from a first stage located in the backplate directly to a mask mounted regulator. AirHawk® II Air Mask in Supplied Air Respirators | MSA US

In the picture, you can see the reg at the end of the hose on the left front of the pack. The right front has a second hose coming over the shoulder with a pressure gauge.

 

[FFPEREZ]

I could be wrong but I think that what FFPEREZ is referring to is the fact that the valves on fire service bottles are made with a heavy bumper that the bottle is designed to be stored on, with male threads set at a right angle to the bottle and most importantly, a REMOTE first stage. I think it could be done easily with a beefed up valve, with high pressure hose connecting a first stage mounted somewhere on the pack. On the SCBA that I started with, the first stage was mounted on the harness at the left hip.

Yes that is what I was referring too with the remote first stage. I started with the first stage mounted to the hip also. Have 3 surplus ones in my garage now that they have became obsolete.

The square box to the left of the cylinder with SCOTT on it is the first stage

To the OP depending on how close you want a SCUBA setup like a SCBA, manufactures aren't making components the same. It has been proven in this thread you can mount a SCUBA tank valve down, but it has been shown somethings have to be changed to make it work.

Back on the high pressure bottles. Sorry I meant in the SCBA world most tanks are 4500psi and steel tanks can still be found. Everything in the fire service has changed from 2216psi to 4500psi. Some speculation has been that there might be another pressure increase to 6000psi. When the change started it was many years before all the compressors and storage systems caught up, now 6000psi models are integrated into most all departments. This change was brought on by the obvious benefits of more cubic feet of air, in a smaller LIGHTER(important in the fire service) cylinder.

I have a feeling if the demand in the SCUBA market for high pressure fills was great enough most shops and dive ops would be starting to phase in HIGH pressure systems when upgrading their current compressors and storage banks. This will take time to be done (years). With the ever so common AL80 the demand for high pressure systems isn't has high to dictate a rapid change to a higher pressure.

Akimbo I really like your setup:cool3:

 

[Akimbo]

I could be wrong but I think that what FFPEREZ is referring to is the fact that the valves on fire service bottles are made with a heavy bumper that the bottle is designed to be stored on, with male threads set at a right angle to the bottle and most importantly, a REMOTE first stage. I think it could be done easily with a beefed up valve, with high pressure hose connecting a first stage mounted somewhere on the pack. On the SCBA that I started with, the first stage was mounted on the harness at the left hip.

I can't tell from that photo but it seems very odd that they would run HP through a high-flow hose instead of mounting the first stage directly to the valve. Are you sure the cylinder connection at the valve doesn't drop to an intermediate pressure (500-1000 PSI???) before entering another pressure reducing regulator, and finally the demand regulator mounted on the mask?

Walking through a fire with 4500 PSI on a hose sounds scary. What would be the advantage? It has been a while, but all the SCBA rigs I have seen use a valve-mounted first stage.

 

[FFPEREZ]

I can’t tell from that photo but it seems very odd that they would run HP through a high-flow hose instead of mounting the first stage directly to the valve. Are you sure the cylinder connection at the valve doesn’t drop to an intermediate pressure (500-1000 PSI???) before entering another pressure reducing regulator, and finally the demand regulator mounted on the mask?

Walking through a fire with 4500 PSI on a hose sounds scary. What would be the advantage? It has been a while, but all the SCBA rigs I have seen use a valve-mounted first stage.

The pic is a newer style pack than the ones I currently wear, it has a quick fill mounted near the valve.

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I Have always been told it was the high pressure hose. Most have a 90 degree fitting an a hose up. Some have a low air bell mounted in that area. Honestly I don't know how high of pressure goes through the hose.

 

[tsunamimike]

your tank can be upside down. i'm a commercial diver and our bail out bottles are usually upside down like that.