The only time I've brought a tank that low was feet depth six feet from shore.
That was only because the tank needed hydro.
That was only because the tank needed hydro.
Bad scuba advice you've received
- Thread starter stretchthepenn
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The end dive 500 psi reserve pressure rule has been discussed many times
Ending a dive with 500 psi/35 bar is different using various cylinders. With an AL80, that is 12.9 cu ft/365 l.
Obviously, your average or emergency gas consumption (RMV) will dictate the amount of gas needed for different activities. For a normal ascent from 60 ft with a 3 min safety stop at my average RMV, I need about 3 cu ft/116 psi from an AL80. For an emergency at 130 ft, a minute at the bottom, a normal ascent and a 3 min safety stop at twice my normal RMV, I need about 16 cu ft/620 psi from an AL80 (or a 19 cu ft pony)
Much of my diving is solo drift in SE FL. As I always have free access to the surface, I fairly frequently will end a dive with less than 500 psi in my AL80 if I am not limited by time. I do carry an AL19 pony. When diving in Bonaire with no real time or NDL limit, I will frequently dive my cylinder down before exiting to the shore. There are other examples where the suggested reserve pressure may not be necessary.
Ending a dive with 500 psi/35 bar is different using various cylinders. With an AL80, that is 12.9 cu ft/365 l.
Obviously, your average or emergency gas consumption (RMV) will dictate the amount of gas needed for different activities. For a normal ascent from 60 ft with a 3 min safety stop at my average RMV, I need about 3 cu ft/116 psi from an AL80. For an emergency at 130 ft, a minute at the bottom, a normal ascent and a 3 min safety stop at twice my normal RMV, I need about 16 cu ft/620 psi from an AL80 (or a 19 cu ft pony)
Much of my diving is solo drift in SE FL. As I always have free access to the surface, I fairly frequently will end a dive with less than 500 psi in my AL80 if I am not limited by time. I do carry an AL19 pony. When diving in Bonaire with no real time or NDL limit, I will frequently dive my cylinder down before exiting to the shore. There are other examples where the suggested reserve pressure may not be necessary.
We should be planning our minimum bottom gas with a realistic idea of how much we would use to complete an air sharing ascent from our deepest depth
Most spgs lose their accuracy under 500psi from slop in the mechanism inside, so even if your min gas comes in below 500 it’s prudent to begin your ascent at 500
Most spgs lose their accuracy under 500psi from slop in the mechanism inside, so even if your min gas comes in below 500 it’s prudent to begin your ascent at 500
I'm pretty sure that 500 PSI rule of thumb was developed for operators taking large numbers of tourists to warm water reefs using rental AL80s.
I would guess that most people who dive with their own tanks of varying size (as above) probably have enough diving experience and/or understanding to realize that the rule is to surface with a somewhat arbitrary but reasonable reserve to accommodate gear failures, injuries on the surface, entanglement, delays, etc...
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Yes, I would hope that you are right
The issue with 500psi back on the boat is that you can't make a decision based off the information. You need to know what PSI to start your ascent at that is something you can make a decision off of. Otherwise you're just guessing. Do I need to leave at 1500psi to be back on the boat at 500, or do I need to leave at 600...
johndiver999
Contributor
Mechanical gauge accuracy is not as precise as you think. Check out the info at the bottom of DGX page:
Pressure Gauges (SPG)
Submersible Pressure Gauges (SPGs) and Instrument Consoles
www.divegearexpress.com
TL;DR mechanical gauges are not as accurate close to empty and full - the most accurate reading will be in the middle. This is not a defect but a side effect of the mechanism used.
go diving in Koh Tao.
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