So how do you know or calculate the effective capacity of a tank? Is there a chart somewhere or a way to calculate it? At 5:30 you stated that an AL 80's effective capacity is 53 CF. I heard they run smaller than the stated capacity in general something like 67 cf if I recall correctly. However being a new diver it would be good to know. Especially as I learn to determine what tanks to get. Based on the advice of area divers I got a pair of Steel LP 85s. At the low side they should be filled to 2600 but it will likely be filled to 3000-3200 psi.
There should be a stamp on the side telling you its nominal capacity. In the US if it's an 80 cuft tank that means that at the max fill pressure (3000psi for Brian's example) the tank will at 3000psi contain what would be 80cuft of air at normal atmospheric pressure. Brian's figure of 53cuft comes from the rule of thirds. 53 is 2/3 of 80. You should plan to use only up to 2/3 of your gas on the dive; you will still have 27cuft/1000psi left in the tank and you can breathe it. But it's your safety margin in case you have to, for instance, share your air with a buddy on the way up. By the way, if a tank is rated at 3000psi it should not be filled to 3200. This is especially important for aluminum tanks, but for Al and steel regular over-pressure will in the long term lead to stress cracking and eventually failure. Steel cylinders are often rated higher, typically 3360psi, but you need to check the stamp on the side to check. A responsible fill station will not give you more than this value! Hope this helps, and safe diving!
Hello @MysticalDragon73, the easiest way to calculate the usable gas is as follows. Whatever you cylinder capacity is, in this case an 80cf cylinder, you take that number and divide it by 3. This will give you the individual 3rd of the cylinder. Then simply multiply that by 2 and you have the workable gas in the cylinder. Example: 80cf divided by 3 is 26 cf. Then 26 multiplied by 2 is 53 cf. 53 cf is the workable gas and 26 cf is the reserve. You can do this with any cylinder as long as you know the volume it holds. You can also do the same math based on pressure to see what your run time will be (in real time) while underwater. Hope this helps.
"GASP" Bryan just mentioned me! I can just hang up my spurs now. Lol, thanks man. I did just post a video on how to calculate SAC rate, and in the comments I also got this same question a lot, and it is hard to explain, typing. So, sweet video. If I was to sum this up, SAC is real time data on how their air consuption is going, and RMV is used when needing to find out how much gas volume is need when planning a dive. Of course it makes sense. We have our DM students (and anyone else interested in improving their air consumption) calculate their SAC rate with specific parameters, at the beginning of a course, then again in the end to see how they improve. I'm not personally a tech instructor so don't use RMV much, except when doing my own tech dives and seeing how much gas to bring on deco dives. Anyway, thanks for answering my question, I could keep those coming all day. I look forward to your mirror arriving in Philippines!
Glad you enjoyed the video @DecoLounge-scuba. I just checked tracking on the mirror, and it says it just passed through customs in the Philippines. I can email you a tracking number.
I'm afraid SAC is not real-time data and RMV is not planning data. Arguably the other way around is more useful. RMV is the physical volume that cycles through your lungs (as the name implies). SAC is that value adjusted for surface pressure. So if your SAC is 20L/min and you are at 20m, then your RMV is 60L/min. Whether you convert that into pressures from your cylinder to track real-time usage, or you keep it this way to plan for gas volumes needed, is irrelevant.
@@DecoLounge-scuba It's not what he said in the video ;). He said that SAC is pressure per minute, while RMV is volume per minute. He also claimed that RMV is a surface measurement while it is a depth adjusted value. H even made a point of not using RMV because it is a volume measurement in cuft or L, but instead to use SAC because it is a pressure measurement so we don't need to do any math. This is plainly incorrect. If I use SAC even as pressure per minute number, I still need to do math to adjust for the depth. There is a massive confusion around the terminology in the video. Everything he said about how to use the numbers in the different units is fine. But the terminology of what these different numbers are, is incorrect and incredibly confusing. Point and case, your "If I was to sum this up, ..." comment shows clearly the confusion. If Bryan had explained it clearly and correctly, you would know that your summation of the video is not correct.
Feeling so smug working in metric here, because we can do math in our heads if it's the ten times table! RMV and SAC are both used here in UK but SAC seems to be used as a coverall for both. My Multideco App and my computers use and work out SAC in litres/min, my buddy's computers show SAC in Bar/min. Like you say you need both numbers: SAC in volume/min for gas planning and pressure/min for that mental arithmetic on the dive. Now I know my SAC I find a ballpark Bar or psi/min for approx depth is always nice to have in the back of my mind to let me run a mental how-goes-it.
