Stupid pipe threads

bnt83

bnt83

Final Approach
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I so thought this was going to be a thread about stupid pipes.
 
Sac Arrow said:
I so thought this was going to be a thread about stupid pipes.
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Sorry, but its about these





I can think of at least a dozen joints in my fuel system that uses tapered pipe threads.


A real trick is correctly clocking an elbow and getting the pipe thread joint tight.

 
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GlennAB1 said:
Sorry, not on real airplanes.
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Can't recall ever seeing a pipe thread on transport category. (doesn't mean they aren't there)


I can think of over a dozen on a carbureted Cessna 177
 
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GlennAB1 said:
Sorry, not on real airplanes.
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Bet me.. :)

Almost every tank fitting on a Cessna is a pipe thread. and the fuel selector, and carb inlet fittings as well as the brake master cylinder to hose, and hose to brake caliper.

The proper lube for them is "Parker fuel lube", and a tiny bit goes a long ways.
 
bnt83 said:
leads to a $35 million lawsuit when thread sealant plugged a fuel flow sensor and sent an RV10 to the dirt.

http://media.oregonlive.com/pacific-northwest-news/other/experimental.crash.suit.pdf


This isn't the first time and it won't be the last. Pipe threads are all over airplanes and even helicopters and you never know what mechanic/homebuilder X, Y or Z might use on them to seal it.
Click to expand...

What do you want from a home builder, Smarts? a little bit is good? more should be better ??
 
GlennAB1 said:
Sorry, not on real airplanes.
Click to expand...

Glenn, like it or not many participants on this forum build and fly experimental category aircraft. Your background in maintenance and repair of transport category aircraft does not entitle you to pass judgement on the suitability of experimental aircraft for use by others.
 
As sad as a death in any airplane is, I see no reason for this lawsuit, not to mention the many statements relating to certificated airplanes which do not apply.
 
bnt83 said:
Even fuel lube can cause a problem.
Click to expand...

That's why a little bit goes a long ways.

Any numbnuts can have problems with any thing.

say "proper use a thousand times". as penance for your post.
 
I'm thinking more along the lines of a mechanic working a 12 hour shift for $20/hr finishing up installing _____________ fuel system component on ___________ airplane, not finding an accumulation of gunk in a NPT fitting....

There are fittings and methods that don't require a small deposit of a fuel -insoluble compound to seal the joint. Not only that but those joints are also used on the same airplane as the pipe thread type... (the other type is an o-ring and jam nut)
 
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The internet is a series of stupid pipes.
 
Ok, I couldn't read the whole lawsuit stuff. But did I get this right?


[edit]
Airplane runs out of gas, pilot effs up and crashes instead of landing.
Pilot effs up and doesn't look at his watch in addition to the fuel meter causing it to run out of gas.
Somebody effed up and put too much pipe RTV **** on a fitting causing the fuel meter to read wrong. line to get plugged.
It's the fault of the FAA and Vans Aircraft.
 
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N62DN

The pilot, who was also the builder of the experimental kit airplane, departed for a cross-country flight from his home airport. The passenger reported that, following a normal departure, the airplane continued the takeoff climb through some cloud wisps and ascended above a lower cloud cover with an overcast layer above. Suddenly, the engine experienced a total loss of power. The pilot maneuvered the airplane toward the closest airport, but, when he realized that the airplane would not be able to glide to the airport, he attempted to make an off-airport landing. The airplane stalled and then collided with terrain in an open area of a paper mill. Ground scar analysis and wreckage fragmentation revealed that the airplane descended in a steep, near-vertical, nose-down, left-wing-down attitude before it impacted terrain. The pilot installed a fuel flow transducer about 2 to 3 weeks before the accident and used heavy applications of room temperature vulcanization (RTV) silicone to seal the fuel lines. A friend of the pilot, who was also a mechanic, reported that he had observed the pilot about a year earlier using heavy applications of RTV silicone to seal parts during a condition inspection and that he had mentioned to the pilot that this was an improper practice. A bead of RTV silicone was found in the fuel line, and it is likely that it blocked the inlet of the transducer and starved the engine of fuel. Additionally, subsequent to the loss of engine power, the pilot failed to maintain sufficient airspeed while maneuvering to locate a suitable off-airport landing site and flew the airplane beyond its critical angle-of-attack, which resulted in a stall and loss of airplane control.

The National Transportation Safety Board determines the probable cause(s) of this accident as follows:
A total loss of engine power due to fuel starvation because of a blocked fuel line that resulted from the pilot’s improper maintenance practices and the pilot’s subsequent failure to maintain adequate airspeed while attempting a forced landing, which led to the airplane exceeding its critical angle-of-attack and experiencing an aerodynamic stall.
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Sounds a little different than the way some of you guys are imagining it. Stupid slathered on top of incompetent. It's especially awesome how he ignored advice from others and just slathered more RTV all over his joints.
 
