"High Pressure Vs Low Pressure" How Much Air Am I Getting?

[@pearabellum]

A hp 100 faber actually holds 101.3cuft when filled to 3442 and when u fill it past that u don’t gain air at a linear rate u actually get diminishing returns as the pressure increase cause air doesn’t follow the ideal gas law and a aluminum 80 at 3000psi actually holds 77.4cuft .not a big difference I just want to point out that u have to look at the manufacturer specs to get actual volume cause what they call the tank is usually rounded up to a bigger value .sometimes they r rounded Down but that is usually not the norm

[@LakeHickoryScuba]

Hello @pearabellum, the Scuba Industry has always rounded up, we do the same with gas calculations and table calculations. Thanks for sharing.

[@akm03051]

Your terminology is very confusing. You are calling an overfill a "hot fill". A hot fill is typically when the tank is filled fast and it is hot when it is done filling and then cools down to a lower than rated pressure. An overfill is when you, well over fill a tank.

[@LakeHickoryScuba]

Andrew Morency You are correct, sometimes when a tank is filled fast, we call that a Hot Fill as well. In the context of the subject, articulation and interpretation can change the meaning of a word and or phrase.

[@bloodymarvelous4790]

I guess I can understand not wanting to fill cylinders over 3000psi if that's a limitation of their equipment, or it reduces their output of how many cylinders they can fill. But overfilling a 2250psi to 3000psi... if that's how you operate that you just fill every cylinder to 3000psi regardless of rated pressure, you should not be in the business of filling cylinders. I'm also curious why a 3442psi is considered "high pressure". I would have thought 4300psi would be high pressure, but maybe those cylinders aren't common in your area as they would require a DIN connector. I don't think it's necessary to have high pressure cylinders, those couple of extra minutes of gas are nice to have, but not life changing. If you want more gas, diving doubles is the way to go, not getting higher pressure cylinders. But if you're buying new cylinders, you might as well get ones that can handle higher pressures. At the very least your cylinder will last longer (provided you take care of it).

[@LakeHickoryScuba]

Hello @bloodymarvelous4790, most of your questions I would refer you to the Compressed Gas Association and Department of Transportation. These regulatory agencies have guidelines shops must follow for safety and insurance reasons.

[@dixee6498]

I get the impression that you could name the shops in northern Florida that won't fill your tanks past 3k psi but of course I'm sure most of us understand why you won't name them out loud here on KZbin. Maybe we could get that list if we asked you in person? Lol 😃

[@LakeHickoryScuba]

Hello dixee6, one of the major shops that refuse to fill above 3000 psi, is Ginnie Springs Outdoors, in High Springs Florida. There are several others as well. I encourage all divers to call around and ask prior to planning a trip. This way there is no confusion once they have reached their dive destination.

[@justsoicanfingcomment5814]

Would be nice if I did not have to stand over the fill attendants in SW Florida to get them to fill my tanks SLOWLY so they do not heat up and thus do not cool down and leave me with less air than when they finished and so they do not over fill my tanks to compensate for filling them too fast. Nice video, clarified some things for me.

[@LakeHickoryScuba]

You’re welcome, glad you liked it.

[@naa62]

Hi Bryan, High pressure steel 80 and a Low pressure steel 80 both have the volume of 80 cuf does one have more air in it or are they the same ? I guest I'm looking for a simply answer if there is one . should you get then same dive time out of each if the dive was the same thank you NAA

[@LakeHickoryScuba]

Hello naa62, here is the simplest way to explain it. Both have 80cf of air in them, but one has a higher pressure rating. The steel cylinder has more stencil strength, thus can hold a higher pressure. Since the cylinder is smaller in physical size but can hold a higher pressure, you can put more physical air in it (physical air meaning cubic feet). We will have a video coming out in late March talking about the differences in both Aluminum 80cf cylinders and Steel 80cf cylinders. Stay tuned.

[@bloodymarvelous4790]

There is something to be said for how Americans size cylinders in capacity, but it also creates some confusion. An 80cf cylinder will hold 80cf of gas. So a higher rated pressure means a smaller cylinder. In Europe, cylinders are sized to physical volume. A low pressure 12 liter is the same physical size as a high pressure 12 liter, but the high pressure 12 liter can hold more gas. And since you can just multiply the cylinder size by the rated pressure to get the capacity, it's fairly easy to calculate how much gas you'll be able to carry. A 230bar (3335psi) 12 liter cylinder holds 2760 liters (97cf), a 300bar (4350psi) 12 liter cylinder holds 3600 liters (127cf). 300bar cylinders are about 10-12% more expensive than 230bar cylinders for 30% more capacity, but do take significantly longer to fill to capacity.

[@davidshumate4863]

You are a math nerd.I like the way you simplify this stuff.I have only been diving for a year

[@LakeHickoryScuba]

This is true, I absolutely love math. Glad you like our videos david shumate, and that you find them helpful.

[@billhazel4476]

Thank you for the information, this particular video is especially welcome. I'm a relatively newer diver (2.5 years approx 250 dives) diving in warm waters of Guam , The Philippines and the like. I get the part about the 80's I have mostly aluminum but a couple of steel tanks as well. My question is I have a LP steel 80 stamped 2400. One dive shop regularly will only give me 24-2600 as I have no + stamped on the tank. The other regularly gives me 3000-3500. Am I damaging this tank ?

[@LakeHickoryScuba]

Hello Bill, that is a great question. Even if the cylinder is stamped + rated, technically speaking yes you are damaging the cylinder. The elasticity of the cylinder is not as much as one might think, especially in the cylinder threads. However, the biggest concern is repeated fills day in and day out. When we think of a Hydro Pressure being 5/3's the working pressure (3000 psi cylinder boosted to 5000 psi), it is a given that filling above the working pressure once every 5 years is ok. I would even go as far as to say several times a year, there probably won't be much risk (and only if filled slowly). But then again, at what point does the cylinder reach its maximum elasticity. My suggestion is to go by manufactures recommendations. If its + rated, fill up to the 10% over mark, and no more. I routinely will fill low pressure steel cylinders for my customers (with a plus rating) to 3000 psi, but only cylinders that I have personally did a visual on, and feel comfortable with their condition. The cylinder is most likely to rupture during the filling process and not so much so afterwards. This being said, the fill operator is the one at the most risk. All this being said, if you are diving just a few times each month, I wouldn't worry to much about boosting your cylinders, however, if you are diving several times a week, then I would maybe only boost a cylinder once a month. The more you stretch a cylinder, the quicker its elasticity breaks down. Hopefully this answered your questions.

[@billhazel4476]

Thank you for your answer. I was filling that tank up twice a week but I will no longer let it be filled beyond 2400-2600. I will use one of my 3000 cf aluminum ones instead. That tank I will only use on dives that I feel 2400-2600 will be sufficient. Again thank you for your KZbin and Scuba Pro contributions as they have taught me a great deal!

[@LakeHickoryScuba]

You're welcome, glad you have found our videos helpful.

[@rjmidd2650]

So is there any issues using a LP tank with any of the current regulators set ups? I am fixing to buy two 85cf Faders instead of a AL 80. Thanks

[@LakeHickoryScuba]

No issues at all Ray Middleton.