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John et al:<br>
<br>
I am also a big believer in excess-flow switches and RFOs in
virtually all cylinders. We typically select a 0.010" RFO unless
there is a good reason to go larger or smaller. It is normally
installed by the gas supplier in the cylinder valve before it ever
shows up at our site ... although we do try to confirm that the
proper RFO has been installed before we install it. However, I'm a
bit confused by the comment about setting the excess-flow sensor
ABOVE the flow rate allowed by the orifice .... maybe I'm guilty of
the mistake that you are describing. If the excess flow switch is
downstream of the RFO (which it is in all cases for us), doesn't
that mean that the excess flow switch would never trip if it is set
higher than the RFO-limited flow (at least under steady-flow
conditions)? We typically try to size our excess flow switch so
that it will trip at a flow that is 2-3 times higher than the
maximum expected flow but that is typically several times LOWER than
the RFO-limited flow (at least at full cylinder pressure). For most
of our gases, we would likely have excess flow switches set to trip
at 6-10 SLM. Am I off the mark?<br>
<br>
More directly related to the hydrogen discussion, we've recently
changed our hydrogen sensors from LEL to 0-1000 ppm. While I
believe that the legal requirement is to detect a leak that reaches
25% LEL, all of our hydrogen sensors are now set to give us a
warning at 200 ppm and an alarm at 400 ppm. Our thinking is that we
are better off catching a leak as early as possible, since small
leaks seem to have a way of becoming large leaks.<br>
<br>
My apologies to all for not staying on the topic of H2 generators
... but whether coming from cylinders, generators, or a bulk
cryogenic source, safe handling and distribution of H2 is important
to us all.<br>
<br>
Thanks,<br>
<br>
John<br>
<br>
On 7/20/2012 5:51 AM, Weaver, John R wrote:
<blockquote
cite="mid:18AD986E445FE847B2A80B53E65704EDC8B0F01805@VPEXCH02.purdue.lcl"
type="cite"><span style="color: rgb(31, 73, 125);">I’m also a
believer in excess-flow sensors and fixed orifices. It seems
obvious (but I have seen this mistake), but the excess-flow
sensor must be set above the flow rate allowed by the orifice </span><span
style="font-family: Wingdings; color: rgb(31, 73, 125);">J</span><span
style="color: rgb(31, 73, 125);">.</span></blockquote>
<br>
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