X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from fmailhost03.isp.att.net ([207.115.11.53] verified) by logan.com (CommuniGate Pro SMTP 5.4.5) with ESMTP id 5598425 for flyrotary@lancaironline.net; Wed, 13 Jun 2012 22:07:38 -0400 Received-SPF: none receiver=logan.com; client-ip=207.115.11.53; envelope-from=bbradburry@bellsouth.net Received: from desktop (adsl-98-85-143-88.mco.bellsouth.net[98.85.143.88]) by isp.att.net (frfwmhc03) with SMTP id <20120614020701H0300cp5v3e>; Thu, 14 Jun 2012 02:07:01 +0000 X-Originating-IP: [98.85.143.88] From: "Bill Bradburry" To: "'Rotary motors in aircraft'" References: In-Reply-To: Subject: RE: [FlyRotary] Re: Two possible causes was : [FlyRotary] Re: Fuel presure question. Date: Wed, 13 Jun 2012 22:07:02 -0400 Message-ID: <96644D7AF123462096EA7EE2C4887F3F@Desktop> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0037_01CD49B0.DCAD9E90" X-Mailer: Microsoft Office Outlook 11 X-MimeOLE: Produced By Microsoft MimeOLE V6.0.6002.18463 Thread-Index: Ac1JxBisfvXfnt6JR9upGkhwzKM7VQADgM2w This is a multi-part message in MIME format. ------=_NextPart_000_0037_01CD49B0.DCAD9E90 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit David, If they don't, each pump should have its own circuit, otherwise you lose your redundancy. Bill B _____ From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Mark Steitle Sent: Wednesday, June 13, 2012 8:24 PM To: Rotary motors in aircraft Subject: [FlyRotary] Re: Two possible causes was : [FlyRotary] Re: Fuel presure question. David, Ed covered what I was thinking about a possible bad check-valve in one of your pumps. And a bunch of other stuff I hadn't considered. Mark On Wed, Jun 13, 2012 at 6:17 PM, Ed Anderson wrote: David, don't know whether you have considered this - as you are aware the two pumps are able to work in parallel because the pumps have check valves. So if one pump is off and the other on, the on pump does not pump fuel backwards through the off pump. Since each pump produces the 42 psi pressure by itself, one would assume the pumping elements in both pumps are working properly. Also assuming the pressure change is NOT due to a malfunctioning pressure sensor. Here are some things that you might want to consider: 1. That somehow when both pumps are on - one of the pumps check valves is not closing properly. Not a pump expert so not certain this could even happen - but the thought occurred to me. 2. The effect of Increased fuel flow rate due to both pumps may be causing a pressure drop through an upstream orifice (like perhaps your "T"). 3. Turning on both pumps (assuming on the same circuit) might cause sufficient voltage drop in the line sufficient to decrease the pumping performance of both pumps - pump flow rates are sensitive to voltage variations. 4. The pressure return regulator might be malfunctioning and opening due to the higher flow rate - easy to check, just temporarily block off the return. If the symptom disappears then it's the regulator. Theoretically, if the fuel flow rate through the T's and pumps does not change with both pumps on, then the pressure should remain the same - which is what you are expecting, but not seeing. So since the pressure does change (drops) - what could cause this (assuming the pressure drop is real and not the result some strange malfunction of your gauge)? One thing that could cause it, is if the fuel flow rate increases through an upstream orifice in your fuel line (say at the "T" which feeds your two pumps) then the pressure on the other (downstream) side will drop. Turn one of the pumps off, the fuel flow rate drops, therefore there is less pressure drop across this orifice and your fuel pressure on the downstream side of the orifice will again go up. Its similar to a resistor in a circuit. The resistor value will remain static - the same, but if you pull more current thought it, the voltage drop across it will increase resulting in less voltage on the downstream side. Reduce the current flow back to previous rate and the voltage drop across the resistor decreases and therefore voltage on the downstream side increase. Another possible cause might be if both of your pumps are fed off the same electrical line and there is sufficient resistance that when both pumps are on the voltage drop causes less performance by both pumps. Just some WAGs that you might consider, if the suggestions make by others do not result in identifying the cause. Good Luck Ed Edward L. Anderson Anderson Electronic Enterprises LLC 305 Reefton Road Weddington, NC 28104 http://www.andersonee.com http://www.eicommander.com From: hoursaway1@comcast.net Sent: Wednesday, June 13, 2012 6:43 PM To: Rotary motors in aircraft Subject: [FlyRotary] Re: Fuel presure question. Fuel is gravity routed from tanks to ganged fuel selector out to T-fitting with each pump on the sides of the T, to another T, into main line out to eng., pressure sender is mounted directly after the T where the two pumps come together. All this is in front of the wing spar near the floor in an RV6A. This would make the pumps in parallel & the pressure is the same from either pump, but both together pressure drops. David _____ From: "Mark Steitle" msteitle@gmail.com To: "Rotary motors in aircraft" Sent: Wednesday, June 13, 2012 8:36:19 AM Subject: [FlyRotary] Re: Fuel presure question. David, How are your pumps plumbed... in parallel or series? What kind of pressure do you get when running the backup pump only? Mark On 6/13/12, Tracy wrote: > Hmmmm... Mine goes up about a pound when I switch on the second pump. What > happens when you turn both off? > > Tracy > > Sent from my iPad > > On Jun 12, 2012, at 7:11 PM, hoursaway1@comcast.net wrote: > >> Question about fuel pressure indications, at fast idle 2200 RPM, fuel >> pressure is 42 PSI on EM2, if I switch on the back-up pump with the >> primary pump the pressure drops to 35 PSI, can here both pumps running, if >> I switch off either pump pressure goes back to 42 PSI. My system is 13B, >> stock red injectors all four, pressure regulator is stock Mazda on the end >> of fuel rail with vacume connection from dynamic chamber. Thanks, David >> R. Cook RV6A Rotary. > -- Homepage: http://www.flyrotary.com/ Archive and UnSub: http://mail.lancaironline.net:81/lists/flyrotary/List.html No virus found in this message. Checked by AVG - www.avg.com Version: 2012.0.2180 / Virus Database: 2433/5068 - Release Date: 06/13/12 ------=_NextPart_000_0037_01CD49B0.DCAD9E90 Content-Type: text/html; charset="US-ASCII" Content-Transfer-Encoding: quoted-printable

David,

 

If they don’t, each pump = should have its own circuit, otherwise you lose your = redundancy.

