Flow Rate for Checking O2

[mempilot]

What is the proper flow rate for analyzing O2 in lpm? I've been using 2 lpm, but someone told me that may be too low.

 

[DepartureDiver]

What is the proper flow rate for analyzing O2 in lpm? I've been using 2 lpm, but someone told me that may be too low.

I disagree. It depends on how you calibrate the meter. If you are just letting it sit or waiving it in the air, then you want a slow flow rate. If I remember right, the faster the flow rate the greater the reading of the O2, i.e. it is reading richer than you actually have. Try different rates and see what happens. However, my recommendation is that you keep a bottle of EAN 21 that came directly from the compressor (so you know that is what it is) and calibrate off of that at whatever rate you want and then analyze at that rate. This also has the advantage of calibrating with no moisture/humidity since that is also what you are reading. When calibrating by letting the meter sit or from atmosphereic air, the humidity in the air is supposed to be taken into account. So with this procedure, that can be ignored. I personally use a slow flow rate.

 

[mempilot]

I disagree. It depends on how you calibrate the meter. If you are just letting it sit or waiving it in the air, then you want a slow flow rate. If I remember right, the faster the flow rate the greater the reading of the O2, i.e. it is reading richer than you actually have. Try different rates and see what happens. However, my recommendation is that you keep a bottle of EAN 21 that came directly from the compressor (so you know that is what it is) and calibrate off of that at whatever rate you want and then analyze at that rate. This also has the advantage of calibrating with no moisture/humidity since that is also what you are reading. When calibrating by letting the meter sit or from atmosphereic air, the humidity in the air is supposed to be taken into account. So with this procedure, that can be ignored. I personally use a slow flow rate.

I'm using the analyzer at the LDS. It has 3 parts: the analyzer computer, the flow meter, and the tank valve fitting. I first calibrate it by attaching the tank valve fitting to a compressed air tank. I open the tank valve about half way and adjust the flow meter to read 2 lpm. After the digital readout on the computer stabalizes, I set the calibration wheel so the readout is 20.9. Then I shut off the tank valve, leaving the flow meter set at 2 lpm. I let the system bleed, and then connect my tank. I open my tank valve about half way and wait for the readout to stabalize. That is the reading I put on my tank.

I don't use an analyzer that calibrates off atmospheric air. The question I have is about 2 lpm and whether that will give a different reading than 3 lpm or higher? The LDS doesn't like using higher flow rates as they say it can cause damage to their system. I'm wondering what this threshold is and whether or not it makes a difference on my PO2 reading.

 

[DepartureDiver]

I see nothing wrong with your procedure. The 2 lpm sounds just fine to me. But out of curiosity, why don't you do a little experiment and calibrate at different levels and then measure at those levels. My hunch is you will see no difference. I actually use a flow of less than 2 lpm.

 

[oxyhacker]

2-4 lpm are the traditional figures, so you are on the low end but OK.

However no need to take it on faith. this is something you can detirmine for yourself. Try different flow rates and observe how they effect your reading - you should find a stable reading over a fairly wide range. Once you do pick a flow rate that is on the lower end of the range (no need to waste gas) but not too low, so you have a safety margin. That is to say, if you reading starts getting erratic at <1 lpm, then use 2 or 3. shake the sampler around a bit and bump things to simulate normal handling and be sure the setting remains stable.
My bet is that 2 will turn out to be just fine, though it does depend on the sensor.

 

[mempilot]

Thanks guys. I'll try a few different settings and check the results. I just didn't want to go against the LDS since it is his equipment. I'm going to be ordering an analyzer for myself later this spring. Do either of you have any recommendations?

 

[DepartureDiver]

I'll get back to you. I don't want to just recommend what I am using just because I am using it. There could be better now.

 

[NEWreckDiver]

What is the proper flow rate for analyzing O2 in lpm? I've been using 2 lpm, but someone told me that may be too low.

I use 2lpm. As long as you use the same setting for setting the meter and analyzing you tank you will be fine.