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Fuel Pressure Fixed

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Steve Glasgow

Joined: 10 Jan 2006
Posts: 674

Posted: Sat Jan 27, 2007 2:13 pm Post subject: Fuel Pressure Fixed

Turns out there was apparently air in the line to the sender.  Probably from 

lines being open on annual.



I flew before doing the procedure below and the fuel pressure was all over 

the place.  From 4 to 9.5 psi.



Anyway here is what to do to get the air out.  Disconnect wires from fuel 

sender.  Loosen sender so it can be moved by hand. Keep sender hand tight 

and turn on electric pump.  Now loosen sender till fuel comes out around the 

pipe fitting.  Then tighten to stop the fuel from leaking.  Turn off 

electric pump, secure sender and hook up wires.  Done.  From now on I will 

do this procedure whenever a fuel line is opened.



I flew before doing this and the fuel pressure was all over the place.  From 

4 to 9.5 psi.



Cappy

_________________
Steve Glasgow-Cappy
Cappy's Toy
RV-8 N123SG

sportav8r(at)gmail.com
Guest

Posted: Sat Jan 27, 2007 7:30 pm Post subject: Fuel Pressure Fixed

Interesting, Cappy.  I've never had to do this with either my oil or

fuel pressure transducers.  I figured fluid is fluid, whether oil,

gasoline or air; all should transfer the pressure to the sensor just

fine.  No problems thus far.  It's not like it could cavitate or

anything.



Makes one wonder... anyhow, glad it's fixed.   I might get to fly

tomorrow if the runway isn;t too mushy; the winds today were gusty on

the ground and 50 kts at 6000 AGL.  Turbulence in these-here

mountains!



-Stormy



On 1/27/07, Steve Glasgow <willfly(at)carolina.rr.com> wrote:

 	  Quote: 	
		   



 Turns out there was apparently air in the line to the sender.  Probably from

 lines being open on annual.



 I flew before doing the procedure below and the fuel pressure was all over

 the place.  From 4 to 9.5 psi.



 Anyway here is what to do to get the air out.  Disconnect wires from fuel

 sender.  Loosen sender so it can be moved by hand. Keep sender hand tight

 and turn on electric pump.  Now loosen sender till fuel comes out around the

 pipe fitting.  Then tighten to stop the fuel from leaking.  Turn off

 electric pump, secure sender and hook up wires.  Done.  From now on I will

 do this procedure whenever a fuel line is opened.



 I flew before doing this and the fuel pressure was all over the place.  From

 4 to 9.5 psi.



 Cappy

flyguy

Joined: 04 Mar 2006
Posts: 325

Posted: Sat Jan 27, 2007 7:46 pm Post subject: Fuel Pressure Fixed

looks like 20-30k in Ashe co. and snow

flurries...better keep it on the gnd. Stormer...RR

--- Bill Boyd <sportav8r(at)gmail.com> wrote:



 	  Quote: 	
		   

 <sportav8r(at)gmail.com>

 

 Interesting, Cappy.  I've never had to do this with

 either my oil or

 fuel pressure transducers.  I figured fluid is

 fluid, whether oil,

 gasoline or air; all should transfer the pressure to

 the sensor just

 fine.  No problems thus far.  It's not like it could

 cavitate or

 anything.

 

 Makes one wonder... anyhow, glad it's fixed.   I

 might get to fly

 tomorrow if the runway isn;t too mushy; the winds

 today were gusty on

 the ground and 50 kts at 6000 AGL.  Turbulence in

 these-here

 mountains!

 

 -Stormy

 

 On 1/27/07, Steve Glasgow <willfly(at)carolina.rr.com>

 wrote:

 > 

 Glasgow" <willfly(at)carolina.rr.com>

 >

 > Turns out there was apparently air in the line to

 the sender.  Probably from

 > lines being open on annual.

 >

 > I flew before doing the procedure below and the

 fuel pressure was all over

 > the place.  From 4 to 9.5 psi.

 >

 > Anyway here is what to do to get the air out. 

