Return-Path: Received: from imf22aec.mail.bellsouth.net ([205.152.59.70] verified) by logan.com (CommuniGate Pro SMTP 4.3c1) with ESMTP id 727118 for flyrotary@lancaironline.net; Sun, 13 Feb 2005 09:00:55 -0500 Received-SPF: pass receiver=logan.com; client-ip=205.152.59.70; envelope-from=sqpilot@bellsouth.net Received: from [209.214.44.221] by imf22aec.mail.bellsouth.net (InterMail vM.5.01.06.11 201-253-122-130-111-20040605) with ESMTP id <20050213140007.EVRY730.imf22aec.mail.bellsouth.net@[209.214.44.221]> for ; Sun, 13 Feb 2005 09:00:07 -0500 Received: from 127.0.0.1 (AVG SMTP 7.0.300 [265.8.7]); Sun, 13 Feb 2005 08:00:05 -0600 Message-ID: <01ae01c511d4$5035f6e0$dd2cd6d1@paul52u7f5qyav> From: "Paul" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Re: Vapor Lock Date: Sun, 13 Feb 2005 08:00:02 -0600 X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.2180 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2180 Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="=======AVGMAIL-420F5D655060=======" --=======AVGMAIL-420F5D655060======= Content-Type: multipart/alternative; boundary="----=_NextPart_000_01AB_01C511A2.0572F040" ------=_NextPart_000_01AB_01C511A2.0572F040 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable Hi, Al....I did not find your post to be long or boring....you have done = a fine job of addressing potential fuel problems and possible remedies. = I learned more from this post than I was able to obtain from the = aircraft construction manual, for sure. Thanks for taking the time to = put it together. Paul, needavent Conner ----- Original Message -----=20 From: Al Gietzen=20 To: Rotary motors in aircraft=20 Sent: Saturday, February 12, 2005 1:18 PM Subject: [FlyRotary] Re: Vapor Lock This issue has been worked over pretty thoroughly, but bear with me = through some comments and possible clarifications if this subject has = your interest. 1.) In general I don't think it is ever a good idea to expect fuel, = particularly mogas, to be "sucked". The ability to draw any liquid is = limited by its vapor pressure, the pressure at which it will flash to = vapor rather to remain as a liquid. Even water at room temp can only be = sucked to a head of about 30 ft (about 14 psi) beyond which it will be = vapor. At the boiling point, obviously it can't be lifted or drawn at = all, all you get is vapor. Auto fuel at room temp can only be drawn to = something like a 6 ft head, less than 2 psi, or it will flash to vapor. = Increase its temp a bit and pretty soon you can't suck it at all; all = you get is vapor. So any system in which you expect to apply negative = pressure to move the fuel is at risk. It may work fine at normal temps, = but when it warms up, look out. 2.) As a corollary to this, in a gravity fed system it is not a good = idea to have a fuel filter (or even gascolator with a fine screen) = upstream from the EFI pump, because it causes restriction to flow, = especially after it has picked up some dirt. Yes; you do not want any = water getting through the pump, and one good reason for having a sump or = header tank is the have the exit to the EFI pump above the bottom so any = water and dirt will be collected, and be drained with a sample drain. = If an upstream filter or gascolator is in the engine compartment, so = much the worse, because it causes a dwell time in a hot place for the = fuel to heat. To draw it from there to the pump, as in Paul's case, can = be a setup for vapor lock. 3.) Normally you want the fuel to recirc through the fuel rail, with = the pressure regulator bypass going back to some tank upstream from the = EFI pump; the reasons all relate to keeping down the temp of the fuel to = the fuel rail. As Leon points out, it is has been the proven way. Yes, = you can plumb a one-way path from between the pump and the regulator to = the fuel rail so only fuel burned by the engine goes to