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Findings on the AFP purge valve

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mstewart(at)iss.net
Guest

Posted: Wed Oct 04, 2006 3:59 am Post subject: Findings on the AFP purge valve

I received an excellent report from Don at AFP on the purge valve.  

From his report, “.  Upon inspection of the valve assembly it was apparent that the stop screw had not been lock wired and had started to back out allowing the bottom O-ring to unseat from the lower boss in the housing, thus allowing fuel to bypass to the return port.”  

Here is a nice picture of it.  

http://www.mstewart.net/deletesoon/purgevalve.jpg  

   

He went on to say “This is a disturbing finding as there are multiple warnings and pictures in the installation manual as well as a tag on the stop screw instructing the installer to lockwire the screw after installation.” While I don’t remember the tag on the device, im sure the manual mentions it. Tag or no tag, manual or no manual, it should have been caught.  Im fortunate to live at a big field with lots of experience.  I have had quite a few folks look over the plane prior to its first flight. It was missed by 2 IA’s,  3 A&P’s. 1 DAR (would not expect him to catch this), god knows how many others folks who have poured over my super 8 installation, and finally me.   

   

So in the end 2 purge valve system failures, both builder errors. Great!  

   

These aren’t the only issues I’ve had on my planes over the years that could have been prevented, they wont be the last. But I have concluded that this purge valve setup adds complexity and failure modes to a system that is unjustified. Anything in the fuel delivery system should be there for a good reason. In my years and couple thousand hours of flying behind the AFP system in multiple RV’s,  I cant once say I’ve needed the purge valve.  Its not going back in my plane. As for the rest of the AFP system, I think its great and Ive never heard of or experienced any problems with it with the exception of the electric fuel pump failures which have been discussed before and are in the archives for your reading pleasure.  

   

So my 2 cents on the AFP fuel injection system    Worth every penny  
Leave out the purge      valve  
Increase      the life of your electric boost pump by replacing the stock filter element      with a 25 micron one available from Flow EZ part number 8504-05.     

   

Flame suit donned.  

Best,  

Mike  

   

   

   

   

   

      [quote][b]

phil(at)petrasoft.net
Guest

Posted: Wed Oct 04, 2006 5:43 am Post subject: Findings on the AFP purge valve

Michael,



Thanks for the report. Most people would have just swept that one under 

the rug. It's refreshing to see something like this debated with just 

cold hard facts and little if any ego. Everyone now has another piece of 

GOOD information to use in their decision making process. Thanks again, 

the life you save could be my own. Now off to the hangar to make sure I 

have a certain little piece of stainless wire.....

Godspeed,



Phil Birkelbach - Houston Texas

RV-7 N727WB

http://www.myrv7.com

Do Not Archive



Stewart, Michael (ISS Atlanta) wrote:

 	  Quote: 	
		  

 I received an excellent report from Don at AFP on the purge valve.



 From his report, “. Upon inspection of the valve assembly it was 

 apparent that the stop screw had not been lock wired and had started 

 to back out allowing the bottom O-ring to unseat from the lower boss 

 in the housing, thus allowing fuel to bypass to the return port.”



 Here is a nice picture of it.



 http://www.mstewart.net/deletesoon/purgevalve.jpg



 He went on to say “This is a disturbing finding as there are multiple 

 warnings and pictures in the installation manual as well as a tag on 

 the stop screw instructing the installer to lockwire the screw after 

 installation.” While I don’t remember the tag on the device, im sure 

 the manual mentions it. Tag or no tag, manual or no manual, it should 

 have been caught. Im fortunate to live at a big field with lots of 

 experience. I have had quite a few folks look over the plane prior to 

 its first flight. It was missed by 2 IA’s, 3 A&P’s. 1 DAR (would not 

 expect him to catch this), god knows how many others folks who have 

 poured over my super 8 installation, and finally me.



 So in the end 2 purge valve system failures, both builder errors. Great!



 These aren’t the only issues I’ve had on my planes over the years that 

 could have been prevented, they wont be the last. But I have concluded 

 that this purge valve setup adds complexity and failure modes to a 

 system that is unjustified. Anything in the fuel delivery system 

 should be there for a good reason. In my years and couple thousand 

 hours of flying behind the AFP system in multiple RV’s, I cant once 

 say I’ve needed the purge valve. Its not going back in my plane. As 

 for the rest of the AFP system, I think its great and Ive never heard 

 of or experienced any problems with it with the exception of the 

 electric fuel pump failures which have been discussed before and are 

 in the archives for your reading pleasure.



