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mstewart(at)iss.net
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 Posted: Mon Oct 02, 2006 4:31 am Post subject: I've sworn off purge valve installations |
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After my second failure in a couple thousand hours of running fuel injection with pruge valves, I have concluded they are unnecessary and can have multiple failure modes that can bring you down.
As many of you know Airflow Performance of Spartanburg SC sells a terrific fuel injection system for all kinds of engines. from boats, to dragsters, to planes. I have had their system on 2 RV’s and have had 2 failures in the purge system. The purpose in the purge valve is simple. On a hot start, pull the valve, turn your pump on, and allow the hot vapors out for a few seconds. Close the valve and start your normal hot start procedures.
On my RV-6 I had the purge vale return line running into the cockpit and into a tee on the fuel inlet near the tank selector switch. AFP recommends this returning back to the tank, but I felt this to be too complex an installation. One day, while scudding back from SnF, close to home base, with Michelle in the right seat, the engine coughed and would barely run. I managed to limp home. After weeks of troubleshooting, it turned out that I had a crack in a tube FWF on the purge return line. This crack was allowing air into the return line, and hence air into the fuel flow to the engine. After this incident I decided on my next plane, I would NOT put the purge return line into the fuel supply system. This failure could have put me and my wife in the trees.
On my 8, I ran the purge return into the left tank vent. Thought being, let the vapors and a little fuel run to the ground. Don’t let a line leak here spoil my fuel. So on a trip last week with several RV’s and wifes to NYC for a play and a movie, plane died on landing rollout in NJ. ARGH! We finished our weekend getaway with the wife’s, but on Sunday I put wife on a Delta flight home and began troubleshooting. What I found was the plane was way lean in running and would barely idle below 1500. I removed the fuel inlet to the servo and there was plenty of fuel going in, but the engine was not getting it. I checked screens and a few other things and no joy. I decided it was the servo not metering the fuel properly. I finally decided I try taking off and climbing to altitude and see if mother nature would richen it with altitude. Sure enough, around 7k’ I would get egt’s at peak, and at 10k’ I could run a little ROP. BUT the fuel flow was +4gph more than normal. How could that be? I dunno, but it was running smooth and I flew her home to Atlanta.
Safe in my own hanger, I removed the servo and flow divider and sent it to AFP. Don returned it with no problem found. ARGH! Spent the weekend troubleshooting and found the problem. The Purge valve was leaking internally and some fuel was by passing and going to the return side. Actually a lot of fuel was going to the return. This was causing lean operation and high fuel flow. I have now sent this to AFP for repair. I also suspect that this valve has been sending fuel to the return all along in the past 300 hours. I have gotten from day 1, and unexplained +1.5gph with my boost pump on.
In a couple thousand hours of RV injected operation in multiple aircraft, I have not found I needed this purge valve function for hot starts. In fact all I really use it for is to shut down the engine. Hot starts are easily handled with proper technique. I have now sworn off this purge valve madness as it provides no value in an RV and multiple failure modes.
Thought some of you might find this information useful.
Best,
Mike Stewart
[quote][b]
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RVer273sb(at)aol.com
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| Posted: Mon Oct 02, 2006 5:13 am Post subject: I've sworn off purge valve installations |
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I have 1400 hours running a purge valve
set up with no problems....
Stew RV-4
Do not archive
[quote][b]
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chaztuna(at)adelphia.net
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| Posted: Mon Oct 02, 2006 8:07 am Post subject: I've sworn off purge valve installations |
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Mike
Thanks for your report. Could you tell me what type of aluminum tubing you had used on your previous RV? Was it the 3003 Versitube which Vans supplies? Or something else. Do you have any theory on why that fuel line cracked?
Charlie Kuss
[quote]After my second failure in a couple thousand hours of running fuel injection with pruge valves, I have concluded they are unnecessary and can have multiple failure modes that can bring you down.
As many of you know Airflow Performance of Spartanburg SC sells a terrific fuel injection system for all kinds of engines. from boats, to dragsters, to planes. I have had their system on 2 RV’s and have had 2 failures in the purge system. The purpose in the purge valve is simple. On a hot start, pull the valve, turn your pump on, and allow the hot vapors out for a few seconds. Close the valve and start your normal hot start procedures.
On my RV-6 I had the purge vale return line running into the cockpit and into a tee on the fuel inlet near the tank selector switch. AFP recommends this returning back to the tank, but I felt this to be too complex an installation. One day, while scudding back from SnF, close to home base, with Michelle in the right seat, the engine coughed and would barely run. I managed to limp home. After weeks of troubleshooting, it turned out that I had a crack in a tube FWF on the purge return line. This crack was allowing air into the return line, and hence air into the fuel flow to the engine. After this incident I decided on my next plane, I would NOT put the purge return line into the fuel supply system. This failure could have put me and my wife in the trees.
