Home Brew ?

[TobinGeorge]

James,

I have two 15/30's but I already have 30 hp of low pressure air compressors.

At the speeds I'm willing to boost O2 drive gas is never a problem.

Regarding shop or LP compressors; Most of the Lowes / Harbor Freight type are optimistically rated, the HP is not "real" and the CFM delivery. Many of these lead short brutal lives.

Duty cycle is another consideration. If the compressor runs and shuts off and gets time to cool, you stand a chance. If the compressor is running all the time to keep up, short brutal life follows.

Adding receiver capacity is an effective means of reducing the duty cycle, dead compressors sitting on perfectly good tanks are surprisingly easy to find (oddly enough) This does require more space for the installation.

I'd seriously consider an electric drive gas booster. Just one apparatus to buy, install, and keep happy.

Tobin

[fdog]

Thanks, Tobin!

How effective is it to run off banked air? How about smaller shop air - do you just slow down to 1 cfm of boosted gas or something slow like that?

<begins search for "electric drive gas booster">


All the best, James

[TobinGeorge]

Thanks, Tobin!

How effective is it to run off banked air? How about smaller shop air - do you just slow down to 1 cfm of boosted gas or something slow like that?

<begins search for "electric drive gas booster">


All the best, James

The extra receiver (LP bank) capacity allows the shop air comp to cycle off and stay off long enough to cool a bit vs running full time.

You can of course slow the booster via needle valve inline after the lp pressure regulator.

The lower the supply gas pressure vs the tank being filled the greater the drive gas required.

Scavenging the dregs from a He bottle takes alot of drive gas or a lot of patience.

Tobin

[ligersandtions]

When I talk about home brewing i assume that you make the investment in a compressor. Not putting mixes in tanks and sneaking them into unsuspecting dive shops and having the monkey put the air in the tank to make the final mix.

How does this work? I've heard of people putting oxygen into their own tanks and taking them to shops (read: Sport Chalet) to be topped off with air. Now, I get it if the shop is doing PPB to get 21%, but would there be an issue if you just went to SC and had them fill with air (not blended to 21%, but actual compressed air....not O2 cleaned)?

Seems that there would be an issue, but maybe I'm wrong....maybe people just haven't had any issues or maybe they got lucky???

[aainslie]

Hey James,

First off, there are three great boosters: AG30, AGD30 and the AGT15/30. The 15/30 is nice for going to lower pressures in your supply. AGD's are great if you have huge boosting needs. the AG has the advantage of being very simple and it's what I have.

Speed is a complicated issue. It's both a function of how fast you feed gas to it, and the difference in pressure between supply and the tank you're boosting. An AGT sucks up a lot of gas so you'll need at least about 8 cfm to really make it work.

I personally won't go much below 500 psi, at which point I move the tank to my stick since on the stick, I can go all the way to zero. This is a really efficient way to use your tanks - first use them with the booster, then at the end of their lives use them to feed a stick.

[College Diver]

Another is the set of incredible spreadsheets that I wrote ( ) to do trimix through a stick. i discovered that the math in, inter alia, oxyhacker is wrong, and wrote a spreadsheet to correct the error.

Andrew - any chance in a distribution of said spreadsheet(s)?

[TobinGeorge]

How does this work? I've heard of people putting oxygen into their own tanks and taking them to shops (read: Sport Chalet) to be topped off with air. Now, I get it if the shop is doing PPB to get 21%, but would there be an issue if you just went to SC and had them fill with air (not blended to 21%, but actual compressed air....not O2 cleaned)?

Seems that there would be an issue, but maybe I'm wrong....maybe people just haven't had any issues or maybe they got lucky???

Yes there is a potential issue.

When you PPB you are introducing pure O2 into the tank at high pressure, sometimes quite high if you are blending on top of a partially filled cylinder.

For example lets say I have a 1/2 full al 80 of 32% and I want to avoid dumping the 1500 psi of 32 in the tank.

I need to add 14% of the "missing" psi in O2, then top with air.

3000 - 1500 = 1500 1500 * .14 = 210 psi. I need to add about 210 psi of pure O2 on top of the 1500 psi of 32% already in the bottle.

1500 + 210 = 1710. I will be adding Pure O2 at over 1700 psi.

What happens when that pure, High pressure, O2 encounters some "fuel" that was left behind by the "Grade E" (not Modified Grade E or OCA) gas from your local dive shop?

Repeated air tops from "unclean" sources can eventually lead to bad things happening.

Not an issue is the air tops are OCA. (Well less of an issue, no real certainties when dealing with high content, high pressure O2)

BTW, my example shows how easy it is to get to the point where the O2 is at fairly high pressure, the risk goes up with pressure, but are still substantial even at much lower pressures, 250-500 psi is plenty to make things exciting.

Tobin

[aainslie]

Andrew - any chance in a distribution of said spreadsheet(s)?

Here's a post I did years ago on TDS:

I bank 32% using a homemade stick. Here's what I've learned:

- I generally have to overshoot by about 1%, i.e. I mix to 33% on the inlet to get about 32% outlet. Frankly I've never really understood why. I've tried compensating for humidity and temp but this rarely makes for more than about a 0.5% error or so in SoCal weather conditions. It may be leaks in my system. At any rate I suspect this "factor" difffers for different setups. The key thing is to find what it is for YOUR setup and then regularly compensate accordingly.

- There's about a 2% change from zero pressure to full pressure on the compressor because of changes in flow rate. You see this most when you drain the two drains. Generally if I'm filling at around 4000 psi, when I drain the mix will temporarily drop to about 31% and then go back to 33% when the pressure builds back up. I don't get as big a change as you seem to be seeing.

