How A Cascade Tank Filling System Works - Scuba Tech Tips: S11E08

Divers asked why the store compressor is not used to fill tanks directly? Alec shows how dive shops can fill lots of tanks quickly without running an expensive and loud compressor.
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[@martinholloway7694]

I can’t overstate just how much I’ve learned from your videos. Thank you for the engaging content. Great stuff.

[@AlecPeirceScuba_SeaHunter]

Glad to help. Lots of big and small things to learn about scuba, including its early years. Thanks for watching. A

[@gee4526]

Thank you Alec. I have often wondered how they fill tanks all day and never seem to run a compressor. Now I know how it works. Gosh I love education.

[@AlecPeirceScuba_SeaHunter]

Glad to help you become a smarter diver.

[@garyviveiros2557]

Thanks, Alec. I was going to bypass the tutorial because I don't scuba, but I felt God telling me that the principle is going to be important, so listen to it. I understand your logic. Can't wait to see where it gets used elsewhere!

[@AlecPeirceScuba_SeaHunter]

Excellent! A

[@Fernando_Woolybooger]

Why couldn't all of my teachers and college professors teach as well as Alec. You sir are awesome! And I thank you.

[@AlecPeirceScuba_SeaHunter]

You rock!

[@user-hg3cp2bs4k]

Hi Alec, Such an excellent explanation that I'm trying to understand about cascaded air filling systems... Thanks a Lot!!!! I got an well described answer after searching for long time...!!!

[@AlecPeirceScuba_SeaHunter]

Glad it was helpful! Lots more to learn if you can stand my humour. A

[@nobarakugisaki356]

Thank you Alec , I passed this video to my friend who owns a Dive centre He was looking for a setup like this since lockdown happened, this decision was delayed as he was short of finance Thanks to Alec, now he totally changed his mind, because 1. With the same investment, of buying all the huge tanks, he would rather buy scuba diving tanks, as its 2. going to save a lot of space 3. Less complicated as compared to the setup needed 4. And will work with his normal equipment without any technical training 5. And his compressor will also not be affected 6. Tank you very much Alec

[@AlecPeirceScuba_SeaHunter]

Glad this was a help. We had lots of fun with Kris at Simcoe Dive including dropping tanks on his floor (look up that video). A

[@Ryaa680]

So glad you're still making videos Alec.

[@AlecPeirceScuba_SeaHunter]

Me too!

[@Will-ol9lp]

Great video Alec. That’s what we use in the medical system to refill our oxygen tanks

[@AlecPeirceScuba_SeaHunter]

So you are one of the few who understands that this does work!

[@donaldotsig6818]

Thanks Alex for all the work you do and all the great videos,i have learned a lot from you .

[@AlecPeirceScuba_SeaHunter]

I appreciate that! Glad to share my knowledge and experiences with the diving world. A

[@foghornleg90]

Perfectly explained, and exactly how it was explained to me back in the 80's when I first saw one of these 'systems.' Thanks...

[@AlecPeirceScuba_SeaHunter]

You are welcome!

[@SherifEgypt]

OMG, it took me full attention to be able to understand this. Thanks for the great info.

[@AlecPeirceScuba_SeaHunter]

You're very welcome!

[@bigfoot1465]

We used a very similar system for the 20 years I was in fire service. In most instances we had 6-8 very large tanks filled to approximately 4500 psi. These were usually mounted on a trailer with a separate station mounted compressor. On a very large fire scene we would tow the trailer and re-fill the air tanks on the scene. If not that many tanks were needed then we would re-fill them back at the station any time of the day without having to run the compressor. We would normally fill the main cylinders as needed. We called it a cascade system. Later we had a rescue truck with tanks mounted permanently in it that could be driven to the scene. Also in this way not every station needed a compressor but could be towed or driven to a central station for re-filling! This cascade system works great!

[@AlecPeirceScuba_SeaHunter]

Thanks Mr Bigfoot14 for sharing this and that these systems are everywhere, not just for divers.

[@toriless]

@@AlecPeirceScuba_SeaHunter Yeah, I never thought about the need for firefighting gear.

[@mpoisot]

I'm curious, how is compressed air used for firefighting?

[@bigfoot1465]

It’s used for breathing air in all firefighting airpacks.

[@mpoisot]

@@bigfoot1465 Ahh of course

[@DigginwithSeven]

Very well explained. Thanks for sharing

[@AlecPeirceScuba_SeaHunter]

Glad it was helpful!