On my 8, I ran the purge return into the left tank vent. Thought being, let the vapors and a little fuel run to the ground. Don’t let a line leak here spoil my fuel. So on a trip last week with several RV’s and wifes to NYC for a play and a movie, plane died on landing rollout in NJ. ARGH! We finished our weekend getaway with the wife’s, but on Sunday I put wife on a Delta flight home and began troubleshooting. What I found was the plane was way lean in running and would barely idle below 1500. I removed the fuel inlet to the servo and there was plenty of fuel going in, but the engine was not getting it. I checked screens and a few other things and no joy. I decided it was the servo not metering the fuel properly. I finally decided I try taking off and climbing to altitude and see if mother nature would richen it with altitude. Sure enough, around 7k’ I would get egt’s at peak, and at 10k’ I could run a little ROP. BUT the fuel flow was +4gph more than normal. How could that be? I dunno, but it was running smooth and I flew her home to Atlanta.
Safe in my own hanger, I removed the servo and flow divider and sent it to AFP. Don returned it with no problem found. ARGH! Spent the weekend troubleshooting and found the problem. The Purge valve was leaking internally and some fuel was by passing and going to the return side. Actually a lot of fuel was going to the return. This was causing lean operation and high fuel flow. I have now sent this to AFP for repair. I also suspect that this valve has been sending fuel to the return all along in the past 300 hours. I have gotten from day 1, and unexplained +1.5gph with my boost pump on.
In a couple thousand hours of RV injected operation in multiple aircraft, I have not found I needed this purge valve function for hot starts. In fact all I really use it for is to shut down the engine. Hot starts are easily handled with proper technique. I have now sworn off this purge valve madness as it provides no value in an RV and multiple failure modes.
Thought some of you might find this information useful.
Best,
Mike Stewart
[b]
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mstewart(at)iss.net
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| Posted: Mon Oct 02, 2006 9:10 am Post subject: I've sworn off purge valve installations |
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It would have been. But late in the build cycle, I met and became best friends with a Delta mechanic who came into my project late and nearing the first flight. He said “I aint letting you up there with that el cheapo “Oh” tube as he called it. He proceeded to rip out every soft aluminum tube I had and replaced it with stainless steel. Every piece! Dozens of them! He was a master with this stuff and could take a couple measurements with a steel ruler, and come back with a perfectly fitted SS aircraft tube ready to go. Years in the hydraulics shop at the Delta hub here in Atlanta and I guess you get pretty good with this stuff. So I originally had in this picture here soft 3003, but it was replaced with stainless steel. I pointed the arrow to where the crack was. Right behind the b-nut sleeve. Again the pic, from a vintage late 90’s digital camera that only geeks were using at the time, is of soft tube but it was SS that cracked ~800 hours as I recall.
http://www.mstewart.net/deletesoon/engtopcrack.jpg
My theory was that flex line should absolutely have been installed here. That spider was no doubt bobbing around hung out there so far, while the rear baffle was not moving much at all I suspect.
Mike
From: owner-rv-list-server(at)matronics.com [mailto:owner-rv-list-server(at)matronics.com] On Behalf Of Charlie Kuss
Sent: Monday, October 02, 2006 11:49 AM
To: rv-list(at)matronics.com
Subject: Re: I've sworn off purge valve installations
Mike
Thanks for your report. Could you tell me what type of aluminum tubing you had used on your previous RV? Was it the 3003 Versitube which Vans supplies? Or something else. Do you have any theory on why that fuel line cracked?
Charlie Kuss
After my second failure in a couple thousand hours of running fuel injection with pruge valves, I have concluded they are unnecessary and can have multiple failure modes that can bring you down.
As many of you know Airflow Performance of Spartanburg SC sells a terrific fuel injection system for all kinds of engines. from boats, to dragsters, to planes. I have had their system on 2 RV’s and have had 2 failures in the purge system. The purpose in the purge valve is simple. On a hot start, pull the valve, turn your pump on, and allow the hot vapors out for a few seconds. Close the valve and start your normal hot start procedures.
On my RV-6 I had the purge vale return line running into the cockpit and into a tee on the fuel inlet near the tank selector switch. AFP recommends this returning back to the tank, but I felt this to be too complex an installation. One day, while scudding back from SnF, close to home base, with Michelle in the right seat, the engine coughed and would barely run. I managed to limp home. After weeks of troubleshooting, it turned out that I had a crack in a tube FWF on the purge return line. This crack was allowing air into the return line, and hence air into the fuel flow to the engine. After this incident I decided on my next plane, I would NOT put the purge return line into the fuel supply system. This failure could have put me and my wife in the trees.