 

Bill B

 

From: = Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Mark Steitle
Sent: Wednesday, June 13, = 2012 8:24 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: = Two possible causes was : [FlyRotary] Re: Fuel presure = question.

 

David, 

 

Ed covered what I was thinking about a possible bad check-valve = in one of your pumps.  And a bunch of other stuff I hadn't = considered.

 

Mark 

On Wed, Jun 13, 2012 at 6:17 PM, Ed Anderson <eanderson@carolina.rr.com> wrote:

David, don't know whether you have considered this - = as you are aware the two pumps are able to work in parallel because the pumps = have check valves.  So if one pump is off and the other on, the on pump does = not pump fuel backwards through the off pump.  Since each pump produces the = 42 psi pressure by itself, one would assume the pumping elements in both pumps = are working properly.  Also assuming the pressure change is NOT due to = a malfunctioning pressure sensor.

 

Here are some things that you might want to = consider:

 

1.  That somehow when both pumps are on - one of = the pumps check valves is not closing properly.  Not a  pump = expert so not certain this could even happen - but the thought occurred to = me.

 

2.  The effect of Increased fuel flow rate due = to both pumps may be causing a pressure drop through an upstream = orifice (like perhaps your "T").

 

3.  Turning on both pumps (assuming on the same circuit) might cause sufficient voltage drop in the line sufficient to = decrease the pumping performance of both pumps - pump flow rates are sensitive to voltage variations.

 

4.  The pressure return regulator might be malfunctioning and opening due to the higher flow rate - easy to check, = just temporarily block off the return.  If the symptom disappears then = it’s the regulator.

 

 

Theoretically, if the fuel flow rate through the T's = and pumps  does not change with both pumps on, then the pressure should = remain the same  - which is what you are expecting, but not seeing.  =

 

So since the pressure does change (drops) - what = could cause this (assuming the pressure drop is real and not the result some strange malfunction of your gauge)?

 

  One thing that could cause it, is if the fuel = flow rate increases through an upstream orifice in your fuel line (say = at the "T" which feeds your two pumps)  then the pressure = on the other (downstream) side will drop.  Turn one of the pumps off, the = fuel flow rate drops, therefore there is less pressure drop across this = orifice  and your fuel pressure on the downstream side of the orifice will = again go up.

 

Its similar to a resistor in a circuit.  The = resistor value will remain static - the same, but if you pull more current = thought it, the voltage drop across it will increase resulting in less voltage on = the downstream side.  Reduce the current flow back to previous = rate and the voltage drop across the resistor decreases and therefore voltage on = the downstream side increase.

 

Another possible cause might be if both of your pumps = are fed off the same electrical line and there is sufficient resistance that = when both pumps are on the voltage drop causes less performance by both = pumps.

 

Just some WAGs that you might consider, if the suggestions make by others do not result in identifying the = cause.

 

Good Luck

 

Ed

 

Edward L. Anderson
Anderson Electronic Enterprises LLC
305 Reefton = Road
Weddington, = NC 28104
http://www.andersonee.com
http://www.eicommander.com=

 

Sent: Wednesday, June 13, 2012 6:43 PM

Subject: [FlyRotary] Re: Fuel presure question.

 

Fuel is gravity routed from = tanks to ganged fuel selector out to T-fitting with each pump on the sides of the T,  to another T,  into main line out to eng., = pressure sender is mounted directly after the T  where the two pumps come = together.   All this is in front of the wing spar near the floor in an RV6A. This = would make the pumps in parallel & the pressure is the same from either = pump, but both together pressure drops.   = David 

From: "Mark Steitle" msteitle@gmail.com
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Wednesday, June 13, = 2012 8:36:19 AM
Subject: [FlyRotary] Re: = Fuel presure question.

David,

How are your pumps plumbed... in parallel or series?  What kind = of
pressure do you get when running the backup pump only?

Mark

On 6/13/12, Tracy <rwstracy@gmail.com> wrote:
> Hmmmm...  Mine goes up about a pound when I switch on the = second pump.  What
> happens when you turn both off?
>
> Tracy
>
> Sent from my iPad
>
> On Jun 12, 2012, at 7:11 PM, hoursaway1@comcast.net wrote:
>
>> Question about fuel pressure indications, at fast idle 2200 = RPM, fuel
>> pressure is 42 PSI on EM2, if I switch on the back-up pump with = the
>> primary pump the pressure drops to 35 PSI, can here both pumps running, if
>> I switch off either pump pressure goes back to 42 PSI.  My = system is 13B,
>> stock red injectors all four, pressure regulator is stock Mazda = on the end
>> of fuel rail with vacume connection from dynamic chamber.  Thanks,  David
>> R. Cook  RV6A Rotary.
>

--
Homepage:  http://www.flyrotary.com/
Archive and UnSub:   http://mail.lancaironline.net:81/lists/flyrotary/List.h= tml

No virus found in this message.
Checked by AVG - www.avg.com
Version: 2012.0.2180 / Virus Database: 2433/5068 - Release Date: = 06/13/12

 

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