I have no idea... I even put a smilie in there to indicate I was kidding.
Yah, I still answered that. You're right. As the tension between source and destination decreases, transfer diminishes. It's standard physics and just as true for decompression. There are a few work arounds that help ameliorate the issue, but it's still there. It's also true when filling from a cascade.
Roger that and thanks to all for your input and experiences shared...appreciated.I have no idea... I even put a smilie in there to indicate I was kidding.
You're right. As the tension between source and destination decreases, transfer diminishes. It's standard physics and just as true for decompression. There are a few work arounds that help ameliorate the issue, but it's still there. It's also true when filling from a cascade.
I respect both @tbone1004 and @Wookie to pieces. Even then, we don't fully agree on this and I imagine someone will come after and muddy the waters even more. We all have slightly different perspectives. Wookie works with large commercial compressors, and possibly with Government compressors which can be hyuge. TBone and I have dealt with commercial and smaller compressors, and I know that most on this Board are utilizing personal compressors. They do not act in the same manner. In addition, I worked in UF's Chemistry Department where I had to deal with both pressure and vacuum vessels on a daily basis. I have STP tattooed on my brain somewhere. All of us are right, depending on the equipment you're using.
Indeed my degrees were BioOcn and my Bride Phd PhyOcn...so STP was more relevant for her than me...but as DSO I oversaw a Posiedon compressor in our dive locker...14+cfm as I remember...filled six 80cfs at once...so the world of small portable compressor is a new realm for me....enjoying the learning curve. Lots of experiential knowledge on the forum to learn from!
Perhaps on board a dive boat...but at $13 K Haskel Booster for Diving Applications my portable compressor will have to do....my PRV is at 3,300psi so not a real need for my application...and I am diligently trying to keep my compressor "KISS"...So I am probably dating myself......... but every compressor system can benefit from a Haskel...
now that that Usun boosters are out, there is not a lot of justification for a branded Haskel anymore. I sold off all of my pneumatic boosters and own a pair of Masterline electric boosters which I would argue are more valuable to me than the compressors but that's largely from a CCR and technical diving perspective.
Alas...I am caught...my background in science has me in a bind...I always want to know the "why" of a process and I noticed on the first use of my small compressor that there was apparently a slower flow rate close to terminal pressure of 3K psi....I do not need psi above 3K and the fill rate is fine....just needed to see if the perceived cause and effect was real....no need for over 60 mins at depth and not doing decom dives so more gas [higher psi] is a moot point and only something that would cost more, be heavier and still have a lot of gas left over at end of dives...no booster and always yokes [under 3.5K psi]...with occasional double hose use..
I quit over-head dives decades ago so I will leave that to the tech divers....
engineer here, so I fully understand. One of the biggest factors is going to be the Z-factor for non-linear compressibility. This is not often talked about outside of this forum and some other unique groups in technical diving, but it is very real. @DiveGearExpress thankfully did a good reference article about it which saves me from having to explain a lot about it.Alas...I am caught...my background in science has me in a bind...I always want to know the "why" of a process and I noticed on the first use of my small compressor that there was apparently a slower flow rate close to terminal pressure of 3K psi....I do not need psi above 3K and the fill rate is fine....just needed to see if the perceived cause and effect was real....no need for over 60 mins at depth and not doing decom dives so more gas [higher psi] is a moot point and only something that would cost more, be heavier and still have a lot of gas left over at end of dives...no booster and always yokes [under 3.5K psi]...with occasional double hose use..
www.divegearexpress.com
Understood and well stated. Temp is always the gorilla in the "room" [tank...]. Another flow rate changer for me was how often and how much I opened my condensate drain....as this was my first use, I was a tad bit over zealous...and that slowed the bottle charging...engineer here, so I fully understand. One of the biggest factors is going to be the Z-factor for non-linear compressibility. This is not often talked about outside of this forum and some other unique groups in technical diving, but it is very real. @DiveGearExpress thankfully did a good reference article about it which saves me from having to explain a lot about it.
There is other factors going on with the increased amount of work required as the resistance to flow increases at higher pressure, increased heat that reduces gas density, etc etc. When you're working on large systems with big cascades like @Wookie is used to, or the one that @The Chairman and I are working on installing you will rarely notice it. Primary reason being that the pump will get heat soaked fairly quickly and is running under relatively constant load for long periods of time so as the psi/min goes down you aren't really going to notice it since the net system change is incredibly slow. Some of the banks that I'm used to take multiple hours to refill and you're also usually doing it while filling scuba tanks so you really aren't paying attention to the flow rates. This is in stark contrast to a personal use compressor that is directly filling a scuba tank in <30mins where you do actually start to notice the psi/min differences during a fill session.Z Factors for SCUBA | Dive Gear Express®
Cylinder volume is defined by the internal dimensions of the tank, and normally measured in cubic inches or liters of water. Free capacity is ...
Oh, and one other factor that is going to be very different on a personal pump vs. a cascade system. When you are filling from a cascade system your fill rate to the tank is usually higher than the fill rate from the compressor, this causes the tank to get quite warm fairly quickly. The compressor however is filling into a massive heat sink that has relatively low psi/min changes so the banks act as a massive heat sink. When you are direct filling from a small pump you actually have adiabatic cooling after the PMV when you are filling at lower pressure than the PMV setpoint and because the flow rate is relatively low you then have less heating in the tank. Once you get above the PMV pressure you are filling with hot gas into a hot tank. All this to say there are a LOT of thermodynamics going on in these systems that will ultimately affect your net flow rate and your pressure drop after temperature has equalized and you are going to notice that more from a direct fill system than you would in a cascade which doesn't usually settle nearly as much from filling.