 Disconnect wires from fuel

 > sender.  Loosen sender so it can be moved by hand.

 Keep sender hand tight

 > and turn on electric pump.  Now loosen sender till

 fuel comes out around the

 > pipe fitting.  Then tighten to stop the fuel from

 leaking.  Turn off

 > electric pump, secure sender and hook up wires. 

 Done.  From now on I will

 > do this procedure whenever a fuel line is opened.

 >

 > I flew before doing this and the fuel pressure was

 all over the place.  From

 > 4 to 9.5 psi.

 >

 > Cappy

 >

 >

 >

 >

 >

 >

 



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Larry Bowen

Joined: 09 Jan 2006
Posts: 802
Location: NC, USA

Posted: Sat Jan 27, 2007 8:43 pm Post subject: Fuel Pressure Fixed

Glad to hear you are back in the air.



I filled up today at RUQ for the first time since leaving BKV in FL last

Sunday.  Only 26 gallons to fill up.  That's almost 19 mpg.  Better than the

Tundra.  Amazing to me.



I went to MTV for a late lunch afterwards.  There was a couple RV's there

getting ready to go as I can in.  From EXX, ROA, and GSO (?).   They're

everywhere.  



Keep building,



-

Larry Bowen, RV-8 & 7 emp.

Larry(at)BowenAero.com

http://BowenAero.com

 



[quote] --

_________________
Larry Bowen
RV-8 SOLD,
RV-7QB in progress...

Ron Schreck

Joined: 10 Jan 2006
Posts: 94
Location: Gold Hill, NC

Posted: Sun Jan 28, 2007 4:20 am Post subject: Fuel Pressure Fixed

Steve,



Glad to hear you are back in the air.  Actually, your problem and

solution makes perfect sense to me (Monday morning quarterbacking,

however).  If your fuel and oil pressure sensors are mounted high on the

firewall, it only makes sense that any air trapped in the lines will

never bleed out (down hill) without some help.  True, the trapped air

may transfer some measure of pressure, but being much more compressible

than a liquid it would certainly be a false reading.  I think your

solution merits a mention on the RV list and perhaps a suggestion that

these sensors be mounted low on the firewall to avoid the problem

altogether.  Nice work, Cappy!



Smokey



--

Steve Glasgow

Joined: 10 Jan 2006
Posts: 674

Posted: Sun Jan 28, 2007 4:29 am Post subject: Fuel Pressure Fixed

Thanks for the Kudos Smokey!  As you know I have been dealing with Low  or High fuel pressure since the beginning so I'm whiting till the jury is  in.  I have ordered a direct reading pressure gauge that should be  here Wednesday.  Then I can find out what the "real fuel pressure"  is.   

  

 Cappy

 [quote]   ---

_________________
Steve Glasgow-Cappy
Cappy's Toy
RV-8 N123SG

sportav8r(at)gmail.com
Guest

Posted: Sun Jan 28, 2007 5:06 am Post subject: Fuel Pressure Fixed

Smokey,



I think the trapped air compresses until it reaches equilib. and then

transmits all the pressure on down the line... in doing so it will

tend to dampen any pulses (soften the water-hammer effect,

what-have-you) but I think all the pressure will show up at the

transducer.  Enlighten me if I'm overlooking the obvious.



It sounds like Cappy might have fixed his gauge but broken some law of

physics.  Typical Cappy maneuver if you ask me.  Today I shall have to

see if he messed up Bernouli and Newton's, by seeing if my wing still

generates enough lift to fly 



Cappy, I'd appreciate it if you wouldn't break or damage physical laws

that the rest of us use every day, just to get your gauges reading

correctly; that's very selfish and won't be tolerated.



-Stormy



On 1/28/07, Ron Schreck <ronschreck(at)alltel.net> wrote:

[quote] 



 Steve,



 Glad to hear you are back in the air.  Actually, your problem and

 solution makes perfect sense to me (Monday morning quarterbacking,

 however).  If your fuel and oil pressure sensors are mounted high on the

 firewall, it only makes sense that any air trapped in the lines will

 never bleed out (down hill) without some help.  True, the trapped air

 may transfer some measure of pressure, but being much more compressible

 than a liquid it would certainly be a false reading.  I think your

 solution merits a mention on the RV list and perhaps a suggestion that

 these sensors be mounted low on the firewall to avoid the problem

 altogether.  Nice work, Cappy!



