Facet fuel pumps do restrict the flow, and the funny thing is they don't do it evenly. It actually depends on which position the pump plate has when it stops.
It's another of these crazy aircraft situations: we use Facets because they are approved by the FAA, and they are approved by the FAA because they have internal bypass... but that internal bypass does restrict the flow considerably. My new engine does not have an engine driven pump, so I installed a single Facet, hoping to get free flow through it. Result: the flow would hardly keep the engine idle when the header tank is low. So, I ordered a nonreturn valve from ASS, and made a bypass. Only to find that gravity from the header is not enough to open the valve. I don't consider two Facets a good option, because you would then have to design a way to detect a failure, so it is more complexity, more weight... and bad practice too. Also, electrical failure becomes critical. So, I will end up making a free bypass around the Facet. I will use two T-junctions, set so as to favor the free flow in, and the Facet out. This way, probably gravity will prevail. The Facet will pump more than enough fuel anyway, so if the loop induces a loss (pumping in circle), well, so be it. If I had time to redo the system, I would go to the nearest junkyard, get hold of a good fuel pump from a reputable Japanese or German made car, and bypass it with large section free flow piping. Bottom line: Facets suck... badly! Serge Vidal Paris, France "Brian Kraut" <[email protected]> Envoyé par : [email protected] 2004-11-13 03:23 Veuillez répondre à KRnet Remis le : 2004-11-13 03:20 Pour : "KRnet" <[email protected]> cc : (ccc : Serge VIDAL/DNSA/SAGEM) Objet : RE: KR> Facet #40108 Another thing or two to keep in mind when designing fuel systems with the Facet pumps. You shoud have the pump mounted low in the system if possible. I had one mounted on the back of my header tank to transfer fuel from the wings to the header. I did some experimenting first to see if the pump would suck up fuel through a dry line from up that high and it worked fine. In operation a few times after it was installed it refused to suck a prime through the line. A good slip with the wing of the selected tank high would usually be enough to get a prime sucked in the line and start it pumping normally, but mounting the pump lower would be a lot better. The Facet pumps restrict the fuel flow some when not running. I put one on my firewall as a boost pump for the header tank and found that it restricted fuel flow enough when it was not running that I couldn't throtle past half before the engine would start coughing. I measured the fuel flow and then removed the pump and increase the flow by over double what it was going through the pump when it was not running. Keep the odd shortcomings in mind and the pumps work very good. Brian Kraut Engineering Alternatives, Inc. www.engalt.com _______________________________________ to UNsubscribe from KRnet, send a message to [email protected] please see other KRnet info at http://www.krnet.org/info.html
