Mixing stick

[oxyhacker]

Normally you always want to have a pre-compression analyzer on the stick itself, since this gives you a fighting chance to kill the compressor or cut the flow (one good reason why the hose connecting the stick to the compressor shouldn't be too thoroughly attached, as yanking it off is usually the fastest way to intercede) should the O2 spike, before the compressor explodes. So if a downstream/output analyzer is wanted, normal practice is to add a second analyzer (thought I have seen some setups with both an upstream and downstream port, where the analyzer can be moved from one to the other, the unused port being plugged with a stopper).

Most downstream (output) setups use a regulator to drop the pressure, since if you use just a valve it is often hard to adjust for just the right flow, and the pressure and flow will change radically as the output pressure changes.

 

[waterpirate]

Thanx guys,
My specific inquiry is about the the sensor at the bottom of the stick, prior to detonation/ sorry I meant compression. For downstream I plan to use oms anyliser to verify gas content prior to use. How would I configure that anyliser for use at bottom of stick and still maintain a recomended 2-3 lpm flow rate that they spec for good results?
Eric

 

[pescador775]

Waterpirate, I'm having a senior moment and don't understand your question. However, I can tell you what I do. First, I determined that measuring the output at the compressor is not necessary. It is fun and instructive for awhile but I disconnected mine after getting the hang of things. Importantly, it told me that the compressor must be purged before opening the tank valve. Otherwise, the operator will be busy second guessing and fudging the readings. The compressor downstream setup was a cheap 5 lpm adjustable oxygen reg screwed into the base of the final filter. Just requires a T fitting. The gas flow is set at 2lpm and routed to a sensor and analyzer bolted to the wall. Gas check at the blending stik is composed of a sensor screwed into the side of the plastic stik. The output runs to another analyzer bolted to the shop wall. That's right, I just screwed it into a hole drilled and tapped in the base of the stik. I didn't want to spend too much time and expense on what is essentially a kitchen appliance. I spent an hour and 20 bucks on the stik and a couple hundred on the hardware, two Miniox meters and small regulator, plus another 30 bucks to buy 6 brand new Harris regs for the oxygen tank. I don't know what I'm going to do with all that stuff but I did make up a travel kit with extra stik for use on my boat.

A couple years ago, Omar told me he was using a check valve at the air intake of the stik. Claimed he had trouble with gas escaping the intake. I don't know, helium is buoyant and it doesnt' cost anything to do it so what the heck. The intake filter on my stik is a small engine filter. The bottom is a threaded pipe screwed into the plastic cap of the stik. For a check valve I applied some glue to the pipe projecting through the interior of the cap and slipped on a non-return valve from a double hose regulator. This is a plastic cartwheel which has a mushroom valve---from a Dacor reg, I think.

 

[pescador775]

Oh, I get it now, you are asking about flowing gas through the OMS analyzer. You can do that for the compressor downstream setup but not the stik measurement. There is no pressure to generate flow. The stik operates at atmospheric pressure. You are not the first person to presume somthing like that. Once, I got a private Email with some very nice equations. The guy was trying to help me with some calcs I had published on SB. Still available, by the way--if you pump trimix. Well, his calcs had an extra "1" in them. This mysterious "1" was one atmosphere. In other words, he was assuming the stik runs at gauge pressure. However, gauge pressure of the stik is "0". Nice equations, though.

 

[rjack321]

The best solution is to get an El cheapo analyzer kit from Patrick at Oxycheq. This analyzer uses an external sensor. You can use a PVC "T" at the bottom of your stick and have a port for the external sensor. Costs $100

There's no good way to take gas, which is running under a very very slight vacuum in the stick, and make it flow through an analyzer which has an internal sensor.

You can use a reg to take a 2-3L flow off the compressor output and run it through that OMS, just like a tank. Not exactly a mandatory element to a mixing system, but nice.

 

[waterpirate]

Many thanx to you all,
The mystery is over and I will call Patrick and order the oxycheq cheapo the monitoring at the bottom of the stick. I have secured o2 bottles and am assembling the parts for the stick. I hope to be up and blending soon. will post pics of the set up when completed.
Eric

 

[oxyhacker]

In case there is still any confusion, you don't have to take any gas off the stick to analyze - you analyze it on the run as it goes by.

The only reason you want a certain flow on ordinary analyzers is because you want enough gas running over the sensor to completely immerse it in the mix, but not at enough flow to raise the pressure above ambient. Other than those two modest goals, flow just doesn't matter. Since the stick is open on one end it has to run at ambient or damn near. And since it is filled with a steady stream of the same gas as you want to analyze you know there's enough to immerse the sensor. So nothing else really matters.

The downstream/output regulator is an entirely different matter since the gas you are sampling is at high pressure, and so it is a lot easier to bleed some off and analyze it at ambient in the same manner as one analyzes a tank, rather than try to find a sensor that can handle 3000psi+ and an interface that would allow it to read out in FO2.

 

[pensacola]

Can someone post a picture of the setup that you have for the sensor at the bottom of the stick (prior to compression/detonation)? Thanks

 

[pescador775]

Prior to detonation? Hmmmm. A compressor does not normally have a diesel cycle. Well, I could post a pic. However, my setup is so elementary a picture seems redundant. Is it that you don't know what a sensor is? In that case, you could look up oxycheq's website. I think they have some pics. Basically, it is a small plastic cylinder about two inches long and threaded 16 mm fine thead, male. My blender is a plastic tube, 2 inches ID, almost 3 feet long and stuffed with spun steel ribbon (Gottshalk steel sponge). The idea is to drill a hole in the side of the tube, near bottom, and tap the hole such that the small sensor will screw in. That's it.

Others use a T fitting at the outlet of the blender and insert the sensor into the T. I'll defer to them to supply pics at their convenience.

 

[Hoosier]

http://home.insightbb.com/~museindy/Mixing Stik.htm

It is a simple and humble "Hoosier" mixing stik.... Anyone wants to buy this, please let me know....