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07-11-2014, 06:09 AM
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Join Date: Oct 2005
Location: 08A
Posts: 9,500
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Quote:
Originally Posted by vic syracuse
I don't know how much clearer I can be here. This is a dangerous configuration that will eventually bite you.
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....the operative word being "configuration".
Quote:
Originally Posted by C-FAH Q
I have had one valve fail, luckily it failed in an open position.
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I've examined a cheap POS valve that was failed open, as delivered, brand new in a kit. Not cool. Got a photo of yours?
__________________
Dan Horton
RV-8 SS
Barrett IO-390
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07-11-2014, 07:22 AM
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Join Date: Apr 2012
Location: Tampa (BKV)
Posts: 926
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Quote:
Originally Posted by C-FAH Q
I have had one valve fail, luckily it failed in an open position. I have also had my spigot coke over, which then produced leaks all over the place. I have since disconnected it and will not be hooking it back up. I like the idea of the valve, it just needs to be made fail safe but not sure how that would be done. I think Rocket bob has used a wet vacuum pump to pull a vacuum on the case, that maybe the answer?
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How many hours did it take to coke over? How many did the valve last? Where were you tapped into the exhaust?
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RV-8 Flying
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2015 Sun n Fun Kit Built Reserve Grand Champion
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07-11-2014, 08:05 AM
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Join Date: Dec 2008
Location: Ontario, Canada
Posts: 464
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Quote:
Originally Posted by ColoRv
How many hours did it take to coke over? How many did the valve last? Where were you tapped into the exhaust?
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The valve was attached 6" behind the ball joint where the two pipes join and 16" from the end of the exhaust pipe. It lasted about 20 hours and ASA shipped me a new one no charge. Time to coke over was about 40 hours.
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07-11-2014, 09:26 AM
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Join Date: Sep 2007
Location: Central IL
Posts: 5,516
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Quote:
Originally Posted by vic syracuse
OK, I've been thinking about his all day and have done some research, so I am going to express a much stronger opinion, and I understand that some may not be comfortable with it. I'm OK with that and I'll tell you why.
I believe very much in all of the Experimental aviation we do. However, sometimes there becomes enough data that points to a potential safety problem. I have spent the last year chasing down everything I could thing of that could be wrong with my engine, because others on this board, and even certain suppliers, stated that no one else is having this problem, so it must be me. I had occasion today to get some advice from "old-timers" who claim that this setup was tried 30 years ago by a number of them and they had nothing but coking problems, so they all removed them.
Looking back, I think one of the differences is not with my "setup" but the fact that I fly it A LOT. I fly 200-300 hours per year, and take long trips like this current trip to Alaska, where we will put 50+ hours on it. I believe I am seeing things that ALL of you with this setup are eventually going to experience, and that is coking within 30-50 hours. There are already a few of you in this thread who have reported it.
It is true that we are experimenters, and I also believe the axiom that "we stand on the shoulders of giants." It has become clear to me today that some of the giants have already had bad experiences with this setup.
Here's my concern for those of you running this setup, especially without a safety valve. With a lot of local flying, 1-2 hours at a time, maybe 20-30 hours per years, you won't see this issue rear it's ugly head until you decide to take that long cross-country to OSH, to the Bahama's, or to Alaska, where you will very quickly add the 20-50 hours where the coking WILL show up. Without the safety valve, the odds are you could have a very serious problem before you catch it, including a blown nose seal and the commensurate loss of oil pressure.
No, there is nothing wrong with the valves. There is most likely nothing wrong with the air/oil separator (I don't even have it installed this time. I have duplicated the problem with and without the separator). This is a problem with attaching the output of the breather tube to the exhaust system. And yes, Dan, mine is aft of the muffler on the RV-10.
Against my best judgment I made this change again before a long trip to Alaska. I broke my own rule of no changes at the last minute, but at least Dan's safety valve worked. Someone must be looking out for me. So I feel obligated to pass along the experience and the warning. Please heed them.
Vic
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Bingo - - Oil going from a crankcase temps in a metal tube to exhaust temps will pass a coking temperature point somewhere. Period.
Knowing this and having it as a maintenance point or design a pressure relief can avoid trouble.
I investigated oil breather separators 30 years ago when working at Conti. My friend and super engineering guru there said most of these just don't work . . . I was challenged.
I found that in theory and practice it takes surface area to truly coalesce the aerosols to a liquid and allow them to drip down. Higher blowby will drive the oil out, then a larger container is needed. Our Lycs don't typically have a lot of blowby. Here is the interior of the Airwolf, see the expanded metal for surface area?
Now, in the experimental arena, we have options. All of which are valid based on the requirements of the builder for under cowl space, cost, belly cleanliness, maintenance (safety), and oil retention.
Your Coefficients WILL Vary (YCWV) in how you weight the relative importance.
Everyone can be right, but should be fully aware of all the ramifications of the "configuration" they choose.
