Building a TRIMIX/NITROX stick

[pescador775]

Intresting picture omar, our stick looks nothing like that. ill try to get picture of our stick too to compare.

Pesca do you have a picture of your stick? If its in the Oxygen Hacker's Companion guide I will have my copy in a few days.

Here are some pics from my diving locker, explain later.
Pesky

 

[pescador775]

Speaking of two stage regs, they consist of two unbalanced sections arranged in series. It works but I don't understand why they stick with that design. All they have to do is copy the Conshelf first stage. That is a balanced single stage regulator and just look how compact that it is! It is certainly simpler and cheaper to build with far fewer moving parts. I don't get it. Ya know, I believe that the springs in a stock Conshelf could be jiggered to achieve the lower range common to oxygen regulators. One would have to install a flow restrictor fitting but that is not insurmountable. A bit of machining and a standard port could be installed in the Conshelf LP outlet. However, gauges would also have to be installed. Might not be worth the trouble on second thought. The single stage oxygen regulator is not a problem for Nitrox blending where a couple or three dive tanks are being filled now and then. The pressure drop in the oxygen supply tank is too small to cause significant fluctuation in the reg's output. However, helium requires large flows and I agree that a two stage would be more convenient. Otherwise, keep notes as to the regulator output level originally calculated and adjust if necessary.

 

[pescador775]

About the pics: the large tower is a nitrox/trimix stik. The small tower is a travel stik for mixing nitrox on my boat, etc. (I build portable air compressors for a hobby). The travel stik also functions as a premixer and it is mounted for experimental purposes although not connected when the pic was snapped. The small tank is a travel tank. The compressor pic shows a small oxygen regulator attached to the input of the final filter. About the analyzers: one small box attached to the travel stik, a large box (with alarms) attached to the main mixer tower, a small box attached to the main tower which reads gas fed from the compressor mounted regulator mentioned above. Not shown, a helium tank which was in the back of my truck.

 

[pescador775]

Thank goodness for the net where gas regulators are cheap as dirt. Awhile back, I bought six new single stage Harris regulators for $30, in other words, practically a gift. I believe it is possible to hook two of these in series to form a two stage reg. However, the "first stage" of the rig would need a stronger spring than the second stage. Looking in the parts bin I found a Western single stage with a strong spring. Therefore, hooking the 100 psi Western to the 60 psi Harris should do the trick. One would need a 1/4" plug and a 1/4" nipple, worth about 5 bucks. Also, there is the matter of an adapter to go from CGA 540 to 580 (inert gas). I already have one of those. I don't know, might be fun.

 

[jbisjim]

Just got my O2 hackers guide, time to catch up....

 

[pescador775]

If you are not into "technical" you will be after reading the "Oxyhacker", wonderful book. I've never taken a nitrox course or anything so can't claim to be a "tech" diver. I'm sure that the guys who write those course study texts and teach the courses know a lot more about it than me. However, Vance Harlow has done a service to those of us who don't wish to bother with all the certs and restrictions imposed by the industry; that is for those who wish to learn a bit of the "unofficial" scoop and dispense with the pedantry. I complain about the typos and omissions in Harlow's book but that pales in comparison to getting all that info for a paltry $30 or whatever.

 

[aainslie]

Hey Pescador,

You had a post ages ago about using a two stage process - I'm now certain it's wrong and wanted to give you my algebra. if you get a chance, let me know if you think I'm on to something.

Let's say that you want to get to PHe and PO2, by adding fraction a of O2 and b of He. Then the final pressures will be:

PHe=b/(1+a+b)
PO2=(.21+a)/(1+a+b)

Then solving these wimultaneous equations you get:

b=(.79/(1-PO2)/(PO2/(PO2-1)+(1-PHe)/PHe)

And the actual O2 level you want to adjust to for step 1 of your procedure is to add He until the PO2 reading drops to .21/(1+b).

This is what Omar was talking about in his original discussion. This is a small factor but it matters - in your original example instead of dropping the O2 reading to 11.5 you should drop it to 10.8.

This is just FYI - the basic idea is absolutely excellent!! Regards, Andrew