Return-Path: Received: from mail13.syd.optusnet.com.au ([211.29.132.194] verified) by logan.com (CommuniGate Pro SMTP 4.3c2) with ESMTP-TLS id 753415 for flyrotary@lancaironline.net; Mon, 21 Feb 2005 17:57:48 -0500 Received-SPF: none receiver=logan.com; client-ip=211.29.132.194; envelope-from=lendich@optusnet.com.au Received: from george (d211-31-92-201.dsl.nsw.optusnet.com.au [211.31.92.201]) by mail13.syd.optusnet.com.au (8.12.11/8.12.11) with SMTP id j1LMuxUB019624 for ; Tue, 22 Feb 2005 09:57:01 +1100 Message-ID: <008201c51868$fd3e9690$c95c1fd3@george> From: "George Lendich" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Re: For Todd "Vena Contracta" was Re: Returnless Fuel System - Fuel Cooler Date: Tue, 22 Feb 2005 08:59:24 +1000 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_007F_01C518BC.CE54F640" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2800.1106 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 This is a multi-part message in MIME format. ------=_NextPart_000_007F_01C518BC.CE54F640 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable RE: [FlyRotary] Returnless Fuel System - Fuel CoolerTodd, A good explanation, certainly better than I could give, but I understood = your original post as it seemed intuitive to me. Thanks for the heads-up on back pressure and pump cavitation - I didn't = think of that one! All the best for the exams! George ( down under) Hi Leon; I'm a little late responding as I spent the weekend rebuilding my = dirt bike with one of them ole fashioned piston engines what go up & = down to make something go round 'n round? What a goofy idea! Anyways, back to the subject at hand. Pressure recovery ?... so = what? Well without pressure differential there is no flow. None. I = realize that jets are used to meter flow and that a restriction is an = impediment to flow, however my point was that if the EFI pump has an = outlet of say 1/8" into a 3/8" line (or in Bob's case, his 1/4" return = line) it does not have the equivalent flow of a 1/8" line. While it will = not have full flow of an unrestricted line due to permanent pressure = loss, it will recover much of its pressure resulting in a much greater = flow than would be provided by a 1/8" tube. To calculate this the Beta = ratio of the "orifice" is required, however it really isn't that = important. Besides, I can't find right now the required formula. I = should get back to studying this as I return to school for 4th year in 2 = months and I can be assured that there will be at least one twisted = question concerning this on the incoming exam. Someone had mentioned drilling out the pump outlet to reduce this = restriction, but that would be a really bad idea. The pump outlet is = usually sized smaller than the pipe that it is sized for in order to = provide adequate back pressure to the pump to prevent cavitation. If you = drill out this outlet, then bubbles can/will form in the impellor and = the resulting cavitation will result in less flow and quite possibly the = vapour lock that we are trying to avoid. This restriction does not = diminish the requirement for a proper sized tube to be plumbed to it in = order to achieve rated flow. Just my 2 bits worth Cheers Todd So I just can't see what the size of an attached pipe has to do with = the flow rate through a "vena contracta" ("vena constricta"??). You = also say "but much of this pressure is recovered downstream" Hmmmmmm, = ... I say "so what"??. We aren't interested in pressure drops or = pressure recovery, ... it's flow rates that are the SOLE issue, and the = capacity of an open flow 1/4 inch line to get rid of the fuel dumped by = the regulator. =20 Leon ------=_NextPart_000_007F_01C518BC.CE54F640 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable RE: [FlyRotary] Returnless Fuel System - Fuel = Cooler
Todd,
A good explanation, certainly better = than I could=20 give, but I understood your original post as it seemed intuitive to=20 me.
Thanks for the heads-up on back = pressure and pump=20 cavitation - I didn't think of that one!
All the best for the = exams!
George ( down under)
Hi Leon;
   =20 I'm a little late = responding as I spent=20 the weekend rebuilding my dirt bike with one of them ole fashioned = piston=20 engines what go up & down to make something go round 'n round? = What a=20 goofy idea!
   =20 Anyways, back to the = subject at hand.=20 Pressure recovery ?... so what? Well without pressure = differential there=20 is no flow. None. I realize that jets are used to meter flow and that = a=20 restriction is an impediment to flow, however my point was that if the = EFI=20 pump has an outlet of say 1/8" into a 3/8" line (or in Bob's case, his = 1/4"=20 return line) it does not have the equivalent flow of a 1/8" line. = While=20 it will not have full flow of an unrestricted line due to = permanent=20 pressure loss, it will recover much of its pressure resulting in = a much=20 greater flow than would be provided by a 1/8" tube. To calculate this = the Beta=20 ratio of the "orifice" is required, however it really isn't that = important.=20 Besides, I can't find right now the required formula. I should get = back to=20 studying this as I return to school for 4th year in 2 months and I can = be=20 assured that there will be at least one twisted question concerning = this on=20 the incoming exam.
   =20 Someone had mentioned = drilling out the=20 pump outlet to reduce this restriction, but that would be a really bad = idea.=20 The pump outlet is usually sized smaller than the pipe that it is = sized for in=20 order to provide adequate back pressure to the pump to prevent = cavitation. If=20 you drill out this outlet, then bubbles can/will form in the impellor = and the=20 resulting cavitation will result in less flow and quite possibly the = vapour=20 lock that we are trying to avoid. This restriction does not diminish = the=20 requirement for a proper sized tube to be plumbed to it in order to = achieve=20 rated flow.
   =20 Just my 2 bits = worth
Cheers
Todd

So I just can't see what the = size of an=20 attached pipe has to do with the flow rate through a  "vena = contracta"=20 ("vena constricta"??).  You also say "but much of this pressure = is=20 recovered downstream"  Hmmmmmm, ... I say "so what"??.  We = aren't=20 interested in pressure drops or pressure recovery, ... it's = flow rates=20 that are the SOLE issue,  and the capacity of an open=20 flow 1/4 inch line to get rid of the fuel dumped by the=20 regulator. 
 
 
Leon =20
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