the engine = compartment, and normally it may work fine, but the residence time of = the fuel in the hot environment can result in very high fuel temps. It = can cause variation in performance depending on the temp as the density = of the fuel varies. Even though the pressure downstream from the EFI = pump significantly reduces the likelihood of vapor forming; I don't know = how hot the fuel would need to get to boil at 40 psi; I can imagine the = case after engine shutdown on a hot day that won't restart because the = fuel in the line and rail have filled with vapor; possibly bleeding back = through the pump. 4.) The bypass fuel return from the pressure regulator can indeed be = under pressure if it is restricted. The regulator produces a = differential pressure across a restriction. If you restrict the bypass = flow (back pressure) the pressure in the fuel rail will increase, = possibly up to the limit of the pump. So in John's case it is to be = expected that if the tank the return fuel is going to is full, the = engine will lose power because the mixture will get very rich. 5.) It seems to me the sump/header tank must be vented in some way = to allow air/vapor return to the main tank, or out. There can be = different circumstances for different configurations. The case that Jim = mentions for not having the vent in a gravity feed system is to overcome = a specific issue of loss of flow due to tank cap leaks which caused the = low pressure above the wing (strake) to offset the rather small gravity = pressure head. His solution of a controlled vent is a good one, unless = you are confident that your caps will always be leaktight. 6.) Whether or not the Paul's sump tank became full of vapor is not = known, but a vent is needed. The vent line must extend upward to a level = above the level of the fuel in the main tanks before going down and out = to avoid fuel being lost overboard. It is also important that the vent = lines from the main tanks and the sump tank go off the highest point in = the tank. If the exit is submerged, expanding fuel can result in fuel = going overboard.=20 Ok; this got longer and maybe more boring than I had hoped, but like = everyone else, I'm trying to be helpful. Al Subject: [FlyRotary] Vapor Lock Hi, Perry....One question....Does your unburned fuel (from the fuel = rail) go back into your sump tank also? Or do you return the unused = fuel to one of your fuel tanks? If I were returning fuel to one of the = main tanks, I would think that venting the sump would be appropriate, = but since I am sending fuel undere pressure back into the sump tank, I = am concerned that once the sump tank is full, the additional fuel pumped = back into the sump tank would take the path of least resistance....out = the vent instead of back up the fuel line into the tank? Thanks for = your input. Paul Conner One other comment Paul: the fuel return from the fuel rail is not = pressurized. The pressure regulator maintains HP on the fuel rail side, = but the fuel return output back to the sump is not under high pressure. -------------------------------------------------------------------------= ----- No virus found in this incoming message. Checked by AVG Anti-Virus. Version: 7.0.300 / Virus Database: 265.8.7 - Release Date: 2/10/2005 ------=_NextPart_000_01AB_01C511A2.0572F040 Content-Type: text/html; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable
Hi, Al....I did not find your post to = be long or=20 boring....you have done a fine job of addressing potential fuel problems = and=20 possible remedies. I learned more from this post than I was able to = obtain from=20 the aircraft construction manual, for sure.  Thanks for taking the = time to=20 put it together.   Paul, needavent Conner
----- Original Message -----
From:=20 Al = Gietzen=20
Sent: Saturday, February 12, = 2005 1:18=20 PM
Subject: [FlyRotary] Re: Vapor = Lock

