TRASH in TANKS
 
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David Roth
Trusted Member

Well here I go with another fuel related question. 

I want to clean out the fuel tanks on my 108 as I am getting an unacceptable amount of debris in the fuel when I sump the tanks.  I don't know what the material is except that it is small flakes & particles of varying color.

I would like to drain them & then flush them out.  I assume that disconnecting the fuel lines from the tanks will be necessary so that whatever gets flushed out can be collected at the tank outlets. 

Does anyone have suggestions on how to go about this?  Should fuel be used as the flushing liquid so as not to contaminate the tanks with something else or is that too risky?

Again, thanks for all your help!  I'm kind of going over my, new-to-me, 72 year old plane with a fine tooth comb getting things up to snuff.

David

 

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Posted : 21/11/2019 4:13 am
resto108
(@resto108)
Estimable Member

Due to the one way flapper valves that are probably still in place, the only right way to flush the tanks is to take them out.

tank

 

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Posted : 21/11/2019 10:51 am
David Roth
Trusted Member

Thanks for the reply!  Don't know if the one way flappers are still installed.  I'll have to check that out.  I hope I can find a means of cleaning the tanks without removal.  That would be a big job!

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Posted : 21/11/2019 2:59 pm
Bob Pustell
Eminent Member

You can usually hear your flapper valves. If you gently rock the wings while the plane is sitting still on a level surface you will usually hear a sort of clicking or gentle muffled clanking sound. That is the one way flapper valves opening and then slamming shut as the fuel tries to move sideways one way and then the other with the sloshing. The flappers are intended to minimize the fuel moving out towards the wingtips, they are trying to keep the fuel at the inboard end of the tank where the fuel lines are connected to the tank connections. Folks whose flappers have come off their hinges have done one of two things -- either they operate without them (and have generally done just fine) or they need to replace the tank(s) or cut them open to put new hinges onto the flappers. That might even be the source of your particals - the flapper hinge rod is steel or iron and sometimes rust away to nothing over the years, I am told. That last is second hand info - I have never held a flapper hinge in my hand to see what metal it is made of, personally.

Bob and Pat and the two Stinsons

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Posted : 22/11/2019 2:42 am
domurray
Eminent Member

David,

I suspect it could be several things giving particles to the system like old deteriorating gaskets or rubber/cork from the fuel senders, rust ( inside fuel fill neck), and wore out flappers. If you drain the tank by removing the sump plug then look with a borescope into the tank to see the condition. I just got my tanks back from Hartwig because one was leaking but flappers were also worn through hinges. The tanks look good but in all honesty it would have been cheaper to buy new ones from univair because of shipping costs.Don

984D9D61 E046 4B43 A1B3 888FCE93273A
7437E725 B7DF 448C 9C9D 87A25DACCE7A

 

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Posted : 22/11/2019 12:12 pm
Will Ware (Webmaster)
Member Admin
Posted by: @resto108

Due to the one way flapper valves that are probably still in place, the only right way to flush the tanks is to take them out.

tank

 

Wow, I never even knew that there were flapper valves in there. Always like learning

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Posted : 24/11/2019 4:26 am
Will Ware (Webmaster)
Member Admin
Posted by: @domurray

David,

I suspect it could be several things giving particles to the system like old deteriorating gaskets or rubber/cork from the fuel senders, rust ( inside fuel fill neck), and wore out flappers. If you drain the tank by removing the sump plug then look with a borescope into the tank to see the condition. I just got my tanks back from Hartwig because one was leaking but flappers were also worn through hinges. The tanks look good but in all honesty it would have been cheaper to buy new ones from univair because of shipping costs.Don

984D9D61 E046 4B43 A1B3 888FCE93273A
7437E725 B7DF 448C 9C9D 87A25DACCE7A

 

Is the green tank yours Don? Is it one of the new ones you mentioned?

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Posted : 24/11/2019 4:26 am
David Roth
Trusted Member

@stinsono

Speaking of one way flapper valves.  What the heck are they, where in the tank are they & what exactly do they do?  Thanks!