On my 8, I ran the purge return into the left tank vent. Thought being, let the vapors and a little fuel run to the ground. Don’t let a line leak here spoil my fuel. So on a trip last week with several RV’s and wifes to NYC for a play and a movie, plane died on landing rollout in NJ. ARGH! We finished our weekend getaway with the wife’s, but on Sunday I put wife on a Delta flight home and began troubleshooting. What I found was the plane was way lean in running and would barely idle below 1500. I removed the fuel inlet to the servo and there was plenty of fuel going in, but the engine was not getting it. I checked screens and a few other things and no joy. I decided it was the servo not metering the fuel properly. I finally decided I try taking off and climbing to altitude and see if mother nature would richen it with altitude. Sure enough, around 7k’ I would get egt’s at peak, and at 10k’ I could run a little ROP. BUT the fuel flow was +4gph more than normal. How could that be? I dunno, but it was running smooth and I flew her home to Atlanta.
Safe in my own hanger, I removed the servo and flow divider and sent it to AFP. Don returned it with no problem found. ARGH! Spent the weekend troubleshooting and found the problem. The Purge valve was leaking internally and some fuel was by passing and going to the return side. Actually a lot of fuel was going to the return. This was causing lean operation and high fuel flow. I have now sent this to AFP for repair. I also suspect that this valve has been sending fuel to the return all along in the past 300 hours. I have gotten from day 1, and unexplained +1.5gph with my boost pump on.
In a couple thousand hours of RV injected operation in multiple aircraft, I have not found I needed this purge valve function for hot starts. In fact all I really use it for is to shut down the engine. Hot starts are easily handled with proper technique. I have now sworn off this purge valve madness as it provides no value in an RV and multiple failure modes.
Thought some of you might find this information useful.
Best,
Mike Stewart
01234567890123
[quote][b]
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sbuc(at)hiwaay.net
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| Posted: Mon Oct 02, 2006 10:38 am Post subject: I've sworn off purge valve installations |
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Stewart, Michael (ISS Atlanta) wrote:
| Quote: | It would have been. But late in the build cycle, I met and became best
friends with a Delta mechanic who came into my project late and nearing
the first flight. He said “I aint letting you up there with that el
cheapo “Oh” tube as he called it. He proceeded to rip out every soft
aluminum tube I had and replaced it with stainless steel. Every piece!
Dozens of them! He was a master with this stuff and could take a couple
measurements with a steel ruler, and come back with a perfectly fitted
SS aircraft tube ready to go. Years in the hydraulics shop at the Delta
hub here in Atlanta and I guess you get pretty good with this stuff. So
I originally had in this picture here soft 3003, but it was replaced
with stainless steel. I pointed the arrow to where the crack was. Right
behind the b-nut sleeve. Again the pic, from a vintage late 90’s digital
camera that only geeks were using at the time, is of soft tube but it
was SS that cracked ~800 hours as I recall.
|
Wonder if the softer, "cheap" aluminum line would have been less
susceptible than the stainless to cracking?
Sam Buchanan
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dan(at)rvproject.com
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| Posted: Mon Oct 02, 2006 11:20 am Post subject: I've sworn off purge valve installations |
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Baffles move/flex more than you might think. Personally, I'd only use HOSES
for critical fuel lines (especially the metered fuel supply!), and have the
hoses go uninterrupted, right through the baffles via a rubber
grommet...just my 2 cents!
do not archive
)_( Dan
RV-7 N714D (1082 hours w/purge valve & hoses)
www.rvproject.com / www.weathermeister.com
---
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Mark Phillips in TN
Joined: 10 Jan 2006
Posts: 431
Location: Columbia, TN
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| Posted: Mon Oct 02, 2006 1:56 pm Post subject: I've sworn off purge valve installations |
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Thanks for the writeup, Mike-
In deference to the KISS principle, how much hard evidence/experience is there to support installation of a purge valve in an RV as opposed to certified a/c where it may really be needed? Anyone tried starting their hot IOs without it or done any actual testing to determine if it is really a necessity, or something one "might" need once or twice a year under worst conditions? Thinking here is to reduce fuel lines/fittings in a REALLY bad spot to have a failure (and extra co$t) vs. a rare inconvenience which is not a safety-of-flight issue...
Mark do not archive
[quote][b]
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From The PossumWorks... |
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Terry Watson
Joined: 09 Jan 2006
Posts: 290
Location: Seattle, WA USA
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| Posted: Mon Oct 02, 2006 2:34 pm Post subject: I've sworn off purge valve installations |
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I would also be concerned about shutting down the engine. AP’s owner’s manual says that the mixture control will NOT reliably cut off fuel flow enough to stop the engine.
Terry
From: owner-rv-list-server(at)matronics.com [mailto:owner-rv-list-server(at)matronics.com] On Behalf Of Fiveonepw(at)aol.com
Sent: Monday, October 02, 2006 2:55 PM
To: rv-list(at)matronics.com
Subject: Re: I've sworn off purge valve installations
Thanks for the writeup, Mike-
In deference to the KISS principle, how much hard evidence/experience is there to support installation of a purge valve in an RV as opposed to certified a/c where it may really be needed? Anyone tried starting their hot IOs without it or done any actual testing to determine if it is really a necessity, or something one "might" need once or twice a year under worst conditions? Thinking here is to reduce fuel lines/fittings in a REALLY bad spot to have a failure (and extra co$t) vs. a rare inconvenience which is not a safety-of-flight issue...