 So my 2 cents on the AFP fuel injection system



    1. Worth every penny

    2. Leave out the purge valve**

    3. Increase the life of your electric boost pump by replacing the

       stock filter element with a 25 micron one available from Flow EZ

       part number 8504-05.



 Flame suit donned.



 Best,



 Mike



 *

 *

recapen(at)earthlink.net
Guest

Posted: Wed Oct 04, 2006 6:16 am Post subject: Findings on the AFP purge valve

<<SNIP>>



 	  Quote: 	
		  From: Phil Birkelbach <phil(at)petrasoft.net>

Now off to the hangar to make sure I 

have a certain little piece of stainless wire.....


	


Ditto for me......same thanks - same wire.......

rv8a2001(at)yahoo.com
Guest

Posted: Wed Oct 04, 2006 6:52 am Post subject: Findings on the AFP purge valve

Wow, now I am second guessing if I have the screw tied up.......will check this weekend. Thanks for figuring it out.

 

 

Scott Bilinski

RV-8a 

  

   ---

dan(at)rvproject.com
Guest

Posted: Wed Oct 04, 2006 6:56 am Post subject: Findings on the AFP purge valve

Since the AFP servo still flows fuel even when the  mixture is pulled to idle/cutoff, the purge valve is a SAFE choice imho.   Just visualize fuel having pooled in your sump (or airbox), and then you go to  start the engine.

  

 This is not a "how easy is it to start"  issue.  It's a safety issue imho.

  

 Consider keeping the purge valve.

  

 )_( Dan

 RV-7 N714D (1085 hours)

 www.rvproject.com / www.weathermeister.com

 [quote]   ---

mstewart(at)iss.net
Guest

Posted: Wed Oct 04, 2006 7:32 am Post subject: Findings on the AFP purge valve

Yes I have considered this.  

Going to idle cut off, the engine can have a tendency to try and keep running a little. I have compensated for this by going to idle cut off, waiting for the fan to nearly stop, and killing the ignitions. This has worked fine over time. I do not think there is any chance of fuel pooling in the sump or airbox. I certainly have not experienced that.   

Mike  

Do not archive  

   

   

   

         

  

From: owner-rv-list-server(at)matronics.com [mailto:owner-rv-list-server(at)matronics.com] On Behalf Of Dan Checkoway

 Sent: Wednesday, October 04, 2006 10:56 AM

 To: rv-list(at)matronics.com

 Subject: Re: Findings on the AFP purge valve  

  

     

Since the AFP servo still flows fuel even when the mixture is pulled to idle/cutoff, the purge valve is a SAFE choice imho.  Just visualize fuel having pooled in your sump (or airbox), and then you go to start the engine.  

    

   

    

This is not a "how easy is it to start" issue.  It's a safety issue imho.  

    

   

    

Consider keeping the purge valve.  

    

   

    

)_( Dan  

    

RV-7 N714D (1085 hours)  

    

www.rvproject.com / www.weathermeister.com  

  [quote]    

---

Terry Watson

Joined: 09 Jan 2006
Posts: 290
Location: Seattle, WA USA

Posted: Wed Oct 04, 2006 8:18 am Post subject: Findings on the AFP purge valve

Yes Michael, me too. Classy move.



Terry

Do not archive




Michael,



Thanks for the report. Most people would have just swept that one under 

the rug. It's refreshing to see something like this debated with just 

cold hard facts and little if any ego. Everyone now has another piece of 

GOOD information to use in their decision making process. Thanks again, 

the life you save could be my own. Now off to the hangar to make sure I 

have a certain little piece of stainless wire.....

Godspeed,



Phil Birkelbach - Houston Texas

RV-7 N727WB

http://www.myrv7.com

pitts_pilot(at)bellsouth.
Guest

Posted: Wed Oct 04, 2006 12:28 pm Post subject: Findings on the AFP purge valve

Stewart, Michael (ISS Atlanta) wrote:

  	  Quote: 	
		                  v\:* {behavior:url(#default#VML);} o\:* {behavior:url(#default#VML);} w\:* {behavior:url(#default#VML);} .shape {behavior:url(#default#VML);}  <![endif]-->            <![endif]-->       <![endif]-->            

Yes I have considered this.      

