Recently we've had some excellent conversations about fittings and fuel lines. Darwin made a very good point; never assume all the available components of a type are the same quality. In his case it was steel-braided teflon lines from an unknown manufacturer which didn't perform nearly as well as we're come to expect from top product lines.
Yesterday I received a 90 degree fitting for my engine driven fuel pump from Aircraft Spruce. I've gotten in the habit of carefully examining things. In this case it didn't take much to raise eyebrows:
I drove over to the local Parker outlet and bought a 6-C50X-S for comparison. Here's the Parker on the left and the mystery import on the right:
The fun starts when you look close. The next photos were shot through a 10x magnifier with an ordinary digital camera. Not great photos, but they serve the purpose.
First the straight threads on the import. Note the various tooling marks, peeling plating, pits, and damaged threads:
Same threads on the Parker fitting:
The fatigue strength of a fluid fitting is almost entirely dependent on two things, tensile strength of the material and surface finish. I have no idea about the import fitting's material or manufacturing method. I do know the Parker fitting is forged. As for surface finish, the difference is obvious. Tool marks are stress risers, and failed plating will allow corrosion in service creating even more stress risers.
To be perfectly precise, Aircraft Spruce has not violated any rule or law. The web page listing states the pump fittings are not certified and makes no representation regarding source or manufacturer. Each builder will need to make his own determination of "good enough" for his airplane. Speaking for myself, the import fitting is unacceptable.
The lessons are obvious; avoid assumptions about quality. Regardless of source, do your homework and be careful who you trust. Never install anything without a close look.
Yesterday I received a 90 degree fitting for my engine driven fuel pump from Aircraft Spruce. I've gotten in the habit of carefully examining things. In this case it didn't take much to raise eyebrows:
I drove over to the local Parker outlet and bought a 6-C50X-S for comparison. Here's the Parker on the left and the mystery import on the right:
The fun starts when you look close. The next photos were shot through a 10x magnifier with an ordinary digital camera. Not great photos, but they serve the purpose.
First the straight threads on the import. Note the various tooling marks, peeling plating, pits, and damaged threads:
Same threads on the Parker fitting:
The fatigue strength of a fluid fitting is almost entirely dependent on two things, tensile strength of the material and surface finish. I have no idea about the import fitting's material or manufacturing method. I do know the Parker fitting is forged. As for surface finish, the difference is obvious. Tool marks are stress risers, and failed plating will allow corrosion in service creating even more stress risers.
To be perfectly precise, Aircraft Spruce has not violated any rule or law. The web page listing states the pump fittings are not certified and makes no representation regarding source or manufacturer. Each builder will need to make his own determination of "good enough" for his airplane. Speaking for myself, the import fitting is unacceptable.
The lessons are obvious; avoid assumptions about quality. Regardless of source, do your homework and be careful who you trust. Never install anything without a close look.
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