Mark do not archive
01234567890123
[quote][b]
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av8er2fly(at)peoplepc.com
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| Posted: Mon Oct 02, 2006 3:10 pm Post subject: I've sworn off purge valve installations |
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What would your normal start be with out the purge valve? I do not have a purge valve but was considering putting one on because of real hard hot starts. Any Ideas would be appreciated. Mark Rose RV8A 137MR IO360 85 fun Hrs.
[quote] ---
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sarg314(at)comcast.net
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| Posted: Mon Oct 02, 2006 5:00 pm Post subject: I've sworn off purge valve installations |
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Stewart, Michael (ISS Atlanta) wrote:
| Quote: | After weeks of troubleshooting, it turned out that I had a crack in a
tube FWF on the purge return line. This crack was allowing air into
the return line, and hence air into the fuel flow to the engine. After
this incident I decided on my next plane, I
I thought there weren't supposed to be any solid tubes FWF. The
|
vibration makes them crack.
--
Tom Sargent, RV-6A
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pitts_pilot(at)bellsouth.
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| Posted: Mon Oct 02, 2006 6:03 pm Post subject: I've sworn off purge valve installations |
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av8er2fly(at)peoplepc.com (av8er2fly(at)peoplepc.com) wrote:
| Quote: | st1\:* { BEHAVIOR: url(#default#ieooui) } <![endif]--> What would your normal start be with out the purge valve? I do not have a purge valve but was considering putting one on because of real hard hot starts. Any Ideas would be appreciated. Mark Rose RV8A 137MR IO360 85 fun Hrs.
|
Well, it all depends on what's causing the hard starts when hot. This will take some sleuthing on your part. The problem may be that it takes some extra pump time to fully pressurize the system and get fuel through the injectors. The problem may not be vapor in the lines. When you have a hot start problem have someone look at the exhaust. If you see vapor (think the wavy view of the air down a hot road) and it doesn't start than it's too rich and when it does start then you'll see black smoke out the exhaust. If you don't see anything, keep hitting the boost pump ..... keeping track of how long the total pump run is ..... a second or two at a time until it starts ..... you'll need someone to watch that exhaust. If it still won't start, then it's time to pull some plugs to see if they're wet.
If you suspect vapor lock .... the only cure is positive pressure on the system. I'm partial to the 'serial flow system' .... where the boost pump feeds the engine pump which feeds the controller. Others like the 'parallel flow system' and that's OK too ...... but being able to pressurize the whole system is, to me, the key.
If you can mount your boost pump as low as possible in the cockpit ..... which shouldn't get as hot as the engne compartment ..... and keep it cool, positive head pressure is always available ..... unless you run the tank dry!!!
Bottom line, the sequence you use in starting can be very important and it's just a learning (leaning????  ) curve 'till you find what the engine really likes.
Good luck!!!
Linn
do not archive
[quote][b]
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Doug Gray
Joined: 10 Jan 2006
Posts: 112
Location: Sydney, Australia
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| Posted: Tue Oct 03, 2006 3:02 am Post subject: I've sworn off purge valve installations |
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I think the critical factor here is that the tube is unsupported. I
suspect a clamp or two would have significantly reduced vibration in the
tube and prevented the cracking.
What type of fuel valve failed.
Doug Gray
| Quote: |
On my RV-6 I had the purge vale return line running into the cockpit
and into a tee on the fuel inlet near the tank selector switch. AFP
recommends this returning back to the tank, but I felt this to be too
complex an installation. One day, while scudding back from SnF, close
to home base, with Michelle in the right seat, the engine coughed and
would barely run. I managed to limp home. After weeks of
troubleshooting, it turned out that I had a crack in a tube FWF on the
purge return line. This crack was allowing air into the return line,
and hence air into the fuel flow to the engine. After this incident I
decided on my next plane, I would NOT put the purge return line into
the fuel supply system. This failure could have put me and my wife in
the trees.
On my 8, I ran the purge return into the left tank vent. Thought
being, let the vapors and a little fuel run to the ground. Don’t let a
line leak here spoil my fuel. So on a trip last week with several RV’s
and wifes to NYC for a play and a movie, plane died on landing rollout
in NJ. ARGH! We finished our weekend getaway with the wife’s, but on
Sunday I put wife on a Delta flight home and began troubleshooting.
What I found was the plane was way lean in running and would barely
idle below 1500. I removed the fuel inlet to the servo and there was
plenty of fuel going in, but the engine was not getting it. I checked
screens and a few other things and no joy. I decided it was the servo
not metering the fuel properly. I finally decided I try taking off and
climbing to altitude and see if mother nature would richen it with
altitude. Sure enough, around 7k’ I would get egt’s at peak, and at
10k’ I could run a little ROP. BUT the fuel flow was +4gph more than
normal. How could that be? I dunno, but it was running smooth and I
flew her home to Atlanta.