[@haisambelal1]

You are amazing , Thanks so much from Egypt

[@AlecPeirceScuba_SeaHunter]

You are very welcome and I loved diving the Red Sea.

[@NoWorriesNoHurries]

Perfect 30 second summary at the end @ 7:54! Thanks Alec your videos are great!

[@AlecPeirceScuba_SeaHunter]

Glad you like them! A

[@jamesperez2294]

Thank you this is the exact info I was looking for.

[@AlecPeirceScuba_SeaHunter]

Glad it was helpful!

[@Engineer9736]

Here in The Netherlands and Belgium you have a lot of automatic bottle filling stations. Just hook up your tank, toss a coin in the machine and it fills right up to 200 bar / 3000 psi. I guess they have just 1 big bank of 4000psi then? I can't imagine that they go through some automatic switching system or so.

[@AlecPeirceScuba_SeaHunter]

Did not know there were such devices. Rules in Canada do not allow filling without a qualified operator. Another good idea that may expand to North America some day. A

[@diveinstructordaniel1095]

Very interesting, thanks Alec 🤙

[@AlecPeirceScuba_SeaHunter]

Glad you liked it!

[@sergiollag1]

Fascinating!. I didn't know how that works

[@AlecPeirceScuba_SeaHunter]

Be ready to share it at the next dive club meeting.

[@dailyshorts4742]

awesome video

[@AlecPeirceScuba_SeaHunter]

Glad you enjoyed it

[@JohnSmith-ed1sr]

Thanks for the videos Alex! Please keep doing great stuff. I watch your stuff every time it comes out!

[@AlecPeirceScuba_SeaHunter]

Glad you like them John.

[@lanceorlando5657]

i dont mean to be off topic but does anyone know of a trick to get back into an instagram account?? I was stupid forgot the login password. I love any tips you can give me

[@apolloali1356]

@Lance Orlando instablaster ;)

[@lanceorlando5657]

@Apollo Ali Thanks for your reply. I got to the site through google and Im waiting for the hacking stuff atm. I see it takes quite some time so I will get back to you later with my results.

[@lanceorlando5657]

@Apollo Ali it worked and I finally got access to my account again. Im so happy:D Thank you so much, you saved my account!

[@Makdiver]

Thanks again.. Love your vid..

[@AlecPeirceScuba_SeaHunter]

Glad you like them.

[@kzyt87]

thanks good to learn

[@AlecPeirceScuba_SeaHunter]

Glad it was helpful!

[@pooialalbakhsh7277]

great mate!!!

[@AlecPeirceScuba_SeaHunter]

Thank you! Cheers!

[@TheVinny360]

That is a heck of a set up man that’s pretty awesome 😎

[@AlecPeirceScuba_SeaHunter]

It sure is. Chris at Simcoe Diving also does hydro testing on site.

[@TheVinny360]

Alec Peirce Scuba I bought a new Catalina tank is it a good idea to have it inspected it has had no pressure in it for awhile an I’m waiting to go get certified I passed my PADI elearning part of the course time to get open certification 😁👌

[@uncatila]

great. I learned something

[@AlecPeirceScuba_SeaHunter]

Hurray. Much more to learn then share at the next dive club meeting. A

[@martinavrdoljak2923]

You are best.

[@AlecPeirceScuba_SeaHunter]

Much appreciated Martina. Thanks for watching.

[@timbartlett4898]

Thank you sir! Im the guy that delivers all of the liquid O2 and He ..Liquid Hydrogen and compressed to welding shops ..hospitals ..power plants it’s amazing how many businesses run on cryogenics...love your podcasts sir..like a walking talking U.S.Navy Dive Manual

[@AlecPeirceScuba_SeaHunter]

Thanks Tim. Most folks don't realize the variety of gases and tanks that you guys supply. Did you note the 'Aviators Breathing Oxygen' white tanks in this? Simcoe Diving does a lot of fills for EMS and divers. When I stared diving in 1958, we referenced the USN dive manual and it is still a great document to read today.

[@TJForehand]

This could have been explained in about 60 seconds, but I can tell you enjoy your setup and job, and storytelling...so I watched through to the end. Cheers.

[@AlecPeirceScuba_SeaHunter]

Maybe, but 60 seconds does not allow viewers to remember much, get a complete picture or enjoy my fascinating explanations.