David

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Posted : 24/11/2019 4:32 am
Will Ware (Webmaster)
Member Admin

Well, I’m assuming that they keep the fuel from “Sloshing” in the tank. If you look at the picture above that @Resto108 posted, you can see them

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Posted : 24/11/2019 4:40 am
lawheelock
Honorable Member

While this thread started with questions about trash in the fuel tanks, I can think of a couple of reasons why there might be trash in the fuel tanks. First, someone at some point in the aircraft's history may have attempted to stop a tank from leaking by pouring in "sloshing" compound, long a means of sealing leaking tanks in the old days of automobiles and farm tractors.  It was designed to coat the inside of the tank to seal seeps and minor leaks.  Today's fuel has solvents in it that were not there in the old days and if a tank has been "sloshed" years ago, today's fuel will most likely loosen that material and it will flake off.  Like paint remover.

A second possibility is that ethanol laced auto fuel has been used over a long period of time probably with months or years of inactivity and the moisture that the ethanol sucks in can form acids that corrodes the aluminum tanks and particles of corrosion will start showing up. 

Then a third possibility is simply that someone has used dirty containers to fuel the plane and did not take precautions in keeping the fuel clean.

About the only way to adequately clean out a fuel tank is to remove it from the plane.  Starting on page 99 of the Stinson 108 series general service manual, the fuel system is described and on page 100 fuel tank removal is covered and repair and installation follow.

What isn't covered is that the tanks must be reinstalled without being covered with fabric and the proceedures followed in AD 49-18-02 which technically only applies to 108-2 and -3 models should be followed with tank installation in any 108 re-installation.

Now, about those flapper valves.  There is two in each tank.  The picture above is of a tank laying on its top and the one intact flapper is hanging down.  It is a disc of aluminum  about 1/8" or more in thickness with a protrusion that has a hole drilled through it to insert a wire to form a hinge.  The flappers are on the inboard internal tank rib.  There are several internal ribs in the tank.  The inboard one has two holes with the flapper valves on the inboard side of the rib that hang down to help prevent "unporting" of the fuel if a takeoff is made in a curving direction like often is the case in seaplane operation to prevent the fuel, if the tank is low on fuel from going to the outside of the tank and preventing adequate fuel to drain out the fuel line port.  Stinson Service letter #70 titled Seaplane Operation describes the cautions to be taken, it does not mention the flapper valves, but that is what they are there fore.  If the hinge hole or wires have disconnected and the flapper dropped to the bottom of the tank, no harm will come unless you are in the habit of taking off on a curved runway or in a seaplane taking off in a curved path and feeding your engine from the tank on the outside of the curved path resulting in centrifugal force exerted on the fuel forcing it to the outside of the curved path.  Unless you have a seaplane or operate from curved runways, it is not worth the expense and effort to cut the tank apart and fabricate new flapper valves or their mounting hinges,

 

 

 

 

 

This post was modified 10 months ago by lawheelock

Larry Wheelock, A&P/IAStinson 108 N584LW 180 LycTexas in Winter; Indiana in Summer

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Posted : 24/11/2019 7:03 am
domurray
Eminent Member

@stinsono

It is my recently refurbished tank ready to put back in the plane. The cost was within 100 bucks of just buying a new tank from univair for $1500. Don

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Posted : 24/11/2019 12:13 pm
Will Ware (Webmaster)
Member Admin
Posted by: @domurray

@stinsono

It is my recently refurbished tank ready to put back in the plane. The cost was within 100 bucks of just buying a new tank from univair for $1500. Don

Thanks Don. Did you refurbish yourself, or did you send it off? I was considering Hartwig for mine.

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Posted : 24/11/2019 12:56 pm
domurray
Eminent Member

I sent it to Hartwig. Quoted me $650 to ship them back and I live in the same state. I didn’t pay that to get them back but if I had to do it over again I would have bought new and got the free shipping from univair.

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Posted : 24/11/2019 3:32 pm
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