Need help with the "details"

[gxsr_sarge]

So after pouring over the Oxyhackers book and tons of print-outs and articles from this and other forums (you guys are a wealth of knowledge), I finally decided to go with the following (and rationale therefor):

- partial pressure blending system (while I like the nitrox stick notion, I want the flexibility of blending He in the future for trimix - sounds very tricky already, let alone with the stick). I don't mind the extra O2 process and cleaning procedures.
- Bauer Oceanus (have ONLY heard/read great things about Bauer. Junior model not rated for continuous operation/filling banks).
- 3 bottle bank/cascade system (2 LP and 1 HP).
- LF hyperfilter for OCA (I know it's debatable but don't want to mess around)
- maybe a Haskel booster (when I start mixing Trimix to save He) - otherwise not worth the $$ now to leave only 500-ish PSI of O2.

I plan to mix about 10-20 tanks worth of Nitrox and about the same for air each month.

Now, I'm kind of stuck trying to figure out the detail and lost in a forest of information. The book is great but unless I read it too fast, it doesn't really layout details in terms of "you need to put this here....". In other words, what regulators, valves, throttle valves, check valves, whips, hoses, fittings, gauges, tubes, analyzers, etc. I have a rough layout of the system (see pic - yes, ripped off from "nitroxmadeeasy.com") but now need to get down and dirty in the details and start buying hardware! I downloaded the GMC catalog and that is an entire other forest of forests.

Does anyone out there have a detailed schematic or list that they would like to share?

Maybe some general advice could help like:

-Does each bank have to have it's own gauge and/or valve?
-Where do I have to put in check valves (to prevent back flow?)
-Where do I have to put regulators (O2 and where else?)

Maybe I'm "over-engineering" this in my mind?

Thanks

 

[pescador775]

Check out Decostop for that stuff. Anything simple on its face can be made complicated and those guys are master plumbers. There is a sticky on the same subject. Also, there is a "DOC" on this board who started from scratch and provided his results during the setup process. See "search" for the thread. Pretty impressive continuous blending operation after starting from zero. As to PP blending, ho humm. After developing some confidence, building two sticks, doing the math, and working with twin 02 analyzers you will wonder why you ever messed with PP. Helium mix can be pumped through the compressor with one or two sticks. I think I invented the one stick deal; at least, I was the first to write on SB about it. Omar gave me a ration of crap. Shortly thereafter, one could buy the single mixer over the net, hmmmm. I still think it is easier with two unless your compressor has constant output at all pressures or an He analyzer is used. Again, learn the math. For me, it is algebra. Others do a sort of sums game adding up amounts of gas partial pressures in their head. Don't forget, if you do the mickey mouse PP mixing there are compressibility factors to apply. Bring your booster. What to do when changing mixes? Take your choice from this thread:

http://www.scubaboard.com/forums/co...tems/236471-how-do-i-get-28-1000psi-32-a.html

Single stick:
http://www.scubaboard.com/forums/te...lties/84454-building-trimix-nitrox-stick.html

 

[gxsr_sarge]

Pescador, I appreciate your response.

I checked out that forum and couldn't find that thread. There are a few "docs". Any more clues?

Also, and I'm not being a wise-ass - just curious , if blending is so great, why don't more dive shops use that method for blending Nitrox? It seems that all they would have to do is bank a few H's or T's full of 32% or 36% and just sell it away?

I'm not opposed to blending in the future. Once I know what I'm doing the "old school" method (or get tired of pp), then I'll probably build a stick.

Cheers

 

[pescador775]

Also, there is a "DOC" on this board who started from scratch...

I mean what I say except when I don't. Scubaboard has the worst search engine; I had to modify the search several times in spite of having known, correct terms. Eventually, I used "NEMA" and that worked. After getting his handle I looked up all threads started by him.

I haven't been in a dive shop in years but my understanding is that many of them stock premix.

http://www.scubaboard.com/forums/co...tems/218138-plumbing-assistance-please-2.html

http://www.scubaboard.com/forums/co...ems/218727-alkin-w31-compressor-question.html

http://www.scubaboard.com/forums/co...ems/235001-can-you-believe-im-up-running.html

 

[dannobee]

Personally, I'd pass on the PP blending and step right up to the nitrox/trimix stick.

The shops around here bank 32% by using nitrox sticks. I suppose the ones doing partial pressure blending are scared or simply don't sell enough nitrox to justify banking 32%.

Standard GUE mixes all top off with 32% (21/35, 18/45, 15/55).

You can use the single stick and O2 sensor method for mixing trimix, too. Start up the compressor, turn on the oxygen until the sensor reads 32%, then crank up the He until the sensor reads the appropriate amount (i.e., 21, 18 or 15 for the mixes above). Check the content of a tank or two with an He/O2 analyzer until you feel comfortable that you're doing it right.

I can mix the standard mixes using the stick and get results within 0.3% or less.

Except for 50/50, I don't PP blend anymore.


.

 

[gxsr_sarge]

Personally, I'd pass on the PP blending and step right up to the nitrox/trimix stick.


Except for 50/50, I don't PP blend anymore.

.

dannobee - I agree that it seems easier to use the stick.

I'm taking a DSAT blending course in a few weeks. After which I'll be able to get a better feel for what's involved and decide which method with finality.

I went over the Oxyhacker book again (especially the "Hardware" chapter) and it turns out that it has a lot more information on the details/hardware requirements than I first realized. I guess it's because when I did my first read through, I was much less informed.

Cheers

 

[Scuba Duck]

Contrary to Dannobee's post, when you use a single oxygen analyzer to try to make Trimix, you need to start by adding the Helium first. Say you want a mixture with 50% He in it, add the Helium to drive the O2 Analyzer down to 10.5%, then add O2 to supplement to the desired oxygen concentration.

When you add either oxygen or helium to your Nitrox Stik, you are displacing the air (both Nitrogen and oxygen) being drawn into your compressor. So if you add the oxygen first and then the helium, you will displace some of the air, a componet of which is oxygen, and you will not get the desired outcome, as you are not measuring the helium or nitrogen concentrations directly.

Adding the oxygen won't change the amount of helium going into your compressor. However adding helium, will change the amount of air you draw in and subsequently your oxygen and nitrogen levels.

So... if you want to blend trimix without a helium analyzer, add the helium first to establish the helium flowrate (you'll have to do some math to figure out what the oxygen analyzer should read), then add the oxygen.

 

[dannobee]

One more thing regarding O2 sensors, if you set your mixer up with two O2 sensors (blending trimix), they won't match. I suppose brand matters as I only use the teledyne ones, but they seldom match when watching them.

I took two new sensors, swapped them around between the two analyzers, added the O2 at the He port, then at the O2 port, swapped with old sensors, and concluded that the sensors aren't anywhere near as accurate as we hope.

 

[dannobee]

Contrary to Dannobee's post, when you use a single oxygen analyzer to try to make Trimix, you need to start by adding the Helium first. Say you want a mixture with 50% He in it, drive the O2 Analyzer down to 10.5%, then add O2 to supplement to the desired oxygen concentration...

Either way works as long as you test the first tank and make adjustments to your setup, then use the same method each time. If you add O2 first, drop the O2 reading a bit otherwise it'll be too high. Helium has some compressibility issues, so he'll have to analyze the first tank or two regardless of the method.


The numbers for standard GUE mixes will be 13.4%, 11.4% and 9.4% for 21/35, 18/45, and 15/55 respectively if you're adding the He first.

The big caveat is that compressors do not have the same output throughout the pressure range, so some fiddling with the regulators is necessary when filling.