[@zaf88]

i make a habit of not trusting anyone in life. something about you alec, i have to trust you

[@AlecPeirceScuba_SeaHunter]

Thank you for the trust. Just giving my best to divers everywhere who need tips and a laugh. A

[@zaf88]

@@AlecPeirceScuba_SeaHunter all thanks go to you sir. while ive got you, have you done a video on kids gear? ive had my daughter on a reg since she was 3 in the bathtub. then we did the pool on my octo, then as she progressed, the pool on a pony bottle. now she is 10 and we did a dsd last week! i want to get her a decent bcd and reg that can grow with her. have you done a video on gear for kids? if not can you???

[@Schtukas1]

Like Alec said- with this system you can get the compressor to run in the morning, as this is the time when the air is not that humid, instead of having to turn it in during at noon when the air may be hot and extremely humid (saves on filters a fortune)

[@AlecPeirceScuba_SeaHunter]

Right you are Valentin. Most shops have the compressor inlet on the roof away from car exhaust but also much hotter and no shade. Large compressors can be very expensive to maintain but if you have the tanks to fill, it is needed for happy divers.

[@zencat999]

do you have any vid of how to set up a small number of tanks? just got an old bauer mariner and want to see how the tanks are hooked up.

[@AlecPeirceScuba_SeaHunter]

There are consultants who specialize in setting up systems or start discussions on scubaboard.com for the key setup and testing factors.

[@saraha3958]

Hi Alec. That’s a interesting video. Completely off topic what do you think about underwater scooters for diving & what one would you recommend for recreational diving. Cheers Sarah

[@AlecPeirceScuba_SeaHunter]

Scooter are very small, cheap and not too fast but fun if the instructions are followed (re: equalization). However Diver Propulsion Vehicles (DPVs) can be like buying a Ferrari! I'll add this to my idea list for future videos.

[@saraha3958]

@@AlecPeirceScuba_SeaHunter Thànks Alec. I thought they looked fun. I might hire one to start with & await your video with great interest

[@davids7550]

I bet those 420's would make great bells.

[@AlecPeirceScuba_SeaHunter]

Ha you watched that. They would be good bells.

[@haisambelal1]

Dear Alec , kindly i need to know your experience in flying with tanks ..Empty tanks for sure , i heard that i should remove the valve .... is it OK for the tank to keep it exposed like that , and for how long , also should i do any specific maintenance for the tank once arrive? .... another question about tanks also , how to protect the external edge , i'm sure there are many ways starting from the Net covering till painting , what you prefer , what is the best way... i believe we need a video for all of this :) .. thanks in advance.. Haitham

[@AlecPeirceScuba_SeaHunter]

I'm going to assume by tanks you mean small spare-air or pony size in checked luggage as paying for a 80 cu/ft is crazy. If you must take tanks, they have to be empty with the valve off otherwise it will be inspected, unscrewed and probably left off. With the valve off, cover the opening with something strong like plastic wrap and tape around the neck. Each airline and country has specific requirements to check online before hand. At your destination ask the shop filler to check for obvious contaminates (dust, clothing fibres) before filling. Consider renting locally to save a lot of problems.

[@Caderic]

I like the aviation O2. That is an interesting topic. Oxygen on aircraft have to use "Aviation Oxygen" because it has "no" water. That used to be a problem, but today all oxygen system produce "waterless" oxygen, so it doesn't matter. But don't tell the FAA.

[@AlecPeirceScuba_SeaHunter]

I won't Erikk. Very few know about that.

[@xentrix1024]

At last I understand! Thank you. But I still don't get how this minimizes the use of the compressor. In the end, don't you have to compress the same amount of air for a given number of tanks?

[@AlecPeirceScuba_SeaHunter]

True, the compressor has to refill what was used but it comes down to using the compressor in off hours (cooler air, noisy and other factors), and quickly filling multiple tanks, 2-4 at once.

[@MrNomNom24]

Nice, what does your morning compressor routine look like with all those tanks?

[@AlecPeirceScuba_SeaHunter]

When I ran Scuba 2000, near the end of the day I check the bank capacity and how many tanks may need filling the next day. Turn the compressor on to fill each bank to a pre-set limit then it shuts off. Very easy once setup and tested.

[@Nubbe999]

Are the tanks not parallell conected? Would that not leave ypu with more air if you just take air from one bottle at the time. Luke just take air from a low presdure and one high pressure insteed of taking air from 10 low presure and 10 high presure

[@AlecPeirceScuba_SeaHunter]

There are multiple tanks connected to a bank; low (many tanks), medium (several) or high (a few) pressure banks are typical. Filling from one bottle means the closer the tank gets to the fill bottle, the slower and less air it gets. Filling from many means each individual tank goes down much less so more can be filled. Hope this helps and thanks for watching.

