Problem removing fuel cap

[Yooper Rocketman]

OK, so I was out to the airport and took a picture of the culprit.  The first one shows the baffle closed just below where the cap installs.

 

 

This next one shows the baffle held open.

 

 

This last one shows the o-ring in the bottom of the filler neck, as seen through a mirror.

 

 

Unless someone has a better idea, I think the best solution is to cut a nick in the o-ring.  Thinking about this, if the spring loaded baffle actually seals, and you go up really high into thin air, the air in this cavity will purge down into the tank past the baffle,  You come back down to the ground and now this air is thin and trying to suck heavier air back in to this cavity.  If the cap seals, as it should, and the baffle seals, as it should (which I guess most don't), then this problem was designed right into system.  And to think I could have been an engineer.

[orionflt]

the better design would be to have it so the nut from the fuel cap keeps the flapper valve from seating completely when the cap is installed, when the cap is removed or missing it would be allowed to fully seat. that would eliminate your problem without any major mods, the question is how much clearance is there currently between the cap and flapper.

 

Brian 

[Yooper Rocketman]

the better design would be to have it so the nut from the fuel cap keeps the flapper valve from seating completely when the cap is installed, when the cap is removed or missing it would be allowed to fully seat. that would eliminate your problem without any major mods, the question is how much clearance is there currently between the cap and flapper.

 

Brian 

Good point, but no where near close.  I would guess at least an inch.

[DonMuncy]

Live and learn. I had no idea there was an O-ring in there. I will have to look and see if mine have one.

[Yooper Rocketman]

Live and learn. I had no idea there was an O-ring in there. I will have to look and see if mine have one.

 

Yep Don, I didn't know either until running my fingers under the lip.  I always thought it was just a metal on metal contact, to slow fuel leakage in the event of a lost cap.  

[DonMuncy]

Don't you wonder how many planes have O-rings floating in their tanks.

[Hank]

Don't you wonder how many planes have O-rings floating in their tanks.

Only those of you with fancy planes that have fuel flapper. My C does not. ☺ Oh, the joys of flying vintage!

[chrisk]

the better design would be to have it so the nut from the fuel cap keeps the flapper valve from seating completely when the cap is installed, when the cap is removed or missing it would be allowed to fully seat. that would eliminate your problem without any major mods, the question is how much clearance is there currently between the cap and flapper.

 

Brian 

 

 

I think the whole reason the flapper is on the plane is because it is possible to put the fuel cap on in an unaligned way.  I've had linemen do this to my plane twice.  And when it happens, I need a screwdriver to get enough leverage to pop the lever up.  I can't imagine the cap seals very well.  Without the flapper, you might lose considerable fuel.

 

I suspect a cap could be made with a plunger or expanding region. Kind of like the valve on an inner tube.  This would relieve enough pressure to break the vacuum created between the cap and flapper.  I can envision a way to modify an existing cap, but I really couldn't see an STC being reasonable. I'd use a presta valve core. 

[Houman]

I have a Rocket and excatly the same setup as you and never ran into this issue. Personally I would be very reluctant to make a whole or nick the ring and get wather into the fuel.

How hi do you fly, I have flown up to fl160 and never had this...

[chrisk]

I've had the problem with out ever flying the plane. Fueled it when I came back from a flight. Two days later it was a bitch to get the cap off for a preflight. Tank was FULL to the very top. I could not put the cap on with out spilling fuel after the preflight.

[Yooper Rocketman]

I have a Rocket and excatly the same setup as you and never ran into this issue. Personally I would be very reluctant to make a whole or nick the ring and get wather into the fuel.

How hi do you fly, I have flown up to fl160 and never had this...

How would you get water in by nicking the o-ring on the baffle? It would still need to get by the fuel cap and that is obviously sealing well, or I wouldn't have this problem in the first place.

I routinely see FL 230 &. 240. I never had an issue during the first 1000 hours on this plane either.

[Guest]

How would you get water in by nicking the o-ring on the baffle? It would still need to get by the fuel cap and that is obviously sealing well, or I wouldn't have this problem in the first place.

I routinely see FL 230 &. 240. I never had an issue during the first 1000 hours on this plane either.

After having read and posted lots here, it is very obvious that there are vast differences in what people know or don't know about their airplanes.

I think that Houman is referring to the fuel cap O ring, while you are referring to the O ring on the bottom of the filler neck which seals the anti siphon flapper.

Clarence

[carusoam]

Clarence,

A big challenge is there are not that many anti-siphon flappers on the different Mooneys...

Any idea if they are K only, or part of extended fuel tanks or what their intended value is?

The original tank/cap design with SS parts and modern O-ring materials seems to work pretty well.

Caps are too expensive to leave behind and easy enough to pre-flight...

If you notice that the cap has been left behind during the taxi, would it be OK to continue to take-off?

It seems more like a solution to a problem we don't really have?

Adding good seals to this system is going to create the vacuum challenge.

Fixing the vacuum challenge by compromising the cap seals turns into a rain water intake risk.

I am not familiar with this system, but I'm curious about all things Mooney.

