X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Thu, 14 Jun 2007 20:39:59 -0400 Message-ID: X-Original-Return-Path: Received: from pan.gwi.net ([207.5.128.165] verified) by logan.com (CommuniGate Pro SMTP 5.1.9) with ESMTPS id 2103295 for lml@lancaironline.net; Thu, 14 Jun 2007 19:58:31 -0400 Received-SPF: pass receiver=logan.com; client-ip=207.5.128.165; envelope-from=dhc1@gwi.net Received: from S0032744976 (d-216-195-153-76.gwi.net [216.195.153.76]) by pan.gwi.net (8.13.1/8.13.1) with SMTP id l5ENvmeq059861 for ; Thu, 14 Jun 2007 19:57:50 -0400 (EDT) (envelope-from dhc1@gwi.net) X-Original-Message-ID: <007f01c7aedf$ceec2130$0500000a@S0032744976> From: "Bill Wade" X-Original-To: "Lancair Mailing List" References: Subject: Re: [LML] Re: Boost Pump X-Original-Date: Thu, 14 Jun 2007 19:57:46 -0400 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_007C_01C7AEBE.473BA920" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.3138 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.3138 This is a multi-part message in MIME format. ------=_NextPart_000_007C_01C7AEBE.473BA920 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable I'm not sure that I could scan the diagrams successfully so I'll try = my best to describe them. Looking at the fuel system schematic (2-15 of the TSIO-550 Maintenance = & Overhaul Manual), fuel from the tank goes through the boost pump, then = the vapor separator, then into the engine driven pump. Boost pump flow = can bypass the engine driven via a check valve. The engine-driven pump = output is regulated by engine speed; also by an idle pressure relief = valve, an aneroid full power valve, and by the mixture control. The last = three items work by recirculating fuel to the inlet side of the pump. = The fuel return to the tank is located between the pump output and the = mixture control. Fuel from the boost pump is also shown as flowing = through the pump outlet, before the fuel return. The mixture control is = the last point in the system to remove excess fuel. After that it goes = through the throttle body where it is metered, then on to the spider. I also have a small TCM manual that describes the injection system. It = states that the pump has excess capacity so that pressure can be = maintained at all speeds through the use of a calibrated orifice and = relief valve in a recirculation loop. I assume that's for non-aneroid = pumps. The unmetered fuel pressure (between the pump and the throttle body) = for the E is 7.0-9.0 PSI at idle and goes to 32-36 full throttle. Full = throttle flow is 245-255 lbs/hr (roughly 41-42 GPH). I'm looking at a Dukes pump that's rated 11.0 PSI low and 25 PSI on = high. Flow rate is 35 GPM @ 21.0 PSI. I don't know how this compares to = the pumps being used in Lancair installations, but wouldn't seem that = the Dukes could overload the system, especially if the engine-driven = pump was inoperative. If you were idling and hit the high boost, yes. At = full TO power it should be less than the engine-driven output. My = question is: could the output of the two pumps combine and overwhelm the = return line causing pressure and thus fuel flow to go out of limits? It seems to me that the biggest concern is at takeoff. At altitude = there would be time to restart. The installations on my planes (TCM = IO-360, IO-550B) use a ceramic resistor for the low side. Would there be = a way to vary resistance to the high side to keep output of the boost = pump within tolerance even if the high setting was selected by accident? BTW, I don't use low boost on takeoff. Some manuals recommend it, but = to me it's one more thing to remember and I've operated that way for = 1,000 hours with no problem. The only time I had a problem was when I = forgot to turn the boost off after startup! Rough idle, low power and a = lot of smoke. -Bill Wade ----- Original Message -----=20 From: Craig Berland=20 To: lml@lancaironline.net=20 Sent: Thursday, June 14, 2007 10:50 AM Subject: [LML] Re: Boost Pump Kevin wrote:=20 Is it safe to assume then that the fuel return line isn't able to = return all the fuel that isn't being used? Maybe there are restrictions = in the return line that prevents fuel from retuning at a flow rate that = would prevent it from also bypassing the mechanical pump? =20 Or does the return line start after the bypass value for the = mechanical pump? =20 =20 There is a variable orifice as well as the bypass valve involved in = the fuel return system that will affect fuel rate beyond the return line = size. To get fuel injection to work somewhat automatically with a pure = mechanical system is very difficult. Adding a turbo further complicates = the effort. Having a mixture knob controlled by the pilot is a big = deal. A good deal if properly controlled. My advise is to be very = careful when trying to modify the way the mechanical fuel injection = system meters fuel. VERY simply put, the pressure at the injector = controls the fuel rate. Increasing the inlet fuel pressure at the = mechanical engine driven pump will increase the fuel rate. Let me give = you some food for thought. The increased fuel rate caused by turning on = the high boost pump may be acceptable to the engine during the winter = months in Minnesota but will the same fuel rate increase be acceptable = to the engine today in Arizona (110 def F). In my opinion high boost on = the TSIO550 should be used for aid in starting and as a back-up in case = of a mechanical engine driven fuel pump failure only. Craig Berland ------=_NextPart_000_007C_01C7AEBE.473BA920 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
  I'm not sure that I could = scan the=20 diagrams successfully so I'll try my best to describe = them.
  Looking at the fuel system = schematic=20 (2-15 of the TSIO-550 Maintenance & Overhaul Manual), fuel from the = tank=20 goes through the boost pump, then the vapor separator, then into the = engine=20 driven pump. Boost pump flow can bypass the engine driven via a check = valve. The=20 engine-driven pump output is regulated by engine speed; also by an = idle=20 pressure relief valve, an aneroid full power valve, and by the = mixture=20 control. The last three items work by recirculating fuel to the inlet = side of=20 the pump. The fuel return to the tank is located between the pump = output=20 and the mixture control. Fuel from the boost pump is also shown as = flowing=20 through the pump outlet, before the fuel return. The mixture control is = the last=20 point in the system to remove excess fuel. After that it goes through = the=20 throttle body where it is metered, then on to the spider.
  I also have a small TCM manual = that=20 describes the injection system. It states that the pump has excess = capacity so=20 that pressure can be maintained at all speeds through the use of a = calibrated=20 orifice and relief valve in a recirculation loop. I assume that's for=20 non-aneroid pumps.
  The unmetered fuel pressure = (between the=20 pump and the throttle body) for the E is 7.0-9.0 PSI at idle and = goes to=20 32-36 full throttle. Full throttle flow is 245-255 lbs/hr (roughly 41-42 = GPH).
  I'm looking at a Dukes pump = that's rated=20 11.0 PSI low and 25 PSI on high. Flow rate is 35 GPM @ 21.0 PSI. I = don't=20 know how this compares to the pumps being used in Lancair installations, = but=20 wouldn't seem that the Dukes could overload the system, especially = if  the=20 engine-driven pump was inoperative. If you were idling and hit the high = boost,=20 yes. At full TO power it should be less than the engine-driven output. = My=20 question is: could the output of the two pumps combine and overwhelm the = return=20 line causing pressure and thus fuel flow to go out of = limits?
 It seems to me that the biggest = concern is at=20 takeoff. At altitude there would be time to restart. The = installations on=20 my planes (TCM IO-360, IO-550B) use a ceramic resistor for the = low=20 side. Would there be a way to vary resistance to the high side = to keep=20 output of the boost pump within tolerance even if the high setting was = selected=20 by accident?
 BTW, I don't use low boost on = takeoff. Some=20 manuals recommend it, but to me it's one more thing to remember and = I've=20 operated that way for 1,000 hours with no problem. The only time I had a = problem=20 was when I forgot to turn the boost off after startup! Rough idle, = low=20 power and a lot of smoke. -Bill Wade
----- Original Message -----
From:=20 Craig=20 Berland
Sent: Thursday, June 14, 2007 = 10:50=20 AM
Subject: [LML] Re: Boost = Pump