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Capt. Geoffrey Thorpe said:
Ok, I couldn't read the whole lawsuit stuff. But did I get this right?

Airplane runs out of gas, pilot effs up and crashes instead of landing.
Pilot effs up and doesn't look at his watch in addition to the fuel meter causing it to run out of gas.
Somebody effed up and put too much pipe **** on a fitting causing the fuel meter to read wrong.
It's the fault of the FAA and Vans Aircraft.
Click to expand...

In this case its alleged that pipe dope (in this case RTV was used) plugged the fuel flow sensor which doesn't contain a bypass, not a fuel quantity problem.


They also accuse Vans assembly instructions to be inadequate, not covering NPT assembly.

Lawyers are blaming everyone except the RTV manufacturer.
 
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ollopa said:
N62DN



Stupid slathered on top of incompetent. It's especially awesome how he ignored advice from others and just slathered more RTV all over his joints.
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They wouldn't want me on that jury. Vans and the other part manufacturer would have a good frivolous lawsuit against these people.
 
I just kinda wish pipe threads went away in aircraft fuel and maybe even hydraulic systems.

Especially on those occasions where you are trying to torque an elbow into a casting, to line up with another fitting.

There's a better way and its been in use for decades.
 
Was it pipe thread or AN fittings? Court document mentions AN fittings, I thought those went together without sealant.. And if you are supposed to use sealant on AN fittings, I guess I'm real lucky with my car's fuel system :eek:
 
FredFenster said:
Was it pipe thread or AN fittings? Court document mentions AN fittings, I thought those went together without sealant.. And if you are supposed to use sealant on AN fittings, I guess I'm real lucky with my car's fuel system :eek:
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AN fittings can have pipe threads.
elbow_zpskqh1mpfi.jpg
 
They can also have straight pipe threads vs tapered pipe threads......
at least we don't have whitworth and BSP to deal with....normally.

Frank
 
ollopa said:
N62DN



Sounds a little different than the way some of you guys are imagining it. Stupid slathered on top of incompetent. It's especially awesome how he ignored advice from others and just slathered more RTV all over his joints.
Click to expand...

So it's not a pipe thread problem but an assembler problem. Sorry he took someone with him. Sometimes just waiting for the Darwin Award is not an satisfactory strategy when disaster is likely...
 
3393RP said:
Glenn, like it or not many participants on this forum build and fly experimental category aircraft. Your background in maintenance and repair of transport category aircraft does not entitle you to pass judgement on the suitability of experimental aircraft for use by others.
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If you fly ultralights you should have thick skin, it was a joke, I'm by far not the first to say it. PS, Sorry, should have warned that it was 2 for 1 day.
 
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1RTK1 said:
They wouldn't want me on that jury. Vans and the other part manufacturer would have a good frivolous lawsuit against these people.
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You are a pilot. You would never be allowed on that jury.
 
Tom-D said:
What do you want from a home builder, Smarts? a little bit is good? more should be better ??
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tom I find that insulting. I know a lot of A&P's that do not not use proper methods also. Most homebuilts have better workmanship than most certified birds.I have seen some really bad stuff in certified aircraft also.

bob
 
Most products at the auto parts stores labeled "RTV" are the silicone type that cure in a reaction with moisture in the air. These sealants are for use in gasket applications and other similar situations, not for pipe joint compounds.

Pipe "sealants" (which is more properly called pipe joint compound) usually contains PTFE and kaolin, clay, vegetable oil, rosin, and other binders. However, there are compounds made specifically for use with fuel and it is without a doubt essential to use the proper compound for the fluid in use.

Tapered pipe threads are made leakproof via a physical mechanism. Tightening the joint reduces the clearance between the threads. The addition of pipe joint compound isn't made to stop leaks.

It is actually a lubricant which reduces the friction between the pipe and the fitting (or the friction between a fitting and a threaded opening in a casting such as an engine block). The pipe joint compound also fills any minute voids between the threads and helps seal the joint, but most of the sealing effect is from the interference fit of the two pieces.

Applying more "sealant" on a joint has little effect in making it less likely to leak. The integrity of the joint is more dependent on properly formed threads.

Many people daub copious amounts of joint compound on a leaky joint in the misguided belief it will stop a leak. Most of the time this is a vain effort because misformed threads are the problem.

In this particular case, it sounds like the assembler did just as I have described, to the point where excess joint compound clogged the pipe and impeded the flow of fuel.

If a the threads on a joint are properly formed, it takes very little joint compound to effect a proper leakproof seal. The amount is certainly less than any amount which flows out of the joint and would need to be wiped off.