Full disclosure - I will be using the standard draft tube until my coefficients change, with some attention to a back flow angle ad DanH has illustrated previously. Sharing results with others helps us all understand and act accordingly.
FYI - The original Allison 1710 in the P51 had to drain, strain, and replenish the coolant every 10 hours. The engine TBO was 300 hrs. All according the the maintenance manual from the day.
__________________
Bill
RV-7
Lord Kelvin:
“I often say that when you can measure what you are speaking about,
and express it in numbers, you know something about it; but when you
cannot measure it, when you cannot express it in numbers, your knowledge
is of a meager and unsatisfactory kind.”
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07-11-2014, 12:38 PM
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Join Date: Mar 2005
Location: Tucson, AZ
Posts: 167
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I don't understand the idea that if a valve fails in a closed position, it could lead to blown seals.
Wouldn't the pressure of a closed valve be relieved through the oil return line to the engine?
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Roger, 7A, N374RS, Tucson
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07-11-2014, 02:16 PM
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Join Date: Oct 2005
Posts: 1,516
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The valve is the only path to the atmosphere.
The oil return leads to the crankcase. (same chamber as the one where the breather tube comes from)
If the valve stays closed the crankcase pressurizes to the point of blowing the front seal, the weakest tight spot in the system.
__________________
Ernst Freitag
RV-8 finished (sold)
RV-10 Flyer 600 plus hours
Running on E10 mogas
Don't believe everything you know.
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07-11-2014, 03:48 PM
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Join Date: Dec 2008
Location: Ontario, Canada
Posts: 464
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Quote:
Originally Posted by N427EF
pressurizes to the point of blowing the front seal, the weakest tight spot in the system.
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Or the silicon valve cover gaskets if you have them. 
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07-11-2014, 09:57 PM
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Join Date: Dec 2011
Location: Edinburg, TX
Posts: 617
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This whole thread got me to worrying about my installation so off to the hanger I went. I installed my anti splat vent system about 30 hours ago on my 160 hp rV9. Most of my flying was local with two trips. One to sun & fun about 1050 miles each way and another to north Texas about 500 miles each way. My valve and tube are located in the left exhaust tailpipe just in front of the firewall and about 12" from the end of the pipe. What I found was that there was already a small buildup or material deposit that was forming. The deposit was not inside the vent tube. It was however was forming immediately downstream of the vent pipe where it exits into the tailpipe. The deposit was somewhat pyrimidal in shape and about 1/4" high. I knocked it right off with a ling screwdriver and it would easily crumble when compressed by the fingers. While there was no buildup in the breather pipe itself there certainly were deposits forming in the tailpipe which is somewhat concerning. I'm taking dans approach tomorrow and installing a second vent line and check valve just in case. It appears there is enough evidence to support the additional precaution. I will also check the system now at each oil change for further obstruction and if found remove them. This system has been great in keeping my engine dry and belly clean. I don't want to give that up and a few minutes extra work at oil change time is a small price to pay. The secondary vent is there as a just in case so I should never suffer from a blocked vent. Just another point of data and my thoughts.
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RV-3 Rebuilding
RV-9 Flying and having fun, experimenting and having fun, did I mention flying and having fun?
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Maule M5-235C SOLD
C-172G SOLD
Stinson L5 SOLD
Grumman AA1A SOLD
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07-11-2014, 10:07 PM
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Join Date: Apr 2012
Location: West Fargo, ND
Posts: 1,073
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Quote:
Originally Posted by Jrskygod
This whole thread got me to worrying about my installation so off to the hanger I went...................... .
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Thanks for your input. So, any noticeable performance increase with this mod?
I wish others would chime in. Im particularly interested in those who have had no issues. I will monitor mine, i have the hose clamp version so it can be removed and reinstalled in about two minutes.
So, if you remove the reed valve from the tailpipe, where is a good spot to route the breather too then, AND how do you patch the big hole in the tailpipe
__________________
Derek Hoeschen
EAA Tech Counselor
RV-9A #92103 - N803DK
G3X, Superior XO-320, Dual Pmags, Catto 3B
www.mykitlog.com/dbro172/
1974 Bellanca Super Viking - N16AW - Flying
RV-8 #83565 - N184DK - building
1968 Mooney M20C - N6801N - Sold
1956 C-182 - N744W - Sold
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07-11-2014, 11:58 PM
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Join Date: Nov 2005
Location: San Francisco, CA
Posts: 525
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I just checked mine, too. Similar finding. Black carbon build up on the end of the pipe near the exhaust. I would estimate about 40 to 50% blockage with about 150 to 200 hours? I will certainly be checking it after each oil change from now on.
Area all around the valve itself is super clean. Installed in the exhaust pipe on the bend after the heat muff/muffler.

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#40533 RV-10 Builder and CFI
1/2006 Started build
10/19/2011 First flight
Last edited by jchang10 : 07-12-2014 at 09:38 AM.
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