Safe in my own hanger, I removed the servo and flow divider and sent
it to AFP. Don returned it with no problem found. ARGH! Spent the
weekend troubleshooting and found the problem. The Purge valve was
leaking internally and some fuel was by passing and going to the
return side. Actually a lot of fuel was going to the return. This was
causing lean operation and high fuel flow. I have now sent this to AFP
for repair. I also suspect that this valve has been sending fuel to
the return all along in the past 300 hours. I have gotten from day 1,
and unexplained +1.5gph with my boost pump on.
In a couple thousand hours of RV injected operation in multiple
aircraft, I have not found I needed this purge valve function for hot
starts. In fact all I really use it for is to shut down the engine.
Hot starts are easily handled with proper technique. I have now sworn
off this purge valve madness as it provides no value in an RV and
multiple failure modes.
Thought some of you might find this information useful.
Best,
Mike Stewart
|
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panamared3(at)brier.net
Guest
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| Posted: Tue Oct 03, 2006 4:02 am Post subject: I've sworn off purge valve installations |
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I have an IO -360 and hot starts are a problem for me. I have actually had
to take the cowl off to let the fuel lines cool down before I could fly
home. I even had Dan Rivera of Airflow Performance coach me, will little
improvement in hot starts.
Inconvenience, well I just did not fly from June through September before I
put in the purge valve. Slowly I have been trying various techniques and
systems to improve the hot starts and reduce vapor lock. The purge valve
helps. Smaller fuel restrictors also help.
As far as fuel lines go, all my lines FWF are flexible lines except for the
the stainless lines from the spider to the cylinders. If you use the
Airflow Performance system it is pretty straight forward and about as
simple as a purge valve can be.
My recommendation, if you don't have problems with hot starts, you don't
need a purge valve.
Bob
At 04:54 PM 10/2/06, you wrote:
| Quote: | Thanks for the writeup, Mike-
In deference to the KISS principle, how much hard evidence/experience is
there to support installation of a purge valve in an RV as opposed to
certified a/c where it may really be needed? Anyone tried starting their
hot IOs without it or done any actual testing to determine if it is really
a necessity, or something one "might" need once or twice a year under
worst conditions? Thinking here is to reduce fuel lines/fittings in a
REALLY bad spot to have a failure (and extra co$t) vs. a rare
inconvenience which is not a safety-of-flight issue...
Mark do not archive
|
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chaztuna(at)adelphia.net
Guest
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| Posted: Tue Oct 03, 2006 4:12 am Post subject: I've sworn off purge valve installations |
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Mike,
I have to agree with the other lister who suggested that your use of bulkhead connections mounted to the baffles is the most likely cause of your cracked tube problems. Due to the fact that the baffles are not supported at their top edge, they will vibrate at a frequency which differs from the rest of the engine. This will cause flexing of the lines ( be they SS, 3003 Versitube or 5052-T0 ). You also aggravated the situation (judging from your photo) by the way you bent that inboard tube. Your outer tube is formed the proper way. In high vibration environments, it is unwise to "cut the corner" with a tubing run. Big radius bends are better than small radius bends. Often, a service loop of tubing is advised, to help absorb vibration. Regardless of these secondary issues, the best choice would have been to use flex hose. Tubing is impractical in this area, because there is no practical place to mount a bracket for the bulkhead fittings to the engine itself.
The purge valve is mounted to the crankcases. The cylinders vibratory movement also differs from the crankcases, so even a bulkhead plate mounted to a cylinder would eventually cause a tubing failure near the bulkhead fitting B nut..
Charlie Kuss
[quote] It would have been. But late in the build cycle, I met and became best friends with a Delta mechanic who came into my project late and nearing the first flight. He said “I aint letting you up there with that el cheapo “Oh” tube as he called it. He proceeded to rip out every soft aluminum tube I had and replaced it with stainless steel. Every piece! Dozens of them! He was a master with this stuff and could take a couple measurements with a steel ruler, and come back with a perfectly fitted SS aircraft tube ready to go. Years in the hydraulics shop at the Delta hub here in Atlanta and I guess you get pretty good with this stuff. So I originally had in this picture here soft 3003, but it was replaced with stainless steel. I pointed the arrow to where the crack was. Right behind the b-nut sleeve. Again the pic, from a vintage late 90’s digital camera that only geeks were using at the time, is of soft tube but it was SS that cracked ~800 hours as I recall.
http://www.mstewart.net/deletesoon/engtopcrack.jpg
My theory was that flex line should absolutely have been installed here. That spider was no doubt bobbing around hung out there so far, while the rear baffle was not moving much at all I suspect.
