<html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=us-ascii">
<meta name="Generator" content="Microsoft Word 14 (filtered medium)">
<!--[if !mso]><style>v\:* {behavior:url(#default#VML);}
o\:* {behavior:url(#default#VML);}
w\:* {behavior:url(#default#VML);}
.shape {behavior:url(#default#VML);}
</style><![endif]--><style><!--
/* Font Definitions */
@font-face
{font-family:Wingdings;
panose-1:5 0 0 0 0 0 0 0 0 0;}
@font-face
{font-family:Wingdings;
panose-1:5 0 0 0 0 0 0 0 0 0;}
@font-face
{font-family:Calibri;
panose-1:2 15 5 2 2 2 4 3 2 4;}
@font-face
{font-family:Tahoma;
panose-1:2 11 6 4 3 5 4 4 2 4;}
@font-face
{font-family:Georgia;
panose-1:2 4 5 2 5 4 5 2 3 3;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0in;
margin-bottom:.0001pt;
font-size:12.0pt;
font-family:"Times New Roman","serif";
color:black;}
a:link, span.MsoHyperlink
{mso-style-priority:99;
color:blue;
text-decoration:underline;}
a:visited, span.MsoHyperlinkFollowed
{mso-style-priority:99;
color:purple;
text-decoration:underline;}
p.MsoAcetate, li.MsoAcetate, div.MsoAcetate
{mso-style-priority:99;
mso-style-link:"Balloon Text Char";
margin:0in;
margin-bottom:.0001pt;
font-size:8.0pt;
font-family:"Tahoma","sans-serif";
color:black;}
span.EmailStyle17
{mso-style-type:personal;
font-family:"Calibri","sans-serif";
color:#1F497D;}
span.BalloonTextChar
{mso-style-name:"Balloon Text Char";
mso-style-priority:99;
mso-style-link:"Balloon Text";
font-family:"Tahoma","sans-serif";
color:black;}
span.EmailStyle20
{mso-style-type:personal-reply;
font-family:"Calibri","sans-serif";
color:#1F497D;}
.MsoChpDefault
{mso-style-type:export-only;
font-size:10.0pt;}
@page WordSection1
{size:8.5in 11.0in;
margin:1.0in 1.0in 1.0in 1.0in;}
div.WordSection1
{page:WordSection1;}
--></style><!--[if gte mso 9]><xml>
<o:shapedefaults v:ext="edit" spidmax="1026" />
</xml><![endif]--><!--[if gte mso 9]><xml>
<o:shapelayout v:ext="edit">
<o:idmap v:ext="edit" data="1" />
</o:shapelayout></xml><![endif]-->
</head>
<body bgcolor="white" lang="EN-US" link="blue" vlink="purple">
<div class="WordSection1">
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Something to remember -
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">The trip point of the excess flow switch is a function of switch size and inlet pressure, so the location where you place it (before or after the regulator)
makes a difference. If you place the switch on the pigtail, size the switch so it won't trip when your bottle decays in pressure. Depending on range selected, a switch that is fine at 60 slpm when the cylinder is at 1000 psig, could trip at as little as 10
slpm if your cylinder pressure decays to 100 psig. Always size for the worst case scenario.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Best Regards,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Tom Britton<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Sales Manager<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:14.0pt;font-family:"Georgia","serif";color:#1F497D">Critical Systems, Inc.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">7000 W. Victory Road<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Boise, ID 83709<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Direct: 208-890-1417<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Shop: 877-572-5515<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:8.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><i><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><img width="365" height="49" id="Picture_x0020_1" src="cid:image003.png@01CD666D.0CFE1920"></span></i><i><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p></o:p></span></i></p>
<p class="MsoNormal"><span style="font-size:8.0pt;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><i><span style="color:#1F497D"><a href="http://www.criticalsystemsinc.com/"><span style="color:blue">www.criticalsystemsinc.com</span></a><o:p></o:p></span></i></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<div>
<div style="border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in">
<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext"> labnetwork-bounces@mtl.mit.edu [mailto:labnetwork-bounces@mtl.mit.edu]
<b>On Behalf Of </b>Weaver, John R<br>
<b>Sent:</b> Friday, July 20, 2012 7:35 AM<br>
<b>To:</b> labnetwork@mtl.mit.edu<br>
<b>Subject:</b> Re: [labnetwork] H2 Generators<o:p></o:p></span></p>
</div>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">John –<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">My addled brain said it backward! Yes, the flow rate allowed by the fixed orifice should be higher than the trip point of the excess-flow sensor. The key is
that you need to allow the sensor to trip in a downstream failure that causes excess flow while limiting the maximum allowable flow.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">My apologies to the group for my confusing remark!<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">John <o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<div>
<p class="MsoNormal"><b><i><span style="font-size:10.0pt;color:#1F497D">John R. Weaver<o:p></o:p></span></i></b></p>
<p class="MsoNormal"><b><i><span style="font-size:10.0pt;color:#1F497D">Facility Manager<o:p></o:p></span></i></b></p>
<p class="MsoNormal"><b><i><span style="font-size:10.0pt;color:#1F497D">Birck Nanotechnology Center<o:p></o:p></span></i></b></p>
<p class="MsoNormal"><b><i><span style="font-size:10.0pt;color:#1F497D">Purdue University<o:p></o:p></span></i></b></p>
<p class="MsoNormal"><b><i><span style="font-size:10.0pt;color:#1F497D">(765) 494-5494<o:p></o:p></span></i></b></p>
<p class="MsoNormal"><b><i><span style="font-size:10.0pt;color:#1F497D"><a href="mailto:jrweaver@purdue.edu">jrweaver@purdue.edu</a><o:p></o:p></span></i></b></p>
</div>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<div>
<div style="border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in">
<p class="MsoNormal" style="margin-left:.5in"><b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext"> John Shott
<a href="mailto:[mailto:shott@stanford.edu]">[mailto:shott@stanford.edu]</a> <br>
<b>Sent:</b> Friday, July 20, 2012 10:23 AM<br>
<b>To:</b> <a href="mailto:labnetwork@mtl.mit.edu">labnetwork@mtl.mit.edu</a>; John Weaver<br>
<b>Subject:</b> Re: [labnetwork] H2 Generators<o:p></o:p></span></p>
</div>
</div>
<p class="MsoNormal" style="margin-left:.5in"><o:p> </o:p></p>
<p class="MsoNormal" style="margin-left:.5in">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: <o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="color:#1F497D">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:#1F497D">J</span><span style="color:#1F497D">.</span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in"><o:p> </o:p></p>
</div>
</body>
</html>