Straggler Dave
Registered
The air coming out of the reg isn't going to be at ambient pressure, as it's shooting out so fast. I'd say the flow rate would be proportional to IP. So it'd only be 30% or so faster at 30m.
:doctor:
Free flow at depth?
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:doctor:
you would have to do the math but I think the flow would be less (but not appreciably less) due a smaller delta P between the compressed air in the tank and the ambient pressure.
Flow rate is a function of flow resistance (head) and delta P (difference in pressure)
Both on the surface and at depth the flow resistace of the freeflowing regulator system will be the same BUT the Delta P will be less ===> it will take longer to drain at depth. I do not think this will be appreciable though since you are talking about a small value relative to your tank pressure.
That said, you better get to where you can do and emergency swimming ascent. If this happened in cold water I would be concerned with a freeze up also.. If that happens all bets are off.
Flow rate is a function of flow resistance (head) and delta P (difference in pressure)
Both on the surface and at depth the flow resistace of the freeflowing regulator system will be the same BUT the Delta P will be less ===> it will take longer to drain at depth. I do not think this will be appreciable though since you are talking about a small value relative to your tank pressure.
That said, you better get to where you can do and emergency swimming ascent. If this happened in cold water I would be concerned with a freeze up also.. If that happens all bets are off.
captain
Contributor
What's the point of this thread? Why would anyone hold the purge button down continously? If the regulator free flows on its own it's time to get to the surface.
Captain
Captain
norcaldiver
Guest
Because some of us are interested in the physics of whether the flow would be faster or slower depending on depth.
norcaldiver
Guest
SO now this is really buging me. I understand the resistance issue. I understand that compression due to presure also.
I'm thinking that the air is at 3000psi in the tank. That doesn't change until it's out of the tank. Because the tank volume doesn't "really" change at depth due to the tank strength, the air doesn't become MORE compressed inside the tank. Am I right? So wouldnt' that leave just the resistance?
You can't think "balloon" science here because the water presure istn' pushing the air out of the tank like it would a balloon.
I'm thinking that the air is at 3000psi in the tank. That doesn't change until it's out of the tank. Because the tank volume doesn't "really" change at depth due to the tank strength, the air doesn't become MORE compressed inside the tank. Am I right? So wouldnt' that leave just the resistance?
You can't think "balloon" science here because the water presure istn' pushing the air out of the tank like it would a balloon.
it is not a resistance (head loss) issue.
The resistance is the regulator system as a whole (which includes the tank valve regulator and hoses). Last I checked the head loss in this system (resistance) will be consistant gegardless of location (I am disregarding the variation on the hose due to external pressure).
It is the difference in pressure that will determine the flowrate and hence the time it take to drain at depth.
on the surface the difference in pressure is 3000psi in the tank and 14.7 psi outside or 2985.3psi
at depth (lets say 99fsw to make it easy) the difference is 3000psi in the tank and 58.5psi external or 2941.2 psi.
You can liken the difference in pressure to voltage and the requlator system as being a common resistor. A higher voltage with the same resistance will have a higher current (flowrate).
And one of the previous posts is correct.... Air will flow until the diffference in pressure is 0psi internal and external or in the examaple above 58.5psi as you go up the external pressure will decrease (14.7 psi per 33fsw) so the air in the tank will flow out (this is why you keep your regulator in your mouth during an emergence swimming ascent)
moral of the story.... who cares get to the surface!
Pete
The resistance is the regulator system as a whole (which includes the tank valve regulator and hoses). Last I checked the head loss in this system (resistance) will be consistant gegardless of location (I am disregarding the variation on the hose due to external pressure).
It is the difference in pressure that will determine the flowrate and hence the time it take to drain at depth.
on the surface the difference in pressure is 3000psi in the tank and 14.7 psi outside or 2985.3psi
at depth (lets say 99fsw to make it easy) the difference is 3000psi in the tank and 58.5psi external or 2941.2 psi.
You can liken the difference in pressure to voltage and the requlator system as being a common resistor. A higher voltage with the same resistance will have a higher current (flowrate).
And one of the previous posts is correct.... Air will flow until the diffference in pressure is 0psi internal and external or in the examaple above 58.5psi as you go up the external pressure will decrease (14.7 psi per 33fsw) so the air in the tank will flow out (this is why you keep your regulator in your mouth during an emergence swimming ascent)
moral of the story.... who cares get to the surface!