I would be guessing that the flapper isn't supposed to have a perfect seal. There is probably a Mooney (or other) part diagram with a part number to define it? Possibly the last annual it got replaced with a more standard seal...

Best regards,

-a-

[N201MKTurbo]

I think the flapper valve is a solution looking for a problem. Some engineer at Mooney back in the day must have had a brother in law in the flapper valve business.

[Yooper Rocketman]

After having read and posted lots here, it is very obvious that there are vast differences in what people know or don't know about their airplanes.

I think that Houman is referring to the fuel cap O ring, while you are referring to the O ring on the bottom of the filler neck which seals the anti siphon flapper.

Clarence

M20Doc,

You have hit the nail on the head. But, in all fairness,someone not familiar with this system would have a hard time grasping the problem. M201MKTurbo also hit the nail on the head. An engineer searching for a problem that didn't exist created another problem.

[Nemesis]

M20Doc,

You have hit the nail on the head. But, in all fairness,someone not familiar with this system would have a hard time grasping the problem. M201MKTurbo also hit the nail on the head. An engineer searching for a problem that didn't exist created another problem.

Yooper and Doc,

 

Siphoning of fuel at higher altitudes has been a problem for decades. I think the Mooney anti-siphon valve is a pretty good and simple solution.

My K does not have the vacuum problem that you describe so I must have just a slight leak into that cavity that relieves the vacuum.

However, I remember posts in some other thread asking about a small hole located high in the outboard side of the filler neck in newer Acclaims and Ovations.

I sort of remember the conclusion of those posts was about air relief during fueling but now that I have read about your problem, it is much more likely that it was a solution to vacuum locked fuel caps.

So, I would try to track down a couple of owners of newer aircraft and ask them. An A&P with a current set of parts manuals might be a good source as well.

Maybe a call to Dmax or Paul Loewen at LASAR might help too.

 

Dave

[Yooper Rocketman]

Clarence,

A big challenge is there are not that many anti-siphon flappers on the different Mooneys...

Any idea if they are K only, or part of extended fuel tanks or what their intended value is?

The original tank/cap design with SS parts and modern O-ring materials seems to work pretty well.

Caps are too expensive to leave behind and easy enough to pre-flight...

If you notice that the cap has been left behind during the taxi, would it be OK to continue to take-off?

It seems more like a solution to a problem we don't really have?

Adding good seals to this system is going to create the vacuum challenge.

Fixing the vacuum challenge by compromising the cap seals turns into a rain water intake risk.

I am not familiar with this system, but I'm curious about all things Mooney.

I would be guessing that the flapper isn't supposed to have a perfect seal. There is probably a Mooney (or other) part diagram with a part number to define it? Possibly the last annual it got replaced with a more standard seal...

Best regards,

-a-

A couple answers;

I bought the plane with standard tanks, had the extended ones added while re-sealing all tanks down in Fort Lauderdale.

I know the seals have not been changed on either the caps or the flappers since this problem started. Agree with last poster that some type of relief hole is the answer, but not easy to do considering you will need to deal with drill filings possibly getting into the fuel tank.

[Guest]

A couple answers;

I bought the plane with standard tanks, had the extended ones added while re-sealing all tanks down in Fort Lauderdale.

I know the seals have not been changed on either the caps or the flappers since this problem started. Agree with last poster that some type of relief hole is the answer, but not easy to do considering you will need to deal with drill filings possibly getting into the fuel tank.

While drilling the vent hole most of the chips will land on top of the flapper, easily cleaned up. It is only when drilling completely through that chips can enter the tank. To minimize this apply grease to the flutes of the drill bit to catch the drilling chips. Something sticky like seal lube works also, the stickier the better.

Clarence

[Yooper Rocketman]

While drilling the vent hole most of the chips will land on top of the flapper, easily cleaned up. It is only when drilling completely through that chips can enter the tank. To minimize this apply grease to the flutes of the drill bit to catch the drilling chips. Something sticky like seal lube works also, the stickier the better.

Clarence

Thanks Clarence. I think the most sense is to drill a small hole in the aluminum neck. When I get back from Punta Cana, I will see if my angle drill will fit inside the neck to perform that repair.

[DonMuncy]

I had a chance to look at my 231 today, and found it does not have "O"rings at the anti- syphon flapper. Unless someone sneaked them out at an annual, the plane has not had them since I bought it in 2000. Does anyone know the specifications for these O-rings. Other than the risk of dropping one in the tank, I don't see that it would be any problem to install them.

[Yooper Rocketman]

Don,

 

I would not say a thing.  You'll be dealing with the same problem as me if you install o-rings.

[carusoam]

Recycling through the ideas...

1) good cap seals and a good flapper seal cause a vacuum challenge...

2) a good flapper seal doesn't make strong sense, because fuel cap seals work as designed and are easily replaced when they age.

3) the anti-siphon flap would work if the tank's cap fell off or the cap's seals degrade.

4) it is a challenge to fill the tank to the top if the fill neck is not vented.