This issue has been = worked over=20 pretty thoroughly, but bear with me through some comments and possible = clarifications if this subject has your interest.

 

1.) =20 In general I don=92t = think it is=20 ever a good idea to expect fuel, particularly mogas, to be = =93sucked=94.  The=20 ability to draw any liquid is limited by its vapor pressure, the = pressure at=20 which it will flash to vapor rather to remain as a liquid.  Even = water at=20 room temp can only be sucked to a head of about 30 ft (about 14 psi) = beyond=20 which it will be vapor. At the boiling point, obviously it can=92t be = lifted or=20 drawn at all, all you get is vapor.  Auto fuel at room temp can = only be=20 drawn to something like a 6 ft head, less than 2 psi, or it will flash = to=20 vapor.  Increase its temp a bit and pretty soon you can=92t suck = it at all;=20 all you get is vapor.  So any system in which you expect to apply = negative pressure to move the fuel is at risk.  It may work fine = at=20 normal temps, but when it warms up, look out.

 

2.) =20 As a corollary to = this, in a=20 gravity fed system it is not a good idea to have a fuel filter (or = even=20 gascolator with a fine screen) upstream from the EFI pump, because it = causes=20 restriction to flow, especially after it has picked up some dirt. Yes; = you do=20 not want any water getting through the pump, and one good reason for = having a=20 sump or header tank is the have the exit to the EFI pump above the = bottom so=20 any water and dirt will be collected, and be drained with a sample=20 drain.  If an upstream filter or gascolator is in the engine = compartment,=20 so much the worse, because it causes a dwell time in a hot place for = the fuel=20 to heat. To draw it from there to the pump, as in Paul=92s case, can = be a setup=20 for vapor lock.

 

3.) =20 Normally you want the = fuel to=20 recirc through the fuel rail, with the pressure regulator bypass going = back to=20 some tank upstream from the EFI pump; the reasons all relate to = keeping down=20 the temp of the fuel to the fuel rail.  As Leon=20 points out, it is has been the proven way.  Yes, you can plumb a = one-way=20 path from between the pump and the regulator to the fuel rail so only = fuel=20 burned by the engine goes to the engine compartment, and normally it = may work=20 fine, but the residence time of the fuel in the hot environment can = result in=20 very high fuel temps.  It can cause variation in performance = depending on=20 the temp as the density of the fuel varies. Even though the pressure=20 downstream from the EFI pump significantly reduces the likelihood of = vapor=20 forming; I don=92t know how hot the fuel would need to get to boil at = 40 psi; I=20 can imagine the case after engine shutdown on a hot day that won=92t = restart=20 because the fuel in the line and rail have filled with vapor; possibly = bleeding back through the pump.

 

4.) =20 The bypass fuel return = from the=20 pressure regulator can indeed be under pressure if it is = restricted.  The=20 regulator produces a differential pressure across a restriction.  = If you=20 restrict the bypass flow (back pressure) the pressure in the fuel rail = will=20 increase, possibly up to the limit of the pump.  So in John=92s = case it is=20 to be expected that if the tank the return fuel is going to is full, = the=20 engine will lose power because the mixture will get very=20 rich.

 

5.)   =20 It seems to me the = sump/header=20 tank must be vented in some way to allow air/vapor return to the main = tank, or=20 out.  There can be different circumstances for different=20 configurations.  The case that Jim mentions for not having the = vent in a=20 gravity feed system is to overcome a specific issue of loss of flow = due to=20 tank cap leaks which caused the low pressure above the wing (strake) = to offset=20 the rather small gravity pressure head.  His solution of a = controlled=20 vent is a good one, unless you are confident that your caps will = always be=20 leaktight.

 

6.)   =20 Whether or not the = Paul=92s sump=20 tank became full of vapor is not known, but a vent is needed. The vent = line=20 must extend upward to a level above the level of the fuel in the main = tanks=20 before going down and out to avoid fuel being lost overboard. It is = also=20 important that the vent lines from the main tanks and the sump tank go = off the=20 highest point in the tank. If the exit is submerged, expanding fuel = can result=20 in fuel going overboard.

 

Ok; this got longer = and maybe=20 more boring than I had hoped, but like everyone else, I=92m trying to = be=20 helpful.

 

Al

 

 

 

 

 

Subject:=20 [FlyRotary] Vapor Lock

 

Hi, Perry....One = question....Does=20 your unburned fuel (from the fuel rail) go back into your sump tank=20 also?   Or do you return the unused fuel to one of your fuel = tanks?  If I were returning fuel to one of the main tanks, I = would think=20 that venting the sump would be appropriate, but since I am sending = fuel undere=20 pressure back into the sump tank, I am concerned that once the sump = tank is=20 full, the additional fuel pumped back into the sump tank would take = the path=20 of least resistance....out the vent instead of back up the fuel line = into the=20 tank?   Thanks for your input.  Paul = Conner

One other comment Paul: = the fuel=20 return from the fuel rail is not pressurized. The pressure regulator = maintains=20 HP on the fuel rail side, but the fuel return output back to the sump = is not=20 under high pressure.

No virus found in this incoming message.
Checked by AVG=20 Anti-Virus.
Version: 7.0.300 / Virus Database: 265.8.7 - Release = Date:=20 2/10/2005
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