[@alaind831]

makes perfect sense - even if you could have the very big tanks at 4500psi (maybe they are also cheaper as LP) you would eventually drop to bellow 3000psi and not get a full fill if you used them all at once, without keeping some HP > 3000psi ones for the last top off to reach full fills...

[@AlecPeirceScuba_SeaHunter]

Yes, there are many ways to setup a cascade system based on daily # of fills, space, cost to run the compressor, fill speed (for the customer not tank) and more. And yes, sometimes we actually had to fill tanks from the compressor for various reasons. Thanks for watching Alain.

[@TauchEin]

Alain Dumesny you have to invest more energy if you do that. Compress to 4500 psi creates bigger amount of heat at the compressor and tanks. Thats bad for overall effeciency. You need more electric energy per tank.

[@toriless]

@@AlecPeirceScuba_SeaHunter My shop use a high PSI of 3000 and then just tops of the 2900+ to 3100+ from the second bank of tanks. It take up less space and tanks but provides enough mass for their use.

[@BurhanMuntasser]

Questions: 1. You only have two banks in this bank system? Typically, the bank systems I have seen have 3 - 4 banks. 2. Why fill one bank to a lower pressure at the beginning? Why not fill all of the banks to the highest pressure possible (up to their rated pressure)? 3. When you run your compressor, do you fill all of the banks in the system at the same time or do you fill one bank and then the other?

[@AlecPeirceScuba_SeaHunter]

Lots of questions so #1; 3 can be typical but remember the greatest psi change is from empty (or close to it) to around 2,500 psi. That takes a lot of volume of air, not so much higher pressure which is why the Simcoe Diving setup has 2. Also Simcoe Diving fills a lot of firefighter tanks (smaller) and other none diving tanks so this setup works great for their customers. #2 Thats the logic of the cascade system, a big fill to 2500 then a small fill to 3100, cooling off to 3000. #3 One bank at a time. Say you had a lot of tank VIS and hydros. All would have to be filled from zero psi using a lot of your Low Pressure volume. Filling a divers tank usually starts at 750 (if smart) or a little higher so no as much LP is used. Where the HP tanks mostly fill from 2500 to 3100 only. Good questions.

[@toriless]

@@AlecPeirceScuba_SeaHunter My shop seem to like more like 3150 which results in 3000 and since it is usually below 40F on the surface the tanks are often 2800 once in the water a while.

[@jacquespoirier9071]

unless you have two compressors, the compressor will run the same amount of time ?, I can understand if you use a higher volume, lower pressure compressor to fill the low pressure portion of your cascade system and a higher pressure , lower volume compressor to fill the higher pressure portion of the cascade system, to me the net benefit is to be able to fill rapidly a number of thank and operate a smaller compressor for a longer make up time out of the demand peak.

[@AlecPeirceScuba_SeaHunter]

It is a balancing act between time, cost and customer needs that every filler has to decide on. At Scuba 2000 we had 3 banks and the compressor filled the lows first, mid tanks second and HP's last and would last days without the need to top up. Thanks for watching Jacques.

[@toriless]

The total time is the same but you are not constantly stopping and starting it which creates more wear. It wears out more types of parts and ones that are not as easy to make more robust with affect their functionality. It also allows time for the bottles to cool off and for the pressure to stabilize so you get a more reliable fill.

[@matthewhignite]

alec what is the meaning between all of the different smb colors i know that orange is common to use and there is yellow black and pink

[@AlecPeirceScuba_SeaHunter]

There is no 'right' SMB colour so it is a personal choice. Years ago, back in the stone age, there were few colour pics. Today has the new bright green with reflective surfaces. Pick the colour you think would stand out if lost.

[@matthewhignite]

i heard some where that some places that yellow was for emergency

[@toriless]

Mine is yellow on one side and orange on the other. I think it all a matter of visibility. I have one with a built-in light too I got from DAN.

[@fanplant]

i'm still not 100% but that did help a lot. Are the bank to bank to bank setups ever regulated/automated?

[@alaind831]

there are not automated at a local shop (3 gauges banks you manually open/close). I suspect the 4500psi has a pressure limiter set to 3500/3000. My other shop is straight from pump which auto-shuts off when reaching 4000psi, with 3 wips sections pre-set to 2400/3000/3500

[@AlecPeirceScuba_SeaHunter]

Alain's description below is correct but it can get more complicated from there. Watch Tech Tip S08E09 What Is A Fill Station? Will show the 'how' banks are switched.