Mike
From: owner-rv-list-server(at)matronics.com [ mailto:owner-rv-list-server(at)matronics.com (owner-rv-list-server(at)matronics.com)] On Behalf Of Charlie Kuss
Sent: Monday, October 02, 2006 11:49 AM
To: rv-list(at)matronics.com
Subject: Re: I've sworn off purge valve installations
Mike
Thanks for your report. Could you tell me what type of aluminum tubing you had used on your previous RV? Was it the 3003 Versitube which Vans supplies? Or something else. Do you have any theory on why that fuel line cracked?
Charlie Kuss
After my second failure in a couple thousand hours of running fuel injection with pruge valves, I have concluded they are unnecessary and can have multiple failure modes that can bring you down.
As many of you know Airflow Performance of Spartanburg SC sells a terrific fuel injection system for all kinds of engines. from boats, to dragsters, to planes. I have had their system on 2 RV’s and have had 2 failures in the purge system. The purpose in the purge valve is simple. On a hot start, pull the valve, turn your pump on, and allow the hot vapors out for a few seconds. Close the valve and start your normal hot start procedures.
On my RV-6 I had the purge vale return line running into the cockpit and into a tee on the fuel inlet near the tank selector switch. AFP recommends this returning back to the tank, but I felt this to be too complex an installation. One day, while scudding back from SnF, close to home base, with Michelle in the right seat, the engine coughed and would barely run. I managed to limp home. After weeks of troubleshooting, it turned out that I had a crack in a tube FWF on the purge return line. This crack was allowing air into the return line, and hence air into the fuel flow to the engine. After this incident I decided on my next plane, I would NOT put the purge return line into the fuel supply system. This failure could have put me and my wife in the trees.
On my 8, I ran the purge return into the left tank vent. Thought being, let the vapors and a little fuel run to the ground. Don’t let a line leak here spoil my fuel. So on a trip last week with several RV’s and wifes to NYC for a play and a movie, plane died on landing rollout in NJ. ARGH! We finished our weekend getaway with the wife’s, but on Sunday I put wife on a Delta flight home and began troubleshooting. What I found was the plane was way lean in running and would barely idle below 1500. I removed the fuel inlet to the servo and there was plenty of fuel going in, but the engine was not getting it. I checked screens and a few other things and no joy. I decided it was the servo not metering the fuel properly. I finally decided I try taking off and climbing to altitude and see if mother nature would richen it with altitude. Sure enough, around 7k’ I would get egt’s at peak, and at 10k’ I could run a little ROP. BUT the fuel flow was +4gph more than normal. How could that be? I dunno, but it was running smooth and I flew her home to Atlanta.
Safe in my own hanger, I removed the servo and flow divider and sent it to AFP. Don returned it with no problem found. ARGH! Spent the weekend troubleshooting and found the problem. The Purge valve was leaking internally and some fuel was by passing and going to the return side. Actually a lot of fuel was going to the return. This was causing lean operation and high fuel flow. I have now sent this to AFP for repair. I also suspect that this valve has been sending fuel to the return all along in the past 300 hours. I have gotten from day 1, and unexplained +1.5gph with my boost pump on.
In a couple thousand hours of RV injected operation in multiple aircraft, I have not found I needed this purge valve function for hot starts. In fact all I really use it for is to shut down the engine. Hot starts are easily handled with proper technique. I have now sworn off this purge valve madness as it provides no value in an RV and multiple failure modes.
Thought some of you might find this information useful.
Best,
Mike Stewart
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ronschreck
Joined: 04 Aug 2006
Posts: 192
Location: Gold Hill Airpark, NC (NC25)
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| Posted: Tue Oct 03, 2006 4:34 am Post subject: I've sworn off purge valve installations |
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I have been flying the AFP controller with purge valve for almost 140 hours now and have come to the conclusion that the purge valve is not required on hot starts. I turn the engine over with the mixture full lean until it fires and slowly move to rich as it smoothes out. I do use the purge valve for shutdown as the mixture does not fully shut off fuel delivery to the engine. I have run hose from the purge valve, through the baffles to a bulkhead fitting on the firewall. No hard fuel lines firewall forward.