So on my mares quad air when i read 0.59 CF on the down right corner of the screen and i am 33 feet (pressing the down button on the right i think). Does this mean that my RMV at 33 feet is actually 0.59 CF ? (hopefully it s clear) No wear in the user guide of the quad it explain this
@@LakeHickoryScuba Oh that's great. It just begs the question why your explanation treads very closely to the second common wrong explanation Harry mentions. Meanwhile the main important aspect, namely RMV being SAC adjusted for depth, or if you prefer SAC being RMV adjusted for surface pressure, is somewhat absent from your explanation. Instead you talk about SAC being an umbrella term and that you have the different numbers that are both necessary. Don't get me wrong, both numbers that you refer to are relevant, but you are not actually explaining the difference between RMV and SAC. In fact, Deco lounge-scuba is trying to sum it up here in the comments and is getting it awfully wrong, yet your reply to their comment isn't picking that up.
So the easiest way to explain the difference between SAC and RMV is this. SAC otherwise known as Surface Air Consumption (which can be calculated in BAR or PSI, and can also be calculated in Cubic Footage or Liter for cylinder referencing, hence, why its an umbrella term) is nothing more than the measurement of how much gas is breathed per minute at the surface in a measurable term (bar/psi, or cubic feet/liter). Measurable term meaning we have a physical gauge that we can monitor and see in real time. RMV which is Respiratory Minute Volume which is another way of saying Tidal Volume which we use in the Medical Industry instead of RMV. This is the amount of air that moves in and out of the lungs during each breath (coincidentally, is also our lung capacity), still measured at the surface. This number is non measurable on the fly as we do not typically as scuba divers carry a specialized gauge with us to monitor the Tidal Volume of gas moving in and out of lungs at depth / per breath. Another fun fact for you, your SAC rate can change by simply changing one variable, however, a diver's RMV rate will never change, as its the physical amount of gas (measured in volume) that it takes to fill up your lungs at the surface. We don't have the option to physically change our lung capacity per breath, as our lungs are the same size at all times. This causes a lot of confusion with divers as the math dictates otherwise at depth, and we are all taught that the deeper we go the more we breathe. But the formulas we use rectify this as we convert depth to ATA thus bringing everything back to the surface. So as a quick recap, SAC is an umbrella term for a measurable number indicating how much gas we are breathing at the surface per breath based on several variables, and RMV is nothing more the your lungs physical capacity to hold air, measured again at the surface. Hope this helps to clear up your confusion.
@@LakeHickoryScuba You see, what you are saying is inherently confused. I'm ok with you saying that SAC is an umbrella term because you can measure it in different units. OK. I can see that argument. But then it starts getting confused. "RMV which is Respiratory Minute Volume which is another way of saying Tidal Volume" - wrong. The "tidal volume" is the amount that moves in and out of your lungs over a single breath. RMV is the amount over a minute. Most people do not make a single breath per minute. "This is the amount of air that moves in and out of the lungs during each breath (coincidentally, is also our lung capacity), still measured at the surface." - Just because the medical profession measures it at the surface because that is where we live, doesn't mean that the volume isn't to be adjusted for pressure in a pressurized environment. Also the tidal volume is not the lung capacity. The avg human lung capacity is around 6L. The tidal volume is usually around 0.5L. We rarely cycle our full lungs to breathe. You are implicitly claiming here that you fully exhale and fully inhale on every breath, i.e., you couldn't physically get any more gas in or out at the bottom/top of your breathing cycle. "Another fun fact for you, your SAC rate can change by simply changing one variable, however, a diver's RMV rate will never change, as its the physical amount of gas (measured in volume) that it takes to fill up your lungs at the surface." - wrong. If you breathe twice as fast with the same tidal range, you double both you SAC and your RMV. If you breathe at the same rate but you double your tidal volume (not even difficult to achieve), you double both your SAC and your RMV. RMV is not lung capacity. It is the tidal range of each breath multiplied by the number of breaths you take per minute. There are multiple variables here that can be adjusted. "This causes a lot of confusion with divers as the math dictates otherwise at depth, and we are all taught that the deeper we go the more we breathe." I've never told a student that they breathe more when they go deeper. However, they consume more gas from the cylinder when they go deeper because they physically cycle more gas through their lungs due to the pressure.
My next question: i just finished ANDP, and im not sure i really understand how to determine what my gradient factor is. I want to fully understand every topic before i do extended range
@@DecoLounge-scuba I will be happy to make a video on that very topic for you. Until then send me an email and I will give you some pointers on how to choose the appropriate Gradient factor for you.
Bryan thank you for all of your help to help us be a safer and better divers
Glad you like our videos @GunnerPierce70.
So how do you know or calculate the effective capacity of a tank? Is there a chart somewhere or a way to calculate it?
At 5:30 you stated that an AL 80's effective capacity is 53 CF. I heard they run smaller than the stated capacity in general something like 67 cf if I recall correctly. However being a new diver it would be good to know. Especially as I learn to determine what tanks to get.