[@toriless]

Most shops have two limit regulators and two lines and then switch during fills. Often the cascade tanks are in back somewhere near the compressor in the back on the shop. My shop has no auto shutoff, it is all manual. I imagine they have more spare employee time then there is need for the expense of automating it. You can also adjust the final pressure for the season. I summer you are going to have a higher final pressure since it will cool off more by the time it is in the water. I often see them use 3200 PSI then instead of 3100 PSI.

[@bayardtaylor2990]

Can I fill one tank with another ? And what will. Need. .?. Thank you sir. , 🙏🙏

[@AlecPeirceScuba_SeaHunter]

Need a yoke to yoke connector, check Google. Note that depending on the starting pressure in both tanks, you may not have enough in each tank after equalization to safely dive.

[@Engineer9736]

I have such hose... was like 160 euros (i think in dollars about the same). But indeed... If one bottle is 50 bars and the other 150, you end up with 2 bottles at 100 bar. Or similar math for psi. 160$ is quite a lot of money for the low chance that you have a true "business case" for such action. Though i do use it before filling my tanks, so the tank with the lowest pressure doesn't heat up as much during filling, so more air will fit in it.

[@kaboom2800]

Can i refill my scuba tank with the normal air compressor used in Car Mechanic Work shop?

[@AlecPeirceScuba_SeaHunter]

You can refill it from any source BUT if it's not certified breathing air, never dive it. Auto compressors only care about pressure, NOT purity of breathing air which divers require. To see the high standards breathing air must meet, read this. www.airchecklab.com/resources/standards-specifications/scuba-sport-diving-compressed-air-specifications/

[@kaboom2800]

@@AlecPeirceScuba_SeaHunter thanks for the information.

[@uncatila]

@@AlecPeirceScuba_SeaHunter I owned the Mr c dive boat and according to fireman captain Stan Even the high pressure hoses on the compressor need to be certified for breathing.

[@farooque2911]

Respect for the simple explanation 🫡

[@AlecPeirceScuba_SeaHunter]

Appreciate the feedback my friend. A

[@nayaleezy]

fascinating... but why not just replace all your LP bank with HP bank again?

[@AlecPeirceScuba_SeaHunter]

Economics and physics. LP's are easier and faster to fill while HP's are the hardest to fill. Visit your LDS and ask to see their filling setup. You should find the setup is in proportion to the number of tanks they fill daily. A.

[@SolarSeeker45]

That's well and good but wouldn't you get a larger number of total fills by starting out all the tanks with 4500 psi at the beginning of the day? It would also save time since the first few customer's tanks would only need to be filled once. I'm not really convinced that it's saving on the total running hours of the compressor either since it's ultimately pumping the same amount of air at the same rate regardless of weather you turn it on once or 10 times. I do agree that it's more friendly with the neighbors. Why not have a smaller booster compressor trickle filling the system in between times?

[@AlecPeirceScuba_SeaHunter]

There'd be no harm & perhaps some benefit from filling all of the tanks to 4500. Cascading the fills will still give many more fills. Back to that in a moment. The downside to filling all the tanks to 4500 is firstly the cost. 4500psi tanks are markedly more expensive. Plus you need more of them so the initial cost is high. Also, filling to 4500 psi is much harder on the compressor. And after all that, there's no real need to do so. Now to the cascade system. The #1 bank, low pressure, high volume (we had 20 tanks here), is filled to 2500psi. #2 bank, low pressure, medium volume (we had 10 tanks), is filled to 2500psi. #3 bank, high pressure, medium volume (10 tanks), is filled to 4500psi. A customers tank @ 500psi is filled from #1 to whatever pressure is in that bank - let's say 1800psi. Then it's filled to #2 to it's remaining pressure - let's say 2300psi. Then #3 tops it up to 3000psi. While not a truly accurate measurement, lets say that you have taken only 700psi from bank #3 rather than 2500psi from the single bank. Since not much volume is removed from #3, you can top up many tanks before it's pressure drops to 3000psi. However, if all of the bank bottles are at 4500psi and you simply fill the customers tank from the entire system, as soon as the system drops to 3000psi, you're done. Time to start the compressor, even though you still have a heck of a lot of air in those tanks! Pumping all of that air not only cost a great deal, and wore the compressor, now you can't utilize all of the air in them! It can be calculated fairly easily using the volumes of the customers tank AND knowing the volumes of the cascade bottles. But we don't fill nor sell air by volume. Divers could care less how much volume is in their tank They want pressure. You must give them 3000psi. It may sound and appear to be illogical but, trust me, you can fill many more tanks by cascading than by simply filling from a large bank. Alec

[@AlecPeirceScuba_SeaHunter]

BTW, Boosters are great but, (there's always a but. It's called Life!), Boosters are VERY expensive, fairly high maintenance, noisy & they still require a fairly high pressure to operate. And of course, if you understand Boosters, they waste air, not a lot, but some.