Ron Schreck
RV-8, "Miss Izzy"
Gold Hill Airpark, NC
av8er2fly(at)peoplepc.com wrote: > What would your normal start be with out the purge valve? I do not > have a purge valve but was considering putting one on because of real > hard hot starts. Any Ideas would be appreciated. Mark Rose RV8A > 137MR IO360 85 fun Hrs. > Well, it all depends on what's causing the hard starts when hot. This will take some sleuthing on your part. The problem may be that it takes some extra pump time to fully pressurize the system and get fuel through the injectors. The problem may not be vapor in the lines. When you have a hot start problem have someone look at the exhaust. If you see vapor (think the wavy view of the air down a hot road) and it doesn't start than it's too rich and when it does start then you'll see black smoke out the exhaust. If you don't see anything, keep hitting the boost pump ..... keeping track of how long the total pump run is ..... a second or two at a time until it starts ..... you'll need someone to watch that exhaust. If i
t still won't start, then it's time to pull some plugs to see if they're wet. If you suspect vapor lock .... the only cure is positive pressure on the system. I'm partial to the 'serial flow system' .... where the boost pump feeds the engine pump which feeds the controller. Others like the 'parallel flow system' and that's OK too ...... but being able to pressurize the whole system is, to me, the key. If you can mount your boost pump as low as possible in the cockpit ..... which shouldn't get as hot as the engne compartment ..... and keep it cool, positive head pressure is always available ..... unless you run the tank dry!!! Bottom line, the sequence you use in starting can be very important and it's just a learning (leaning???? ) curve 'till you find what the engine really likes. Good luck!!! Linn do not archive
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dbris200(at)sbcglobal.net
Guest
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| Posted: Tue Oct 03, 2006 7:22 am Post subject: I've sworn off purge valve installations |
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When you shut the engine down, residual pressure (caused by the pump stopping on the pressure stroke and heat) can cause fuel to flow into the cylinders after the engine stops, which contributes to the hot start problem. When you use the purge valve to shut down, all the fuel is diverted from the flow divider and goes back to the tank so there is NO residual fuel going into the cylinders, Just using the purge valve to stop the engine helps it start more easily.
I did not have a purge valve for the first 50 hours or so and I installed it because of the shut down problem with the AFP system and I could not believe how much easier it started when it was hot.
The purge valve was some of the best money I've spent on my airplane.
Dave B. -6 So Cal
EAA Technical Counselor
ronschreck(at)windstream.net (ronschreck(at)windstream.net) wrote: [quote] | Quote: | --> RV-List message posted by: <ronschreck(at)windstream.net> (ronschreck(at)windstream.net)
I have been flying the AFP controller with purge valve for almost 140 hours now and have come to the conclusion that the purge valve is not required on hot starts. I turn the engine over with the mixture full lean until it fires and slowly move to rich as it smoothes out. I do use the purge valve for shutdown as the mixture does not fully shut off fuel delivery to the engine. I have run hose from the purge valve, through the baffles to a bulkhead fitting on the firewall. No hard fuel lines firewall forward.
Ron Schreck
RV-8, "Miss Izzy"
Gold Hill Airpark, NC
av8er2fly(at)peoplepc.com (av8er2fly(at)peoplepc.com) wrote: > What would your normal start be with out the purge valve? I do not > have a purge valve but was considering putting one on because of real > hard hot starts. Any Ideas would be appreciated. Mark Rose RV8A > 137MR IO360 85 fun Hrs. > Well, it all depends on what's causing the hard starts when hot. This will take some sleuthing on your part. The problem may be that it takes some extra pump time to fully pressurize the system and get fuel through the injectors. The problem may not be vapor in the lines. When you have a hot start problem have someone look at the exhaust. If you see vapor (think the wavy view of the air down a hot road) and it doesn't start than it's too rich and when it does start then you'll see black smoke out the exhaust. If you don't see anything, keep hitting the boost pump ..... keeping track of how long the total pump run is ..... a
second or two at a time until it starts ..... you'll need someone to watch that exhaust. If i
t still won't start, then it's time to pull some plugs to see if they're wet. If you suspect vapor lock .... the only cure is positive pressure on the system. I'm partial to the 'serial flow system' .... where the boost pump feeds the engine pump which feeds the controller. Others like the 'parallel flow system' and that's OK too ...... but being able to pressurize the whole system is, to me, the key. If you can mount your boost pump as low as possible in the cockpit ..... which shouldn't get as hot as the engne compartment ..... and keep it cool, positive head pressure is always available ..... unless you run the tank dry!!! Bottom line, the sequence you use in starting can be very important and it's just a learning (leaning???? ) curve 'till you find what the engine really likes. Good luck!!! Linn do not archive
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shempdowling2(at)earthlin
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| Posted: Tue Oct 03, 2006 8:09 am Post subject: I've sworn off purge valve installations |
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I just flood my io360 for about 3 seconds to push nice cool fuel through the
lines, then use standard flooding practices to start it. Full throttle,
full lean, crank till it begins to catch and reverse the throttle and
mixture levers. My rv runs HOT and this procedure has worked every time.
Shemp/Jeff Dowling
RV-6A, N915JD
300 hours
Chicago/Louisville
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mstewart(at)iss.net
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| Posted: Tue Oct 03, 2006 9:36 am Post subject: I've sworn off purge valve installations |
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Ditto Jeffs procedure. But I do that on my second try.
First try is lean, crack throttle, pump on, crank, count 5 blades, shove
mixture rich and it usually catches. If I wait till it catches before I
shove the mixture fwd, im usually too late. If that failes, try 2 is
method below.
BTW, the discussion on the usefulness of the purge valve should in no
way be seen as a dig against AFP. There system is solid and the company
is a pleasure to work with. Don took my call last week on a Friday at
6pmest to help me troubleshoot. They are a class act and I have not once
heard a bad word about them and their systems are everywhere.
