<html><head><meta http-equiv="Content-Type" content="text/html charset=windows-1252"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">If it makes any difference, this is the gauge I have…..one of the liquid-filled ones on the top left:<div class=""><br class=""></div><div class=""><a href="http://www.mcmaster.com/#catalog/122/591/=13utw0q" class="">http://www.mcmaster.com/#catalog/122/591/=13utw0q</a></div><div class=""><br class=""></div><div class=""><br class=""></div><div class=""><br class=""></div><div class=""><br class=""><div><blockquote type="cite" class=""><div class="">On Aug 23, 2016, at 6:43 PM, Jim Adney <<a href="mailto:jadney@vwtype3.org" class="">jadney@vwtype3.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class="">On 23 Aug 2016 at 22:21, Max Welton wrote:<br class=""><br class=""><blockquote type="cite" class="">I think the FPR is composed of a spring, a diaphragm and a valve. Fuel<br class="">pressure exerts force to overcome the spring. Ambient air pressure is<br class="">not a factor in this. <br class=""></blockquote><br class="">The spring only about half the force needed in this case. The other <br class="">half is provided by the outside air pressure. So, in this case, <br class="">ambient air pressure IS a factor in this.<br class=""><br class=""><blockquote type="cite" class="">I would think the pressure gauge is also just a spring and a diaphragm.<br class=""></blockquote><br class="">Well, sort of, but there's really no spring in a typical gauge. If <br class="">you put a typical pressure gauge in a pressure chamber, it will also <br class="">read just the difference between the chamber pressure and the <br class="">"measured" pressure. It will show the pressure difference.<br class=""><br class="">That certainly makes this problem harder, since you're trying to <br class="">compensate for both the change in the gauge and the change in the <br class="">fuel pressure regulator. The fact that there is a spring in the <br class="">regulator but there isn't in the gauge means that the two errors <br class="">don't cancel out.<br class=""><br class="">I'll have to think about this some more....<br class=""><br class="">-- <br class="">*******************************<br class="">Jim Adney, <a href="mailto:jadney@vwtype3.org" class="">jadney@vwtype3.org</a><br class="">Madison, Wisconsin, USA<br class="">*******************************<br class=""><br class="">_______________________________________________<br class=""><a href="http://VWType3.Org" class="">VWType3.Org</a> mailing list - <a href="mailto:type3@vwtype3.org" class="">type3@vwtype3.org</a><br class="">To unsubscribe or change subscription options, visit:<br class=""><a href="http://lists.vwtype3.org/listinfo.cgi/type3-vwtype3.org" class="">http://lists.vwtype3.org/listinfo.cgi/type3-vwtype3.org</a><br class="">If you need more help, contact: gregm@vwtype3.org<br class=""></div></blockquote></div><br class=""></div></body></html>