Partial pressure nitrox fills at home?

[JFalzetti]

I know this topic has been discussed before back in 2006, but I didn’t quite get the full picture from the information available.

In the previous post the OP was asking if it was possible to have a tank of O2 at home that you fill your tank to the required Partial Pressure, then take it to the dive shop to have them fill the tank the rest of the way with air. I have this same question.

Could I go get a tank of O2 and fill my tank to the required Partial pressure, then bring it to my LDS and have them top the tank off?

In the post it was never completely clear if you could partial fill a tank with O2 and bring it to the LDS and have them fill it the rest of the way. Then again would it even save you that much to do that? A standard fill is $10 ($7 with card) and nitrox is $17 (not sure if there’s a card).

For my situation I have a buddy who gives me free air fills, so it would make sense for me to do a partial fill of O2 and have him fill my tank. I just need to know if I’m able to go get a tank of O2 and partial pressure my tank and have him fill it on the shops standard air fill.

I’m also interested in potentially doing the complete fill at home. I understand this would cost a lot of money to start out. $3000???, but If you were to also blend your trimix that could obviously begin to make more sense.

Regarding nitrox if you spend $3000 to start out, and nitrox is $17 a tank, you’d need to fill 177 tanks to break even.

[I don’t know the math on trimix, but for fun let’s assume it’s an extra $1000 in gear to do the trimix and assume trimix is $120 a fill (no idea on this) not accounting whatever amount you’ve used on nitrox, so total gear is $4000, that’s only 34 tanks to be even.]

Thanks for messing around with this idea with me!

 

[rddvet]

You can, but many shops will tell you to screw off since you're basically costing them money. With the prices of Nitrox imo it's a waste. If you were planning on filling trimix similarly, then yes. But there's a reason I have a compressor, booster, and bank tanks. Dive shops suck (OW shops at least) and trying to pp blend without a booster or compressor can be a pain and lead to alot of wasted gas (ie you need 2000psi of oxygen but your supply tank is at 1900psi.)

 

[tbone1004]

waste of money to do it IMO. It's very wasteful. Better off to build a nitrox stick at your buddies house and get constant fills there.

 

[ChuckP]

You'll need 3 or 4 Oxygen tanks or a booster and plumbing - no way that would be worth it.

 

[JFalzetti]

waste of money to do it IMO. It's very wasteful. Better off to build a nitrox stick at your buddies house and get constant fills there.

My buddy works at the dive shop and that’s where I get the fills.

What is a nitrox stick?

If I “made a nitrox stick” could I bring it to the shop?

Also could I just get a compressor and make one at my own house?

 

[broncobowsher]

It gets wasteful of the O2. Without a booster you are limited to what is in the O2 bottles for pressure. If you are wanting a strong mix, even more limiting. Top off, even worse.

When your new O2 bottles are starting at 2200-2400 PSI you run out of transfer pressure. The way around this, how many rebreather divers do there home O2 fills, is a booster pump. Now you are no longer just equalizing pressures, but actually pumping place to place.

The other side of things, how the fill shop (your friend) treats things. I know shops that have a basic compressor setup and they just fill 2 or 3 tanks at once. Open the valves, equalize everything, and push more air on top. This could easily result in your O2 equalizing into another tank and air put on top of all of it. You would weak a weak mix and someone who though they were just getting an air fill suddenly gets a Nitrox mystery mix. The shop (your friend) would have to know what you are doing and fill correctly. Make sure the supply pressure is never less than your starting pressure, don't add another tank to the compressor during the fill where your gas may bleed back into the line as another tank equalizes, etc. So just stopping by a shop and asking for air on top may screw you and maybe someone else as well.

 

[johndiver999]

If you are only doing nitrox and your buddy gives you free air fills, it is quite possibly "worth it" to mix your own. The cost is a whip and gauge and rental cost on the oxygen bottles and probably an analyzer.