5) if filling the tank to the top ( not part of the filling procedure), and having bad seals, some fuel does get siphoned out leaving a blue stain on top of the wing.

6) adding the extended outboard tanks adds to the importance of the filling process. Leaving the cap off the inboard tank may lead to fuel running out the top while filling the outboard tanks?

7) does the outboard cap have the same or similar anti-siphon flap?

8) there are few flapper equipped Mooneys. There is even fewer reporting having a sealed flapper.

9) having a vent hole added above the sealed flapper would negate any value that the flapper or the seal may have added.

10) having a vent hole and leaving the seal on the flapper would potentially lead to fuel being locked on top of the sealed flapper. A consideration for useable fuel in the tank if this were to occur...

11) I see some challenges being generated by the sealed flapper and not much benefit. It would make me be sure that the seal is there for a reason and that I got the correct parts.

12) Drilling a hole could possibly defeat the purpose of the sealed flapper, and would be expensive to replace.

This is only a collection of the thoughts presented in this thread. I am only a private pilot. I don't have a flapper on my tanks.

I am genuinely interested in the logic behind the sealed flapper...

Best regards,

-a-

[Yooper Rocketman]

My comments in bold

 

Posted Today, 10:28 AM

Recycling through the ideas...

1) good cap seals and a good flapper seal cause a vacuum challenge...  If everything seals tight

2) a good flapper seal doesn't make strong sense, because fuel cap seals work as designed and are easily replaced when they age. Agree

3) the anti-siphon flap would work if the tank's cap fell off or the cap's seals degrade. Will not help if the main fuel cap seal is bad, as water would get to this paddle  and would enter tank if touched (deflected down) for fueling.  It would work if cap fell off keeping fuel from porting off.  That was what the design was incorporated for.  Must be less gained than lost with design, as I see no other GA planes using this system.

4) it is a challenge to fill the tank to the top if the fill neck is not vented.  It's a challenge without it vented.  Each tank will hold 4 more gallons after fuel reaches the bottom of the neck.  The only way to get the last 4 gallons in is to add the fuel really slowly so the tank can vent the air out the tank vent as you fill it.  This was a real issue before installing extended range tanks, as those last 4 gallons almost always figured into my reserves, which meant I either self fueled, or had to supervise the filling.  No line guys would ever fill it completely unless supervised.

5) if filling the tank to the top ( not part of the filling procedure), and having bad seals, some fuel does get siphoned out leaving a blue stain on top of the wing.  Total fuel capacity, as documented in the POH, considered the tanks fueled to the top, not to the bottom of the neck.

6) adding the extended outboard tanks adds to the importance of the filling process. Leaving the cap off the inboard tank may lead to fuel running out the top while filling the outboard tanks?  Not a problem.  I DO have to fuel inboards first, then extended tank, then back to inboard, filling very slowly so air can vent through fuel tank vent, then back to extended one last time.  Never had fuel come out "inboard tank" when extended tank was filled to top.  Suspect flapper paddles stopped that.

7) does the outboard cap have the same or similar anti-siphon flap?  No, normal fill neck.

8) there are few flapper equipped Mooneys. There is even fewer reporting having a sealed flapper.

9) having a vent hole added above the sealed flapper would negate any value that the flapper or the seal may have added.  Yes, but would relegate fuel filler to "normal" or "typical" fuel neck.

10) having a vent hole and leaving the seal on the flapper would potentially lead to fuel being locked on top of the sealed flapper. A consideration for useable fuel in the tank if this were to occur...   Happens all the time now.  I always open my fuel tank and have fuel on the one tank with the good flapper seal.  I've even had line guys come back and tell me I don't need fuel saying "it's already full".  I tell them to push the fuel nozzle in and open the flapper and the fuel drops into the almost empty tank.  The fuel in this area amounts to a bit more than a cup (12 oz), so not a big deal.  It's a welcome trade given I started with 4 more gallons by completely filling the tank.

11) I see some challenges being generated by the sealed flapper and not much benefit. It would make me be sure that the seal is there for a reason and that I got the correct parts.   Yep, it's there because some engineer or lawyer determined they needed to incorporate Dumb Sh.t Valves, for the D.S. that is stupid enough to take off in a LOW WING (where you can see the caps even if you don't do a walk around) with the fuel caps off.  The very fact no GA planes today incorporate this feature pretty much sums up the value of this feature.

12) Drilling a hole could possibly defeat the purpose of the sealed flapper, and would be expensive to replace.  I have resigned that I will not do that.  I MAY have the 0-rings "disappear" at the bottom of the necks, like Don's.  At least, by doing that, I can re-install them and will have not permanently violated anything on the airplane.  It's getting really old having to personally assist every fueling because the line guys can't get the cap off (or worry they will use a screwdriver to remove it).

This is only a collection of the thoughts presented in this thread. I am only a private pilot. I don't have a flapper on my tanks.

I am genuinely interested in the logic behind the sealed flapper...

Best regards,

-a- 

[carusoam]

Tom,

Thanks for taking the time to fill in the details.

Best regards,

-a-