 Smokey



 --

Steve Glasgow

Joined: 10 Jan 2006
Posts: 674

Posted: Sun Jan 28, 2007 5:28 am Post subject: Fuel Pressure Fixed

What about compressibility of a gas verses a liquid.  Water pipes have  air trapped in them all the time to prevent hammer effect.  The pressure  sender is up the line not down the line.  Pressure is correct at the  engine, just not the pressure sender which is way above the  carburetor.    You may be correct if the sender is plumbed at the  carburetor but mine isn't.    All I know is it worked.  No more  oscillating fuel pressure.

  

 Stormy, are you giving us bad coordinates again?

  

 Love Cappy

 [quote]   ---

_________________
Steve Glasgow-Cappy
Cappy's Toy
RV-8 N123SG

sportav8r(at)gmail.com
Guest

Posted: Sun Jan 28, 2007 5:44 am Post subject: Fuel Pressure Fixed

Yeah, I've been known to lose my position fix on the internet before...



I'm wrestling with this and want to understand it.  You raise one

(calibration) point below: the pressure you read will be less than

carb pressure by the height of the fluid column betwee the carb and

the transducer.  Not sure how many inches of gasoline column equal one

p.s.i., but it varies with gasoline versus air because of the

differing densities.  Same reason a barometer made with mercury is

only a few feet tall versus one with water at around 32 feet tall!



The way I look at it, the pressure at my air tool is at the same value

as at the compressor regulator (until I squeeze the trigger and air

flow in the line causes a "voltage drop" - I'm talking about static

pressure, such as we read in a fuel pressure line that dead-ends into

a transducer).  To me this demonstrates that air sends its pressure

down the hose just like any other fluid, otherwise my pneumatic tools

would not work.



I still believe that when your fuel system pressurizes, everything in

the system, even trapped air, comes up to the same pressure and should

read as such on any transducer.  If I'm mistaken, let me know;

meanwhile my air tools still work just dandy on this exact principle.

But as you say, I've been wrong before.



I only belabor the point b/c I'm not convinced that this could have

fixed the problem and you might need to keep investigating.



-Stormy



On 1/28/07, Steve Glasgow <willfly(at)carolina.rr.com> wrote:

[quote]



 What about compressibility of a gas verses a liquid.  Water pipes have air

 trapped in them all the time to prevent hammer effect.  The pressure sender

 is up the line not down the line.  Pressure is correct at the engine, just

 not the pressure sender which is way above the carburetor.    You may be

 correct if the sender is plumbed at the carburetor but mine isn't.    All I

 know is it worked.  No more oscillating fuel pressure.



 Stormy, are you giving us bad coordinates again?



 Love Cappy



 ---

jclarkmail(at)gmail.com
Guest

Posted: Sun Jan 28, 2007 5:58 am Post subject: Fuel Pressure Fixed

Consider this:  Removing the "air" may have been the mechanism that removed some other "trapped particle" that might have been affecting the transducer.



James

 On 1/28/07, Bill Boyd <sportav8r(at)gmail.com (sportav8r(at)gmail.com)> wrote:[quote] --> RVSouthEast-List message posted by: "Bill Boyd" <sportav8r(at)gmail.com (sportav8r(at)gmail.com)>



Yeah, I've been known to lose my position fix on the internet before...



 I'm wrestling with this and want to understand it.  You raise one

(calibration) point below: the pressure you read will be less than

carb pressure by the height of the fluid column betwee the carb and

the transducer.  Not sure how many inches of gasoline column equal one 

p.s.i., but it varies with gasoline versus air because of the

differing densities.  Same reason a barometer made with mercury is

only a few feet tall versus one with water at around 32 feet tall!