Keep this in mind when you are assembling such a system. Make sure the joint compound is specified for use with gasoline, such as Permatex 51H. PTFE tape should not be used for gasoline systems because it can shred and cause blockages.

http://www.permatex.com/documents/TDS/automotive/80045.pdf
 
There but for the grace of...

A few years back Karen and I were flying in the Sky Arrow over a rather desolate part of SE GA. The ROTAX suddenly got VERY rough. Declared an emergency - easier because I keep my radio on 121.5 per NOTAM - and found a field. Maneuvering towards it the engine smoothed out a little, then a lot. Backtracked to the nearest airport and landed. After extensive ground running things seemed fine and we continued on our way, albeit nervously.

When we got home I pulled the float bowls from the BINGs and found this:

21721359813_5b215cc81e_z.jpg


...and this:

22155587009_8d1b32d005.jpg


Long story short, I had been having trouble keeping the float bowl gaskets in place as I maneuvered the float bowls back into position. I had spread a TINY bit of RTV or gasket maker on the gaskets to hold them in place. Apparently when gas hits RTV it turns it into jelly, and if that jelly gets sucked into a main jet at the wrong time it is not a good thing.

Live and learn.

After finding out that RTV and gas don't play well together, I found out that a dab of grease is the ticket to hold gaskets in place. When gas hits the grease it just dissolves to no ill effect.

In any case, we survived. And was reminded yet again of this:

9437357014_17fcef4778.jpg


I have done enough dumb things in the past that I am loathe to call others names or pass judgment when something like this happens.
 
bnt83 said:
leads to a $35 million lawsuit when thread sealant plugged a fuel flow sensor and sent an RV10 to the dirt.

http://media.oregonlive.com/pacific-northwest-news/other/experimental.crash.suit.pdf


This isn't the first time and it won't be the last. Pipe threads are all over airplanes and even helicopters and you never know what mechanic/homebuilder X, Y or Z might use on them to seal it.
Click to expand...

That whole case is based upon who had the deep pocket, just like Cessna, Piper, and any other manufacturer that has any product.

This whole idea is the best insurance any A&P ever had. I'm broke, go look for someone else to blame.
 
Anticept said:
White lithium grease is what you want to use for the carb bowl gaskets for rotax.
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Not a good idea IMHO. Grease makes the gasket and mating surface slick. When the fasteners are tightened, this can cause gasket displacement and leaks.

Better to use a product designed specifically for this application.

Specially formulated for superior fluid resistance, this polyester urethane based gasketing compound withstands extreme temperature changes without hardening. Its non-setting, non-hardening character remains tacky even with rapid changes in temperature, enabling repeated assembly and disassembly of parts.

Suitable as either a gasket maker or dressing, PermaShield™ seals surface imperfections between metal parts and is ideal in high performance applications. With an operating temperature range of -60° to 500°F (-50° to 260°C), this compound resists common engine fluids, including oil, gasoline, ethanol, water and anti-freeze and prevents contamination from moisture and dust.
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http://www.permatex.com/products-2/...sistant-gasket-dressing-flange-sealant-detail
 
I have installed those fuel flow sensors. The instructions that come with them tell you to use NO SEALANT. NONE AT ALL. The body of the thing is zinc, which is rather soft, and the pipe threads will seal just fine if one is careful. Any tiny bit of sealant can stop the rotation of the tiny paddlewheel in it and hinder fuel flow.

RTV is good for weatherstrip and the like. It doesn't belong in the engine or fuel or oil systems. When I was a machine shop foreman in an air compressor and control valve remanufacturing business, RTV was a major cause of early failures of thousands of components, including compressors when the oil feed galleries were plugged by it.

The wedging action of tapered pipe threads also break a lot of components. They usually get way overtorqued and sometimes split the port. Can get expensive.

I usually use a small amount of fuel lube on pipe threads, and nothing at all on the last couple of threads at the end of the fitting. Fuel Lube (now known as EZ-Turn) is a sealant and anti-seize compound, and a handy thing when aluminum fittings are going into aluminum thread ports. Prevents the galling that often happens to such combinations. I have also used the old Aviation Form-A-Gasket. Never teflon tape, but occasionally a maintenance manual will call for the white Loctite teflon pipe sealant compound (Loctite 565 or 567).

Any sealant will leave bits of itself when the fitting is taken out, and a careful mechanic will clean that stuff out before it causes trouble.

As has been mentioned, this sort of thing is way better:

1964.07-Boeing%20727%20Fig%201_0.jpg
 
I found this on another website:

The Van's Aircraft build manual states in section 37, Fuel System, "When installing fluid fittings with pipe threads do not use Teflon tape. Use instead, fuel lube or equivalent pipe thread sealing paste."
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I am not an aircraft builder.