[@SolarSeeker45]

@@AlecPeirceScuba_SeaHunter I wasn't saying to have a single large bank. I was just saying to fill the "bulk" side of the cascade system to a higher pressure so that you have more total air. The first few customer tanks could be filled all the way using only the bulk tanks and then use the cascade system like you do normally as the pressure in the bulk tanks begins to drop off.

[@Yggdrasil42]

@@SolarSeeker45Highet pressure tanks are more expensive to buy and it puts more wear on the compressor and filters to fill them all the way. The higher the pressure of the container it needs to pump into the harder it needs to work. My compressor manual gives me significantly lower filter lifetimes when I fill to 300 bar instead of 230 bar. More than just the additional volume would account for.

[@toriless]

My shop uses 3000 instead of 2400 and then tops off with the 4250 so they do not need to use as many tanks for their cascade system.

[@AlecPeirceScuba_SeaHunter]

That sounds perfectly fine for their store and customers. There is lots of possible variations based on # of fills, time required, cost, space, compressor size etc. Thanks for sharing.

[@amadeuss3341]

I don't think this system saves compressor time. If you fill 10 tanks, that's 800cu/ft from the bank , that you have to fill back with compressor. But it defenetly makes things faster, it's only takes 1-2 min fo fill. so you don't have to chill there while compressor pumps up your tank up. Similar to reverse osmosis water filter. Might be wrong though. 🤔

[@Kebekwoodcraft7375]

I was thinking the same thing, save on time to fill and how many you can fill in shorter time, the perpetual motion don't exist yet .

[@wowfreaker]

At my dive store you walk in. Hook it up and let r fill. It stays there for a bit because as the bottle cools extra air gets added. So you walk away with a bottle that doesnt lose pressure due to heat and a very very full bottle.

[@KimonFrousios]

True. The compressor has to compress that amount of air, regardless of which bottle it goes into. If anything, it has to work harder to get up to the higher bank pressure than it would for direct-to-bottle pressure (if it's anything like pumping bicycle tyres). Aside from time, you also get a little more air, since you are not filling your tank with freshly hot air. The airbanks could have had some time to cool off, and then the air further cool a little bit as it expands into your tank (bigger effect when filling lots of tanks in parallel).

[@cerebralm]

You're assuming that the compressor makes perfect use of it's running time. But in reality the compressor would have to speed up/slow down every time you want to use it, and that adds overhead every time it runs. Better to run it in one long session then lots of starting and stopping.

[@AlecPeirceScuba_SeaHunter]

Lots of discussion to your point. At large shops like Scuba 2000 (pre-COVID), we would fill 10 pool tanks (8 students + 2 instructors), filled 3 times a day for Sat. and Sun. o/w classes + weekend fills + o/w cert diver fills. Our cascade system was setup for peak use on weekends then turn on the compressor at night (cheaper electricity, cooler inlet air temp, etc.). If your setup for the average number of fills per day, customers will be waiting or leaving so each shop is unique. Thanks for the question and keep discussion everyone.

[@tombackhouse9121]

I don't know if you're still reading the comments on this video, given that it was published a year ago, but here's another way of thinking about it: When you run your compressor, you're storing energy in your bank, and when you fill a SCUBA tank from the storage bank, you're transferring some of that energy into the SCUBA tank. But the transfer isn't perfect. If I take a tiny bit of air at 3000psi from the bank and put it into an empty SCUBA tank, so that the tank has, say, 5psi afterwards, almost all of the energy is lost. It has to be, because the little bit of air I moved went from being 3000psi (lots of energy) to 5psi (barely any energy). The rest turns into noise and heat. But if the tank were nearly full, so that instead of going from 0 to 5 psi, the tank goes from 2995 to 3000 psi, then damn near all of the energy in that little bit of air is preserved. So the inefficiency of transferring air from a storage tank into a SCUBA cylinder is directly related to the pressure difference between them. So it follows that, for greater effciency, you would use a series of banks of increasing pressure, so that you never have a huge difference between the tank the air is coming out of and the tank the air is going into :) I realise that this is, really, just a rephrasing of what you said in the video from a slightly different perspective. But, given that you are so good at making complicated ideas simple, and given that different people understand the same idea in different ways, I thought I'd throw my perspective (as a physics grad) at you, just in case it helps you find the right way to explain it to the next guy!