Based on the advice of area divers I got a pair of Steel LP 85s. At the low side they should be filled to 2600 but it will likely be filled to 3000-3200 psi.
There should be a stamp on the side telling you its nominal capacity. In the US if it's an 80 cuft tank that means that at the max fill pressure (3000psi for Brian's example) the tank will at 3000psi contain what would be 80cuft of air at normal atmospheric pressure. Brian's figure of 53cuft comes from the rule of thirds. 53 is 2/3 of 80. You should plan to use only up to 2/3 of your gas on the dive; you will still have 27cuft/1000psi left in the tank and you can breathe it. But it's your safety margin in case you have to, for instance, share your air with a buddy on the way up.
By the way, if a tank is rated at 3000psi it should not be filled to 3200. This is especially important for aluminum tanks, but for Al and steel regular over-pressure will in the long term lead to stress cracking and eventually failure. Steel cylinders are often rated higher, typically 3360psi, but you need to check the stamp on the side to check. A responsible fill station will not give you more than this value! Hope this helps, and safe diving!
Hello @MysticalDragon73, the easiest way to calculate the usable gas is as follows. Whatever you cylinder capacity is, in this case an 80cf cylinder, you take that number and divide it by 3. This will give you the individual 3rd of the cylinder. Then simply multiply that by 2 and you have the workable gas in the cylinder. Example: 80cf divided by 3 is 26 cf. Then 26 multiplied by 2 is 53 cf. 53 cf is the workable gas and 26 cf is the reserve. You can do this with any cylinder as long as you know the volume it holds. You can also do the same math based on pressure to see what your run time will be (in real time) while underwater. Hope this helps.
@@LakeHickoryScuba thanks I appreciate it.
"GASP" Bryan just mentioned me! I can just hang up my spurs now.
Lol, thanks man. I did just post a video on how to calculate SAC rate, and in the comments I also got this same question a lot, and it is hard to explain, typing. So, sweet video.
If I was to sum this up, SAC is real time data on how their air consuption is going, and RMV is used when needing to find out how much gas volume is need when planning a dive.
Of course it makes sense. We have our DM students (and anyone else interested in improving their air consumption) calculate their SAC rate with specific parameters, at the beginning of a course, then again in the end to see how they improve.
I'm not personally a tech instructor so don't use RMV much, except when doing my own tech dives and seeing how much gas to bring on deco dives.
Anyway, thanks for answering my question, I could keep those coming all day. I look forward to your mirror arriving in Philippines!
Glad you enjoyed the video @DecoLounge-scuba. I just checked tracking on the mirror, and it says it just passed through customs in the Philippines. I can email you a tracking number.
I'm afraid SAC is not real-time data and RMV is not planning data. Arguably the other way around is more useful. RMV is the physical volume that cycles through your lungs (as the name implies). SAC is that value adjusted for surface pressure. So if your SAC is 20L/min and you are at 20m, then your RMV is 60L/min. Whether you convert that into pressures from your cylinder to track real-time usage, or you keep it this way to plan for gas volumes needed, is irrelevant.
@tobiashartung856 that's what he said in the video
@@DecoLounge-scuba It's not what he said in the video ;). He said that SAC is pressure per minute, while RMV is volume per minute. He also claimed that RMV is a surface measurement while it is a depth adjusted value. H even made a point of not using RMV because it is a volume measurement in cuft or L, but instead to use SAC because it is a pressure measurement so we don't need to do any math. This is plainly incorrect. If I use SAC even as pressure per minute number, I still need to do math to adjust for the depth. There is a massive confusion around the terminology in the video. Everything he said about how to use the numbers in the different units is fine. But the terminology of what these different numbers are, is incorrect and incredibly confusing. Point and case, your "If I was to sum this up, ..." comment shows clearly the confusion. If Bryan had explained it clearly and correctly, you would know that your summation of the video is not correct.
@tobiashartung856 actually, I'm not incorrect, all I did was sum up what he said. But I know he knows what he's talking about.
Feeling so smug working in metric here, because we can do math in our heads if it's the ten times table! RMV and SAC are both used here in UK but SAC seems to be used as a coverall for both. My Multideco App and my computers use and work out SAC in litres/min, my buddy's computers show SAC in Bar/min. Like you say you need both numbers: SAC in volume/min for gas planning and pressure/min for that mental arithmetic on the dive. Now I know my SAC I find a ballpark Bar or psi/min for approx depth is always nice to have in the back of my mind to let me run a mental how-goes-it.
Hello @timgosling6189, we use both the MultiDeco App and V-Planner. I personally prefer MultiDeco over the other.
@@LakeHickoryScuba Me too.