 

Kevin =20 wrote: 

Is it safe = to assume=20 then that the fuel return line isn=92t able to return all the fuel = that isn=92t=20 being used?  Maybe there are restrictions in the return line that = prevents fuel from retuning at a flow rate that would prevent it from = also=20 bypassing the mechanical pump?

 

Or does the = return=20 line start after the bypass value for the mechanical=20 pump?

 

 

 There is a variable = orifice as=20 well as the bypass valve involved in the fuel return system that will = affect=20 fuel rate beyond the return line size.  To get fuel injection to = work=20 somewhat automatically with a pure mechanical system is very = difficult. =20 Adding a turbo further complicates the effort.  Having a mixture = knob=20 controlled by the pilot is a big deal.  A good deal if properly=20 controlled.  My advise is to be very careful when trying to = modify the=20 way the mechanical fuel injection system meters fuel.  VERY = simply put,=20 the pressure at the injector controls the fuel rate.  Increasing = the=20 inlet fuel pressure at the mechanical engine driven pump will increase = the=20 fuel rate.  Let me give you some food for thought.  The = increased=20 fuel rate caused by turning on the high boost pump may be acceptable = to the=20 engine during the winter months in Minnesota but will the same fuel = rate=20 increase be acceptable to the engine today in Arizona (110 def = F).  In my=20 opinion high boost on the TSIO550 should be used for aid in starting = and as a=20 back-up in case of a mechanical engine driven fuel pump failure=20 only.

Craig=20 Berland

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