Pete
Straggler Dave
Registered
But the air effectively comes from the hose, not the tank. And the 1st stage will keep the IP in the hose at a constant pressure above ambient.
the flow rate of a reg depends on the intermediate pressure of the first stage and it's effect on the volume of air that can go through the reg at a given time. Lowering the IP of a first stage will reduce the maximum flow rate, increasing it will increase the maxiumum flow rate.
At 132 ft you would have about 59 psi of water pressure. This would mean the intermediate presure in the first stage would increase from 140 psi at the surface to 197 psi due t the ambient pressure at 132 ft. So the the flow rate would not be 4 times as much as at the surface but rather only 1.4 times as much as at the surface.
In most regs the second stage is the limiting factor and will run from 30 cu ft/min for a low end second stage to 60-70 cu ft/min for a high performance reg.
My D400 second stage has a flow rate of about 65 cu ft/min and assuming you get 1.4 times this amount free flowing at 132 ft, you are talking 91 cu ft per minute which is well within the flow capacity of the Mk 25 first stage which is 150+ cu ft/min.
The bad news is that this means a free flow at 130 ft could empty a full steel 72 in about 45 seconds with a high performance reg.
The first free flow I ever had was at 30ft with a low performing Mk 3 reg and it took maybe 3 minutes to dump the contents of the tank. The next and last free flow I had was with a MK 15 D400 at 140 ft. Unfortunately I based my estimate on how long it would take on my prior experience with free flows and consequently finished freeing the anchor and delayed switching to a pony. I was surprised to have things suddenly run out of air after only 30 seconds or so.
At extreme depths, (greater than 600 ft. ) the density of the gas should become a limiting factor as the density exceeds the capacity of the internal passages to efficiently move the "thicker" gas.
At 132 ft you would have about 59 psi of water pressure. This would mean the intermediate presure in the first stage would increase from 140 psi at the surface to 197 psi due t the ambient pressure at 132 ft. So the the flow rate would not be 4 times as much as at the surface but rather only 1.4 times as much as at the surface.
In most regs the second stage is the limiting factor and will run from 30 cu ft/min for a low end second stage to 60-70 cu ft/min for a high performance reg.
My D400 second stage has a flow rate of about 65 cu ft/min and assuming you get 1.4 times this amount free flowing at 132 ft, you are talking 91 cu ft per minute which is well within the flow capacity of the Mk 25 first stage which is 150+ cu ft/min.
The bad news is that this means a free flow at 130 ft could empty a full steel 72 in about 45 seconds with a high performance reg.
The first free flow I ever had was at 30ft with a low performing Mk 3 reg and it took maybe 3 minutes to dump the contents of the tank. The next and last free flow I had was with a MK 15 D400 at 140 ft. Unfortunately I based my estimate on how long it would take on my prior experience with free flows and consequently finished freeing the anchor and delayed switching to a pony. I was surprised to have things suddenly run out of air after only 30 seconds or so.
At extreme depths, (greater than 600 ft. ) the density of the gas should become a limiting factor as the density exceeds the capacity of the internal passages to efficiently move the "thicker" gas.
Could be a bit off here; but I think a balanced regulator will keep it's internal pressure ratio to ambient pressure pretty even until you start going really deep. At those depths the "drag" that divers feel is the thickness (density) of the gas itself. At 4 ATA the gas would be 4x as dense (not that this is really deep
)
A free flowing regulator should flow just as much gas at depth as it would at the surface, maybe just a tiny bit more or less based on some of the physics presented here. For the sake or keeping it very simple, you could probably assume that you would blow through 4x as much gas free-flowing at 99fsw as you would at the surface due to the gas density on a balanced regulator.
Should this happen I'm with the rest, grab your buddy and get the hell out of there.
A free flowing regulator should flow just as much gas at depth as it would at the surface, maybe just a tiny bit more or less based on some of the physics presented here. For the sake or keeping it very simple, you could probably assume that you would blow through 4x as much gas free-flowing at 99fsw as you would at the surface due to the gas density on a balanced regulator.
Should this happen I'm with the rest, grab your buddy and get the hell out of there.
Charlie99
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Which goes back to the question of whether the flow limitation is primarily the 2nd stage or the 1st stage. If the limiting factor is the 1st stage, the IP is NOT at a constant pressure above ambient.
There was a post in another thread about how you can't really breathe off the octo very easily when there is a freeflow on the primary, because the IP goes very low.
I'll do some tests next time I'm in the water, but right now it looks like my next time wet won't be until late August.
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