[@AlecPeirceScuba_SeaHunter]

I read ALL comments Tom and reply to all that I can without spending all day answering them. Some comments have sincere questions or experiences to share others rant on about nothing. Your point is a good one but in the time I have its a simple explanation for divers new and old to understand the basics and why your LDS air fill charges vary. Thanks and welcome to comment anytime Tom.

[@tombackhouse9121]

@@AlecPeirceScuba_SeaHunter I should have expected nothing less! Great video Alec, I always enjoy the insight into how things work on the dry side of the diving industry :)

[@maxtorque2277]

Here's a "fun" question to ask dive students - "Where does the energy stored in your tank under pressure go?" As you said, your compressor is, lets say, 10 horse power, it runs for a while and pumps a tank up to 3,000 psi. That tank clearly has a LOT of energy in it, stored in the gas under pressure (we all know that if that energy accidentally all gets out at once, you get a VERY big bang!). So you screw on your regs, throw the tank on your bank, leap over the side of your boat, and have a nice 1 hour dive admiring the fishes. At the end of your dive, your tank is nearly empty, so clearly the energy now in that tank is also practically nothing, so where has the energy gone? ;-) #thermodynamicsisfun

[@AlecPeirceScuba_SeaHunter]

Very interesting question Max. What's the answer? For other viewers of course!

[@maxtorque2277]

@@AlecPeirceScuba_SeaHunter The answer, perhaps somewhat obviously, is the energy ends up in the ocean as low level heat ie It warms the ocean up! When your compressor compresses the air, it creates potential energy stored in the gas under pressure. It also produces some "waste" heat, because the compression process is not 100% efficient. That heat is lost to your comnpressor room, as the hot gas cools down in your resevoir bank, or cools in the customers cylinder sat on the floor of your shop. When you dive with that tank, each time you breath in, a little bit of the potential energy is lost from the tank ie the pressure falls, and the gas accelerates through the 1st and 2ns stage, and then fills your lungs. Close to the surface, when you are breathing air pretty much at atmospheric pressure, the energy goes to pushing water out of the way as your lungs expand, and some is lost to heat and sound as it rushes at high speed through the system. That "hhhsssst" you hear each time you breath is sound energy after all! At depth, the air in your lungs is still under a greater than atmospheric pressure (the pressure it started at in your shop), so after you exhale, it continues to slowly expand against water pressure as it rises in your stream of bubbles, again, doing "work" on the water it has to push out of the way as it does so. What is slightly counter-intuitive is that as a gas is expanded, if it cannot "grab" some energy from it's surroundings (adiabatic expansion vs isothermal expansion - google it! lol) it actually cools down. This heat grab is what can cause regulators to freeze of course in cold water environments, because if you take heat from an object its temperature must fall. So ultimately, all the energy you so carefully pumped into the customers tank in your shop is lost to the ocean. :-)

[@toriless]

@@maxtorque2277 ...and when it is filled it heats the tank. The always get hot when being filled which is often why they will fill to almost 3200 PSI knowing it will drop to 3000 once cool.

[@alaind831]

@@maxtorque2277 "energy ends up in the ocean as low level heat ie It warms the ocean up" actually the the opposite, no ? the regulator (which can freeze due to pressure loss) cools the surrounding ocean. The tanks get really hot when filling, but cold when used as well...

[@MrShadowpanther3]

@@maxtorque2277 A very interesting question and an even more fascinating answer as I had never thought through the energy dynamic transfer of the entire process. This is another one of those "all this complexity happens without you even knowing" things!

[@garygerard4290]

I use to get my oxy tank for welding filled from a guy that had some dozen big oxy bottles all plumbed together. He'd open one then shut it off then open the second then shut it off and so on, down the line. Then before he'd disconnect the last bottle from mine he'd put that high pressure in the line back into one of his lower pressure bottles - And if I didn't need a receipt he'd knock a few dollars off the price - Ha Ha

[@AlecPeirceScuba_SeaHunter]

Well that's one cascade setup! At least your tank was filled.