So on my mares quad air when i read 0.59 CF on the down right corner of the screen and i am 33 feet (pressing the down button on the right i think). Does this mean that my RMV at 33 feet is actually 0.59 CF ? (hopefully it s clear) No wear in the user guide of the quad it explain this
You should watch Cave Diver Harry's video "RMV vs. SAC: What’s the Difference?"
Hello @tobiashartung856, I have seen his video, and have spoke to him several times down in Florida.
@@LakeHickoryScuba Oh that's great. It just begs the question why your explanation treads very closely to the second common wrong explanation Harry mentions. Meanwhile the main important aspect, namely RMV being SAC adjusted for depth, or if you prefer SAC being RMV adjusted for surface pressure, is somewhat absent from your explanation. Instead you talk about SAC being an umbrella term and that you have the different numbers that are both necessary. Don't get me wrong, both numbers that you refer to are relevant, but you are not actually explaining the difference between RMV and SAC. In fact, Deco lounge-scuba is trying to sum it up here in the comments and is getting it awfully wrong, yet your reply to their comment isn't picking that up.
So the easiest way to explain the difference between SAC and RMV is this. SAC otherwise known as Surface Air Consumption (which can be calculated in BAR or PSI, and can also be calculated in Cubic Footage or Liter for cylinder referencing, hence, why its an umbrella term) is nothing more than the measurement of how much gas is breathed per minute at the surface in a measurable term (bar/psi, or cubic feet/liter). Measurable term meaning we have a physical gauge that we can monitor and see in real time. RMV which is Respiratory Minute Volume which is another way of saying Tidal Volume which we use in the Medical Industry instead of RMV. This is the amount of air that moves in and out of the lungs during each breath (coincidentally, is also our lung capacity), still measured at the surface. This number is non measurable on the fly as we do not typically as scuba divers carry a specialized gauge with us to monitor the Tidal Volume of gas moving in and out of lungs at depth / per breath. Another fun fact for you, your SAC rate can change by simply changing one variable, however, a diver's RMV rate will never change, as its the physical amount of gas (measured in volume) that it takes to fill up your lungs at the surface. We don't have the option to physically change our lung capacity per breath, as our lungs are the same size at all times. This causes a lot of confusion with divers as the math dictates otherwise at depth, and we are all taught that the deeper we go the more we breathe. But the formulas we use rectify this as we convert depth to ATA thus bringing everything back to the surface. So as a quick recap, SAC is an umbrella term for a measurable number indicating how much gas we are breathing at the surface per breath based on several variables, and RMV is nothing more the your lungs physical capacity to hold air, measured again at the surface. Hope this helps to clear up your confusion.
@@LakeHickoryScuba You see, what you are saying is inherently confused. I'm ok with you saying that SAC is an umbrella term because you can measure it in different units. OK. I can see that argument. But then it starts getting confused.
"RMV which is Respiratory Minute Volume which is another way of saying Tidal Volume" - wrong. The "tidal volume" is the amount that moves in and out of your lungs over a single breath. RMV is the amount over a minute. Most people do not make a single breath per minute.
"This is the amount of air that moves in and out of the lungs during each breath (coincidentally, is also our lung capacity), still measured at the surface." - Just because the medical profession measures it at the surface because that is where we live, doesn't mean that the volume isn't to be adjusted for pressure in a pressurized environment. Also the tidal volume is not the lung capacity. The avg human lung capacity is around 6L. The tidal volume is usually around 0.5L. We rarely cycle our full lungs to breathe. You are implicitly claiming here that you fully exhale and fully inhale on every breath, i.e., you couldn't physically get any more gas in or out at the bottom/top of your breathing cycle.
"Another fun fact for you, your SAC rate can change by simply changing one variable, however, a diver's RMV rate will never change, as its the physical amount of gas (measured in volume) that it takes to fill up your lungs at the surface." - wrong. If you breathe twice as fast with the same tidal range, you double both you SAC and your RMV. If you breathe at the same rate but you double your tidal volume (not even difficult to achieve), you double both your SAC and your RMV. RMV is not lung capacity. It is the tidal range of each breath multiplied by the number of breaths you take per minute. There are multiple variables here that can be adjusted.
"This causes a lot of confusion with divers as the math dictates otherwise at depth, and we are all taught that the deeper we go the more we breathe." I've never told a student that they breathe more when they go deeper. However, they consume more gas from the cylinder when they go deeper because they physically cycle more gas through their lungs due to the pressure.
@ Looks like you got it all figured out.
My next question: i just finished ANDP, and im not sure i really understand how to determine what my gradient factor is. I want to fully understand every topic before i do extended range
@@DecoLounge-scuba I will be happy to make a video on that very topic for you. Until then send me an email and I will give you some pointers on how to choose the appropriate Gradient factor for you.
@LakeHickoryScuba thanks bud