I will reiterate that the purge valve setup adds complexity and failure
modes which are not off set by the benefits IMHO. Whether or not you
conclude builder error or not on a line here or there, there are failure
modes to be considered against the benefit of the valve and its
associated plumbing. My conclusion is that in MY EXPERIENCE, it is not
needed and therefore should be excluded from installation in RV's.
Mike
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dasduck(at)comcast.net
Guest
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| Posted: Tue Oct 03, 2006 1:26 pm Post subject: I've sworn off purge valve installations |
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I do similar to Mike, but usually 'prime' 2 or 3 seconds with pump on and
thr/mix in. Then pump off, throttle at appx 1200rpm (cracked), mixture lean
and push-in slowly after a few blades.
Leaving the oil door open while fueling and paying the bill can do a lot to
reduce heat build-up under the cowl as well.
Don RV-6, 12 years with AFP, no purge.
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kahuna
Joined: 02 Feb 2007
Posts: 93
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| Posted: Fri Feb 02, 2007 10:21 am Post subject: Re: I've sworn off purge valve installations |
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Well here I am again with this topic because I have some new data for you. Last month an RV-4 N360WS, based at my airport, had an engine failure while enroute and landed in a field. Pilot had his 10 yr old son with him. Both are ok. Plane is totaled. FAA has just completed its findings. PURGE VALVE FAILURE. Yep thats right. The pilot/builder did the same thing I did. Mounted and plumbed it without knowing that the little screws had to be safety wired. I was fortunate. HE was not. While he survived his off field, his show quality RV-4 is now in the heap pile.
He also did not use his valve except for shut down. So I ask you... What are the chances that this is some isolated problem. 2 guys, from the same field, within a month of each other, with a failure of the purge valve? You still think its edge case?
I say to you again, I have sworn them off my planes. Not needed on an RV, adds both complexity and failure modes.
And if you have not checked your purge valve for the screws being safety wired, I suggest you get right on it. Sorry to bring this up again, but I feel at least compelled to bring you the data.
See ya,
Mike
[quote="mstewart(at)iss.net"]After my second failure in a couple thousand hours of running fuel injection with pruge valves, I have concluded they are unnecessary and can have multiple failure modes that can bring you down.
As many of you know Airflow Performance of Spartanburg SC sells a terrific fuel injection system for all kinds of engines. from boats, to dragsters, to planes. I have had their system on 2 RV’s and have had 2 failures in the purge system. The purpose in the purge valve is simple. On a hot start, pull the valve, turn your pump on, and allow the hot vapors out for a few seconds. Close the valve and start your normal hot start procedures.
On my RV-6 I had the purge vale return line running into the cockpit and into a tee on the fuel inlet near the tank selector switch. AFP recommends this returning back to the tank, but I felt this to be too complex an installation. One day, while scudding back from SnF, close to home base, with Michelle in the right seat, the engine coughed and would barely run. I managed to limp home. After weeks of troubleshooting, it turned out that I had a crack in a tube FWF on the purge return line. This crack was allowing air into the return line, and hence air into the fuel flow to the engine. After this incident I decided on my next plane, I would NOT put the purge return line into the fuel supply system. This failure could have put me and my wife in the trees.
On my 8, I ran the purge return into the left tank vent. Thought being, let the vapors and a little fuel run to the ground. Don’t let a line leak here spoil my fuel. So on a trip last week with several RV’s and wifes to NYC for a play and a movie, plane died on landing rollout in NJ. ARGH! We finished our weekend getaway with the wife’s, but on Sunday I put wife on a Delta flight home and began troubleshooting. What I found was the plane was way lean in running and would barely idle below 1500. I removed the fuel inlet to the servo and there was plenty of fuel going in, but the engine was not getting it. I checked screens and a few other things and no joy. I decided it was the servo not metering the fuel properly. I finally decided I try taking off and climbing to altitude and see if mother nature would richen it with altitude. Sure enough, around 7k’ I would get egt’s at peak, and at 10k’ I could run a little ROP. BUT the fuel flow was +4gph more than normal. How could that be? I dunno, but it was running smooth and I flew her home to Atlanta.
Safe in my own hanger, I removed the servo and flow divider and sent it to AFP. Don returned it with no problem found. ARGH! Spent the weekend troubleshooting and found the problem. The Purge valve was leaking internally and some fuel was by passing and going to the return side. Actually a lot of fuel was going to the return. This was causing lean operation and high fuel flow. I have now sent this to AFP for repair. I also suspect that this valve has been sending fuel to the return all along in the past 300 hours. I have gotten from day 1, and unexplained +1.5gph with my boost pump on.
In a couple thousand hours of RV injected operation in multiple aircraft, I have not found I needed this purge valve function for hot starts. In fact all I really use it for is to shut down the engine. Hot starts are easily handled with proper technique. I have now sworn off this purge valve madness as it provides no value in an RV and multiple failure modes.
Thought some of you might find this information useful.
Best,
Mike Stewart
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