[@chrisphilhower6029]

This like filling a Spare Air. Bought a Air Venturi pump like shown on their website. Use a couple of Filters in the line. Including a big one with Charcoal. I can't fill the 6cf Spare Air in one shot. I fill in stages. Allowing the pump to cool in between. Cascade Filling allows the Tank to cool a bit between the LP and HP fills. Might get a better fill.

[@AlecPeirceScuba_SeaHunter]

The compressor sounds like its not fast or strong enough for your tank. A

[@chrisphilhower6029]

@@AlecPeirceScuba_SeaHunter Spare Air has other models by the same company on their website. It will go to 4500 PSI. I haven't filled my 6cf unit in awhile. I forget how long it took from 0.

[@patriksamju]

Im still confuse. That's math. 😕🤔

[@AlecPeirceScuba_SeaHunter]

Very important math sir to get your tank filled quick.

[@toriless]

It averaging. The pressure will be in direct ration to the volumes. If the empty tank is 1/10th the volume it will take up 1/10th the air so the other tanks now have 90% as much air in them. The actual amount is much less with all those huge tanks which is why many shops use less of the huge tanks then Simco does but use higher pressure so they need very little at 4250 PSI. You can partially fill a lot of tanks with those big cylinders. You also do not need to run the compressor as long so it does not get as hot. When you our water out of a 2 liter bottle into your cup there is less water left in the 2 liter bottle, right. With air, less air means less pressure. You have reduced the mass and thus the pressure at the current temperature.

[@michaeldallas]

I think the fundamental piece of information that is missing is why you don't fill everything including the "great big tanks" to 4000 PSI. I am assuming that these tanks can't hold that amount of pressure. Getting tanks which are that big and rated for 4000 PSI would be expensive so you use these cheaper (lower pressure) tanks instead for the initial fill. Then you go to your smaller and more expensive (higher pressure) tanks to top up the fill.

[@AlecPeirceScuba_SeaHunter]

It comes down to physics, cost and time for a store. HP tanks go to 6500 psi but fill very slowly compared to LP's at 4000. The compressor output is the so LP's fill up faster than HP's. Next time in your LDS, ask to see their fill system and you can ask intelligent questions from what was picked up here.

[@MrMurray88mph]

Always PSI..

[@AlecPeirceScuba_SeaHunter]

When not bars, right! Ha

[@Engineer9736]

I think as a diver it's good to be familiar with both units (psi and bar), so if you ever dive abroad you can still understand what your possibly rented meters are saying. Might be easier to bring your own bar-unit regulator setup but then you may have to translate the bars to psi for your buddy. Big mess 😅

[@MrMurray88mph]

@@Engineer9736 well all around the world bars and meters is the norm 😅 But yeah, all around freedomland people use psi and feet. It’s just a very complicated way of diving (and this comment comes from a ohio friend of mine)

[@Engineer9736]

@@MrMurray88mph Yeah i live in Belgium, everything is bars and meters here too. But so far i already memorized that 200 bars = 3000 psi. The feet thing is too complicated to me to do an actual dive on. Yeah it's feet/3=meters but when you're 30 meters deep any extra math to do is just unworkable i think. May be better to just bring some bar gauges over.

[@MrMurray88mph]

@@Engineer9736 Well the best is always to dive with what you are familiar with. And when you're diving around the world, best to have your mask, regulators, dive computer and fins. those are in the order you should buy your dive gear.

[@casperairsoft]

Its weird that poeple dont understand this basic math. Preassure cannot be gained ore lost (Between tanks). The volume just shifts. And with greater lets just say bottle space becouse more space for the air wich means that with the same amount of air there is more room so less preassure.

[@AlecPeirceScuba_SeaHunter]

I taught high school science long ago and students got it back then when i drew it out. Pressure just 'moves' but most divers just want a quick fill without knowing the very exact science and physics behind these systems. Glad you liked it. A

[@wanaraz]

How could helium get into a tank? Two children died from helium in a tank. It don't make sense.

[@AlecPeirceScuba_SeaHunter]

Suspect it was a dedicated ballon filling tank. In scuba air helium is a minor trace gas or no significance. A

[@jerryocrow1]

Thannk you. Next time, pretend you are punished by the word (e.g. You get $400 to do the video but you are charged $1/word for every word over 1500 (typical short essay). This script will have you working for free (instead of the millions you get from KZbin). Or, rewrite the script so you make $400. Thank you for sharing your knowledge.

[@AlecPeirceScuba_SeaHunter]

None of what I do is scripted, much to Kevin's displeasure. Good points. A