-Trimix is a whole other problem. What I do here is to set it up using two O2 monitors and an O2 subtraction calculation, then on the HP side I have a first stage to drop pressure for an He and yet another O2 monitor, where I adjust input until the output is calibrated. I then record these settings and use them as a starting point next time. Doing it this way I can generally be within 1% on O2 and 5% on He regularly. I then fine tune using a booster at the end to get it as close to exact as I feel I need for that dive.

So my plumbing roughly is:

Inlet - add helium - mix - add O2 - mix - compressor

The way the subtraction method works briefly is as follows. It's a little counterintuitive but the best way is to track N2 in the mix.

Let's say you want to mix a 10/70 mix. You need to do the following: your mix must be:

70% He
10% O2
20% N2

How much of this is air? Well, the best way to work that out is by tracking the nitrogen in the air, since that's our only source of N2. It is:

Air% = 20/.79 = 25.32%

So the mix has to be:

70% He
25.32% Air
3.68% Oxygen

OK, so if at the first monitor, we're mixing a mix that consists of 70 parts He and 25.3 parts air (note I'm NOT using percentages because we're going to add the 3.7% O2 later, so things don't add up to 100) then the % O2 in this mix is:

25.32*.21/(25.32+70)

But we can restate this because we know that what was missing on the bottom (aka denominator) is the extra Oxygen. So we can restate the denominator as

25.32*.21/(100-3.68)

I.e. we need a correction factor for the O2 yet to be added.

So putting all this together, the formula for the percentage of O2 on the first monitor is:

%O2 = 100*((% Nitrogen)/.79)*.21/(100-(100-%He-%Nitrogen/.79)

= ((%Nitrogen/.79)*21)/(%He+%Nitrogen/.79)

I know this looks complicated. But this allows for the addition of O2 at the next stage.

So - back for our mix above. What are the numbers? Well, the % Nitrogen is simply 100-O2-He:

% O2 = (((100-70-10)/.79)*.21)/(70+(100-70-10)/.79)
=5.6%

But screw all that. Just use an excel spreadsheet. I've attached one that I use for all sorts of stuff including CB trimix blending. Look at the "remixing" tab, cells E20 to E22. This spreadsheet also lets you remix so you don't have to empty out old gases. it also lets you remix using a mix of PP and CB, by mixing air, 32%, helium and oxygen to get the required result. All in all it lets you do a remix almost any way you want. It's the result of 2 years' tinkering. Since it's a WIP some of the other tabs contain some half-finished stuff, and PLEASE make sure you understand the basis of my calcs and do a double-check before trusting anything here. But hopefully you'll find it useful.

[College Diver]

Thanks Andrew, I definitely appreciate it

[keri.lewis]

Interesting thread.. first one I've posted on since I got back to the forum - here goes..

Thank goodness for the lack of regulation in the USA (bet you don't hear that often...)

In the UK (and rest of Europe) we're going through the stealth regulation of the scuba industry. The M26 valve debacle - which specifies that cylinders for Nitrox must have a different valve from those filled with air - means we are all starting to struggle in the home-brew field. I guess I'll need a new set of adaptors, reg-stems and whip-connectors soon. Add to this the action being taken to restrict the sale of He to private individuals and the home-brew situation will get a lot harder.

Generally I am interested in the economics of home-brew gasses. In Singapore (when I leved there a 8-9 years ago) there was a huge premium on having somone blend your gas for you (think US7c/litre) that made a fill of 21/35 a thing of beauty to rival diamonds.. ($100+ for the He alone) so I got into PPB in my back garden - and topped the tanks at a dive centre where I worked.

In the UK it makes sense for a regular team to brew together - but not for the individual. If you're doing 6 twinsets a weekend or 3+ a lot of stages - then it makes sense. Otherwise bottle rental, the cost of keeping the compressor in good shape etc. out wiegh the cost of a fill of 21/35 (about GBP45 from the store) I still think it's expensive - but I don't get enough mixed-gas diving done to merit switching back to homebrew..

[College Diver]

Distance from a retail source blender (200 miles + round trip) is the predominant reason why our team up in Bakersfield began doing home brew. The cost break down on the gasses really isn't that much cheaper (~$60-70 buy-in per diver). We have been granted the blessing of using the LDS compressor - I think he is becoming more interested in the process now that we have shown the ability...

Planning another batch this weekend for a Sunday excursion...

[TobinGeorge]

Add to this the action being taken to restrict the sale of He to private individuals and the home-brew situation will get a lot harder.

I suggest you either **Start** (wink wink) a research firm working on superconducting materials, a leak detection service, a welding shop, or a MRI lab.


Tobin

[Garibaldi]

Upon return from the Doria trip, I headed over to see Glen Butler at Life Support Technologies. (the guy who designed the NASA Nitrox System at the Neutral Buoyancy facility) and had him give me the crash course in gas mixing. Suffice to say I got a world class education on oxygen handling, cleaning, gas mixing, atmospheric entrainment, compressors, boosters, diaphragm pumps, water cooled compressors, system design, etc. But also a practical approach to it all. Glen also showed me how to mix in the field with a hose and a gauge.

Glen is absolutely outstanding! His contributions to the technical diving field have largely gone under the radar. Plus, he is just a great guy!

[Garibaldi]

In 1993 I walked into one of the only 5 dive centers in the country (2 were in NY where I was)

What were the five?

I am guessing here but:

1. Key West Diver
2. Enchanted Diver
3. The Gas Station (Lou Sarlo and Bart Malone)
4. Scuba Adventures Unlimited (Jim "Former" Baden)
5. Ocean Odyessy (Wings Stocks)

What was the other one in NY?