Going to idle cut off, the engine can have a tendency to try and keep running a little. I have compensated for this by going to idle cut off, waiting for the fan to nearly stop, and killing the ignitions. This has worked fine over time. I do not think there is any chance of fuel pooling in the sump or airbox. I certainly have not experienced that.       

Mike      

Do not archive   

 	
 The only downside to this procedure is that there is 'extra' fuel in the cylinders which will wash the oil off the cylinder walls.  Since Michael flies a whole lot, probably not a problem, but for an engine that's seldom run it'll mean that the steel cylinders will rust a little faster.  Given Michaels experience with the valve ...... I'd probably do the same.  Too bad AFP won't fix the idle cutoff problem in the controller instead of adding the purge valve.

 Linn

     [quote][b]

Mark Phillips in TN

Joined: 10 Jan 2006
Posts: 431
Location: Columbia, TN

Posted: Wed Oct 04, 2006 1:44 pm Post subject: Findings on the AFP purge valve

In a message dated 10/04/2006 3:32:00 PM Central Daylight Time, pitts_pilot(at)bellsouth.net writes:

  	  Quote: 	
		  The only downside to this procedure is that there is 'extra' fuel in the cylinders which will wash the oil off the cylinder walls 	


 >>>

  

 How about shutting off fuel pump & valve on taxi to hangar?

  

 Mark do not archive

  [quote][b]

_________________
From The PossumWorks...

rocketbob(at)gmail.com
Guest

Posted: Wed Oct 04, 2006 2:13 pm Post subject: Findings on the AFP purge valve

Fuel will only wash on the cylinder with an open intake valve when the engine is shut down, and even so it probably vaporizes quickly.  And any oil in the cylinder will likely trickle down over the spot where the fuel was.  I would also bet that the fuel vaporizes before it has a chance to dribble past the intake valve. 



Regards,

Bob Japundza

RV-6 flying F1 under const.



On 10/4/06, linn Walters <pitts_pilot(at)bellsouth.net  (pitts_pilot(at)bellsouth.net)> wrote:[quote]          The only downside to this procedure is that there is 'extra' fuel in the cylinders which will wash the oil off the cylinder walls.  Since Michael flies a whole lot, probably not a problem, but for an engine that's seldom run it'll mean that the steel cylinders will rust a little faster.  Given Michaels experience with the valve ...... I'd probably do the same.  Too bad AFP won't fix the idle cutoff problem in the controller instead of adding the purge valve.

 Linn

      	  Quote: 	
		  



	


[b]

pitts_pilot(at)bellsouth.
Guest

Posted: Wed Oct 04, 2006 6:58 pm Post subject: Findings on the AFP purge valve

AFAIK, the oil washing away (what little is left in the combustion chamber at shutdown) was the reason why our engines have an idle cutoff position instead of just turning the mags off.  But, what do I know anyway???

 Linn

 

 do not archive

 Bob J. wrote:

 [quote]Fuel will only wash on the cylinder with an open intake valve when the engine is shut down, and even so it probably vaporizes quickly.  And any oil in the cylinder will likely trickle down over the spot where the fuel was.  I would also bet that the fuel vaporizes before it has a chance to dribble past the intake valve. 

   

 Regards,

 Bob Japundza

 RV-6 flying F1 under const.

   

   On 10/4/06, linn Walters <pitts_pilot(at)bellsouth.net     (pitts_pilot(at)bellsouth.net)> wrote:    	  Quote: 	
		                  The only downside to this procedure is that there is 'extra' fuel in the cylinders which will wash the oil off the cylinder walls.  Since Michael flies a whole lot, probably not a problem, but for an engine that's seldom run it'll mean that the steel cylinders will rust a little faster.  Given Michaels experience with the valve ...... I'd probably do the same.  Too bad AFP won't fix the idle cutoff problem in the controller instead of adding the purge valve.

      Linn

            	  Quote: 	
		  



	
     

   

	
 [b]

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