The way I look at it, the pressure at my air tool is at the same value 

as at the compressor regulator (until I squeeze the trigger and air

flow in the line causes a "voltage drop" - I'm talking about static

pressure, such as we read in a fuel pressure line that dead-ends into 

a transducer).  To me this demonstrates that air sends its pressure

down the hose just like any other fluid, otherwise my pneumatic tools

would not work.



I still believe that when your fuel system pressurizes, everything in 

the system, even trapped air, comes up to the same pressure and should

read as such on any transducer.  If I'm mistaken, let me know;

meanwhile my air tools still work just dandy on this exact principle.

 But as you say, I've been wrong before.



I only belabor the point b/c I'm not convinced that this could have

fixed the problem and you might need to keep investigating.



-Stormy



On 1/28/07, Steve Glasgow < willfly(at)carolina.rr.com (willfly(at)carolina.rr.com)> wrote:

[quote]



 What about compressibility of a gas verses a liquid.  Water pipes have air

 trapped in them all the time to prevent hammer effect.  The pressure sender 

 is up the line not down the line.  Pressure is correct at the engine, just

 not the pressure sender which is way above the carburetor.    You may be

 correct if the sender is plumbed at the carburetor but mine isn't.    All I 

 know is it worked.  No more oscillating fuel pressure.



 Stormy, are you giving us bad coordinates again?



 Love Cappy



 ---

sportav8r(at)gmail.com
Guest

Posted: Sun Jan 28, 2007 6:31 am Post subject: Fuel Pressure Fixed

One never knows.



Seems these transducers do have a troubled service history, though.

Swaping them out usually fixes whatever problem one is posting to the

list about   Steve's direct reading gauge will tell all when he

gets it hooked in.



-B



On 1/28/07, James Clark <jclarkmail(at)gmail.com> wrote:

[quote] Consider this:  Removing the "air" may have been the mechanism that removed

 some other "trapped particle" that might have been affecting the transducer.



 James



  On 1/28/07, Bill Boyd <sportav8r(at)gmail.com> wrote:

 > 

 >

 > Yeah, I've been known to lose my position fix on the internet before...

 >

 > I'm wrestling with this and want to understand it.  You raise one

 > (calibration) point below: the pressure you read will be less than

 > carb pressure by the height of the fluid column betwee the carb and

 > the transducer.  Not sure how many inches of gasoline column equal one

 > p.s.i., but it varies with gasoline versus air because of the

 > differing densities.  Same reason a barometer made with mercury is

 > only a few feet tall versus one with water at around 32 feet tall!

 >

 > The way I look at it, the pressure at my air tool is at the same value

 > as at the compressor regulator (until I squeeze the trigger and air

 > flow in the line causes a "voltage drop" - I'm talking about static

 > pressure, such as we read in a fuel pressure line that dead-ends into

 > a transducer).  To me this demonstrates that air sends its pressure

 > down the hose just like any other fluid, otherwise my pneumatic tools

 > would not work.

 >

 > I still believe that when your fuel system pressurizes, everything in

 > the system, even trapped air, comes up to the same pressure and should

 > read as such on any transducer.  If I'm mistaken, let me know;

 > meanwhile my air tools still work just dandy on this exact principle.

 > But as you say, I've been wrong before.

 >

 > I only belabor the point b/c I'm not convinced that this could have

 > fixed the problem and you might need to keep investigating.

 >

 > -Stormy

 >

 > On 1/28/07, Steve Glasgow < willfly(at)carolina.rr.com> wrote:

 > >

 > >

 > > What about compressibility of a gas verses a liquid.  Water pipes have

 air

 > > trapped in them all the time to prevent hammer effect.  The pressure

 sender

 > > is up the line not down the line.  Pressure is correct at the engine,

 just

 > > not the pressure sender which is way above the carburetor.    You may be

 > > correct if the sender is plumbed at the carburetor but mine isn't.

 All I

 > > know is it worked.  No more oscillating fuel pressure.

 > >

 > > Stormy, are you giving us bad coordinates again?

 > >

 > > Love Cappy

 > >

 > > ---

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