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*

I would retain the bubble device. 

You have to remember that the flow rate is not critical, all you are doing is making sure that 
you are putting sufficient P10 into the flow counters to compensate for leakage/diffusion 
through the very thin (and somewhat porous) polymer window. 

The only role of the outflow is to give you assurance that you are putting in at least slightly 
more than is diffusing out, so the bubble meters are ideal for the purpose.

You want the bare minimum flow to achieve this, as P10 is really expensive.

I doubt whether you will find a rotameter capable of registering this bare minimum flow.

The bubble "meters" also have the advantage of preventing back diffusion of air into the flow 
counters should the flow stop eg if the cylinder runs out, or if someone inadvertantly turns the 
flow off.

Incidentally, for a stable flow the regulator output pressure should be appreciable (say 10 to 
20psi), and the flow adjustment done with a needle valve (a restrictor) downstream of the 
pressure regulator. Stable flow rates will not be achieved by omitting the needle valve 
restrictor and attempting to adjust the rate with the pressure regulator alone.


cheers
Ritchie Sims


On 1 Jun 2010 at 3:46, M.Piranian wrote:

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*
Wouldn't it be easier and more accurate to take the tank volume, divide by the number of 
P10 spectrometers and the time the tank lasts. That eliminates bubble size uncertainty.
mp

--- On Mon, 5/31/10, Straszheim, Warren E [M S E] <[log in to unmask]> wrote:

From: Straszheim, Warren E [M S E] <[log in to unmask]>
Subject: Re: [PROBE-USERS] What's your P10 flow rate range?
To: [log in to unmask]
Date: Monday, May 31, 2010, 9:53 AM

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Moderator: Ellery Frahm, [log in to unmask], Electron Microprobe Lab, University of 
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*
FWIW, I recall 20 drops per milliliter for water. I don't how bubbles correspond to ml. I would 
set the flow and run it into an inverted, water-filled graduated cylinder. Supposing a bubble is 
equivalent to a drop, then 2 bubbles per second would be 120 per minute or 6 ml/min. That 
ain't much. I would doubt that you could find a rotameter reading that low, but I could be 
wrong. Personally, the tube in liquid seems good and simple and cheap enough for me. 

Warren S. 


From: JEOL-Focused Probe Users List [[log in to unmask]] On Behalf Of Steven 
Cogswell [[log in to unmask]]
Sent: Monday, May 31, 2010 8:27 AM
To: [log in to unmask]
Subject: [PROBE-USERS] What's your P10 flow rate range?
JEOL Probe Users Listserver 
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* Hi Probe folks;

I'm back again, but amazingly this time it's not because I have a technical problem. This time 
it's just an easy question.

Our JEOL 733 uses some P10 gas-flow spectrometers. We have the P10 tank hooked up to 
it and use one of those little "flow meters", as JEOL calls them, to see what the flow rate 
through the spectrometer is. Manual says "1-2 bubbles per second" when the little glass 
thingie (technical term) has alcohol in it.

I'm ambitious to replace the valve we use now to control the flow (very coarse, very crude) 
with an actual useful rotameter. Problem is, I have no clue what range I should buy. If I 
creak back to my old chemistry days usually they told you things like "1 drop is about 1 mL". 
Rotameters are expensive and I'd like to buy one with a correct range and not be 
disappointed.

So for folks who actually know what the gas flow rate is, what are you using? 


Best regards,
Steven Cogswell