Air fill cost/price

[Arduous]

My LDS is very good to me. He charges me $3.00 to fill my Steel 100's and he does my pony bottle for free. Of course I do buy equipment and toys from him. For the most part I get very good fills in the 100's as well.

Dive Safe .......................Arduous

 

[dc4bs]

Hi U.P.

The idea behind banking 40% saving on the 100% mixing tank is simple.

If you do the math (or let a spread sheet do it for you like we did), you see that by using the 40% as a top-off gas instead of 21% air, you need to put LOTS less 100% O2 in to start out with for mixes over 40% and you dont need to use ANY of the 100% tank for mixes under 40%.

Example: 3000 PSI tank (starting empty = 15 PSI @ 21% O2)

To get EANx50 using 100% & 40% you would need to add only 505 PSI of 100% O2 and the rest (2480 PSI) of 40% O2.

The same fill using 100% O2 and 21% air would use 1101 PSI of 100% O2 and 1884 PSI of air to top off.

If the tank started off with 1420 PSI of EANx30 and you wanted to make it 50% for the next dive you could add 737 PSI of 100% (fill to 2157 PSI) and then "top-off" with another 843 PSI of 40%.

getting to 50% using 21% as top-off gas would have required 940 PSI from the 100% O2 tank. As EANX 40% from the compressor is cheaper than the 100% O2 he gets deliverd by the tank, it works out nicely.

Also, using the spreadsheet, its easy to punch in your values and simply top off what's already in the tank rather than emptying the tank first and refilling from empty or you can figure out the minimum you need to bleed off for certain combinations to work without wasting unnessary gas.

Any mix desired at less than 40% could be made using whatever combo of 21%, 30% & 40% seemed best for the job.

Heck, we donated an old 486 HP desktop to the shop just to be the dedicated gass mix machine. It now sits in the back on the corner of the workbench so whoever is doing the fills can punch up whatever mix values they need at any time.

The spread sheet we made takes max tank PSI, current tank PSI, current EANx in the tank, your "fill gas" (usualy 100% O2) and your "top-off" gas (usualy 21%) and creates a list of fill & top-off PSI amounts for all values from 21% to 100%. The entries that cannot be achieved by the current gass combo selected from the tanks starting values show up as "NOT POSSIBLE".

The owner was only going to bank 30% untill we showed him all this and since the membrain compressor can do up to 40% he has now decided to bank 40% as well.

 

[Uncle Pug]

Originally posted by dc4bs
The idea behind banking 40% saving on the 100% mixing tank is simple.

by using the 40% as a top-off gas instead of 21% air, you need to put LOTS less 100% O2 in to start out with for mixes over 40% and you dont need to use ANY of the 100% tank for mixes under 40%.

Just didn't know what you meant by *the 100% mixing tank*....

You meant the O2 supply tank... got it...

I'm not so sure you did him a favor though....

Banking the most commonly used mix and being able to give customers a fill off the bank is faster, more convenient, safer and less expensive (for the shop owner) than having to blend down to each mix.

The small extra psi penalty for using 30% as a topping gas rather that 40% is not a big deal... Just use another O2 supply cylinder in the O2 cascade when doing the higher PO2 mixes.

How many 50% fills as opposed to plan old 30% fills are done in the shop anyway???

So now he is banking 21%, 30% and 40% !!!
Better he should have put the extra 40% bottles into the 30% cascade....

 

[Lost Yooper]

Originally posted by Ferrara
Yooper,
Be careful. I didn't have a LDS that offered what I wanted so I started setting myself up so I didn't need one. It turned into a dive shop. BTW my shop does have the equipment and gases you need.

You want me to travel 10hrs+ for a trimix fill . I'm not even sure where the closest shop trimix station is, anymore. There used to be one a couple hours away, but I don't know he's still filling. Garage stations are more normal up here.

Where 'bouts are you in Indiana? I think our station will turn into a shop too if we're not careful.

Mike

 

[Savitar]

No one mentioned a LDS that does both internet sales and walk in.

I'm in no way affiliated with them, but they're nice people and I would like to give them a plug.

Divers Supply:

http://www.divers-supply.com

I go to the store in Macon. There are several stores, in Fla, SC, and GA. 9 locations plus the internet.

That's the way I see to make it worthwhile, consolidate with other dive stores, make big volume purchases for each store plus a central warehouse.

I've bought several tanks there at reasonable prices, even cheaper than mail order (no shipping charge).

BTW: I have my own compressor, a little gas or electric portable, it's extremely convenient to be able to get air anywhere I go, but... I'll have to fill 400 tanks before I break even.

I hope this wasn't a taboo, advertizing for a shop, I just felt it relevant to the topic.

Cheers,
Warren

 

[Ferrara]

Yooper,
Lafayette In. We don't sell trimix because we're not certified to blend it but we blend our own. We are certified EANx blenders and sell anything up to 100%02 just can't sell He without the card. We do allow "qualified" blenders/divers to use the station. Also for the right people I don't have a problem topping off their mix. Finding a sensible policy given liability concerns isn't easy so we take it a case at a time.

 

[Lost Yooper]

Leave it up to the lawyers and sue crazy nutts to screw everything up.

Mike

 

[dc4bs]

Originally posted by Uncle Pug

So now he is banking 21%, 30% and 40% !!!
Better he should have put the extra 40% bottles into the 30% cascade....

Hi UP.

Well, I'm not sure of the volume on the bank cylinders (about 4-1/2 foot tall and 8-9 inches across. He's got 8 dedicated for 21%, 6 setup for 30%, 1 for 100% and is planning to get a few more tanks. For now, he's gonna put 40% in em, unless he changes his mind, and see how usefull they are.

He may very well switch them over to 36% or combine them into the 30% bank later if they don't get used enough at 40%.

For now it's still in the "well try it for a few months and see what works best" period. I don't know if the new tanks are in yet (or even orderd). This is all still a thought experiment untill actual hardware gets used.

 

[Uncle Pug]

Hi Ed,
We have a few shops around here that got into nitrox and banked 40 but I really don't think they thought it through...

Every tank has to be blended up or down (unless someone wants 40) and that adds a man power load not to mention the opportunity for Murphy to get into the act.

Not only that, but it requires customers to wait for tanks to be filled (most of these shops require overnight!) and that is unacceptable in my book.

If a shop decides to offer say EAN32 and EAN36 and bank just those two then they can fill customers tanks while they wait and if the bank is low then just top them off with the membrane fed compressor.

For those deco bottles that need to be filled say to 50 use PP blending with a EAN36 top.

What if a customer comes in and wants EAN33.5 for that *special dive*??? Send him down the road! Or educate him ($$$).

Really it would serve not only the dive shops interests but the customers as well to teach *standard mixes* instead of *optimal mixes* don't you think???

BTW I only bank EAN32 and that is what I dive... I'm not a shop but if I were that is still how simple I would keep it. If I end up banking anything else it will probably be 30/30 Tx

 

[ebbtide]

well Rick ,
here in Nova Scotia it only costs 5$ a tank , now here we dont have as meny LDS's so we have to bug the local fire ,departments . all the firemen /women are more than glad to lend a hand in filling your tanks . and the setup they have for a compressor with all the air filters and sutch , must cost a pretty pennie .