Should be less than maybe 1000 for everything. I'm not sure why someone would say it is wasteful, especially if you have two oxygen bottles and several scuba bottles - you should be leaving little oxygen in the fill bottles.

It is a pain dealing with those giant heavy bottles, especially if you have to pick up and return, but avoiding $17 nitrox fills is enticing if you dive a lot. You will need a truck or van.

Also, with a little rithmatic, you can conserve oxygen if you don't completely drain the tanks before adding oxygen, which most dive shops do for convenience and simplicity.

There are technical issues with oxygen clean compressor etc. that you need to be aware of.

The big factors would be what does a bottle of oxygen cost (for fills and rental or buy) and how far do you travel to get it.

 

[TrimixToo]

Nitrox is relatively cheap. I honestly wouldn't bother. The training, analyzer (though you should arguably own one anyway even if you don't mix) and cost of a decent O2 clean booster pump and a compressor to drive it will take forever to pay you back, and that's if you dive a lot. The O2 tank rental alone is about a hundred bucks a year. Also, you have two choices. Tell the filler or don't. If you tell the filler, you will need agreement. If you don't tell the filler, you'll have to take what you get for the mix after the fill. Plus, you'll need the filler to supply O2 clean air for every fill and the tank and valve will need to be cleaned for partial pressure blending even if the filler does banked Nitrox fills.

Trimix, for open circuit, however, is notably NOT cheap. Were I a decade younger I'd go RB. Not sure what the economics would be then if I were starting over. For OC, though, the cost of local trimix was high enough that the (used) compressor, (new) Haskel, gauges, whips, analyzer, training, and such have all been repaid a few times over now. Also, I might be the only trimix blender in the county at the moment. The one LDS that mixed trimix stopped doing it after it was sold to new owners and as far as I know never started again. It's a long drive to the next nearest place from my garage.

HTH.

 

[boulderjohn]

Reading between the lines of previous posts, you will see that a lot depends upon your total situation.I have done this countless times, but I have a booster and a unique situation where it makes total sense.

Not only does a local shop let me do it, that is, in fact, how that local shop gets their own nitrox--from me. In our area there is very little call for nitrox, so they only use it for their instructors doing multiple dives per day. I show up at the shop with an oxygen supply bottle in my van, and they bring me their empty nitrox tanks (so I don't have to bother using the booster for that.) They then top off their tanks. I don't charge them--it only costs me a few dollars per O2 fill to make 36%.

In return for me giving them the O2 for their nitrox, they give me my fills and top offs for free. I put as much O2 and helium into my tanks as I need, and then I get them filled at the shop. (I actually do the filling myself.) If you are talking trimix, a booster is a huge factor--I can pump my tanks up as far as they need to be without having to worry about the pressure differential.

Before a trip to our deep water site (420 miles), I also get some tanks filled with just air. At the site, I use the booster (electric) to mix up the needed helium, oxygen, and air for all our trimix and nitrox fills. We do this in the motel parking lot, with me plugging the booster into our motel electricity. I have only blown a breaker a couple times.

It is good to know that the air you are getting in topping off meets O2 standards, and the air pumped at my shop does.

EDIT: BTW, a nearby shop does offer nitrox fills to the public, and they charge $25 for a cylinder. That makes doing it myself a good idea.

 

[WarrenZ]

Remember if you are doing partial pressure fills you need to maintain your tanks as oxygen clean one fill off of a compressor with a failed or saturated filter stack could introduce oil into your tanks raising your risk of a fire. I partial pressure mix my nitrox and take to a shop for fills but I also know that shop is pumping clean air and oxygen cleaning my tanks and valves.

Does your friend get his air tested before changing filters? If you can't verify the purity of the air going into your tanks a nitrox stick would roccomend you to pump premix nitrox lowering your risk. Have you read the oxyhackers book or have experience with high pressure oxygen and nitrox/scuba tank filling not all dangers are obvious.