I like to use this stuff to hold gaskets in place during assembly (for cars)
80062.jpg


Works basically like contact cement and it doesn't squish out all over the place like RTV does. Also easier to clean up during disassembly.

Down at the pick 'n pull, RTV is the hallmark of an amateur repair. I've picked up a couple engine cores and it's amazing how often people over-use and excessively apply RTV. It squishes all over into the internal passages, restricting flow and often breaking off and clogging either a coolant passage or the oil pump pickup screen. About the only time I'll let RTV near a gasket now is if the mating surfaces are in really bad shape and have pitting that needs to be filled.
 
Clark1961 said:
So it's not a pipe thread problem but an assembler problem. Sorry he took someone with him. Sometimes just waiting for the Darwin Award is not an satisfactory strategy when disaster is likely...
Click to expand...

It was an assembly problem. Tapered pipe threads still is a crappy design.

Ever tried to assemble a tapered pipe thread elbow into a $1,000 casting and get the outlet lined up with a rigid airframe pipe? Pretty much never reach torque when elbow is clocked correctly because its either over torque or under torque. Over torque = risk of cracking the boss.
 
bnt83 said:
It was an assembly problem. Tapered pipe threads still is a crappy design.

Ever tried to assemble a tapered pipe thread elbow into a $1,000 casting and get the outlet lined up with a rigid airframe pipe? Pretty much never reach torque when elbow is clocked correctly because its either over torque or under torque. Over torque = risk of cracking the boss.
Click to expand...

I've been working with NPT all my adult life...and I'll stand by my position that it was an assembler problem, not an assembly problem. If something is put together wrong then the person that put it together is at fault. Using RTV sealant on NPT connections is wrong. Using so much of any sealant that it clogs things is wrong. Two wrongs don't make a right and in this case it resulted in a loss of power where a third wrong was added to the mix and the result was two deaths and a lawsuit.

As for your problem with lining up an elbow, the old saying is that there exists more than one way to skin a cat.
 
FastEddieB said:
There but for the grace of...

A few years back Karen and I were flying in the Sky Arrow over a rather desolate part of SE GA. The ROTAX suddenly got VERY rough. Declared an emergency - easier because I keep my radio on 121.5 per NOTAM - and found a field. Maneuvering towards it the engine smoothed out a little, then a lot. Backtracked to the nearest airport and landed. After extensive ground running things seemed fine and we continued on our way, albeit nervously.

When we got home I pulled the float bowls from the BINGs and found this:

21721359813_5b215cc81e_z.jpg


...and this:

22155587009_8d1b32d005.jpg


Long story short, I had been having trouble keeping the float bowl gaskets in place as I maneuvered the float bowls back into position. I had spread a TINY bit of RTV or gasket maker on the gaskets to hold them in place. Apparently when gas hits RTV it turns it into jelly, and if that jelly gets sucked into a main jet at the wrong time it is not a good thing.

Live and learn.

After finding out that RTV and gas don't play well together, I found out that a dab of grease is the ticket to hold gaskets in place. When gas hits the grease it just dissolves to no ill effect.

In any case, we survived. And was reminded yet again of this:

9437357014_17fcef4778.jpg


I have done enough dumb things in the past that I am loathe to call others names or pass judgment when something like this happens.
Click to expand...

I had a set of motorcycle carburetors that I couldn't get gaskets (used a molded oring-like thing) for anymore, I wish I had known about aircraft fuel tank sealants then...


http://www.ppgaerospace.com/Products/Sealants/Fuel-Tank-Proven-Standards.aspx
 
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ollopa said:
Down at the pick 'n pull, RTV is the hallmark of an amateur repair. I've picked up a couple engine cores and it's amazing how often people over-use and excessively apply RTV. It squishes all over into the internal passages, restricting flow and often breaking off and clogging either a coolant passage or the oil pump pickup screen.
Click to expand...

My favorite is when someone uses silicone sealant on intake manifold valley end gaskets. Blue Permatex silicone seems to be the weapon of choice.

When the manifold is torqued down (and of course before the sealant is cured) the slick elastomer gasket squirts out like a banana peel, leaving a 3/32" void that leaks copious amounts of oil. The gasket on the rear of the manifold is always the one that leaks because you can't see it.

I normally use a tiny bead of 3M 8001 to adhere the valley gasket to the block and let it cure.

Here's a perfect example of globbing on ten times more sealant than needed...this photo was posted on a forum as an example of how to properly seal the intake. :mad2:

Note there is silicone on the manifold and the block! The block gasket mating surface is filthy...yeah, it's gonna leak.

DSCN9187.jpg
 
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