KB-090-T

YellowJacket RV9 · #1 03-30-2016, 09:07 PM

Hi all,

I have posted about this before, but have never been completely satisfied that I understood, and I am getting very close to first flight, and so would like to understand everything, especially FWF, 100%.

The KB-090-T fitting connects to the output of the engine driven fuel pump. A picture is here: http://www.aircraftspruce.com/catalo...tting00782.php

From previous threads on the topic, Vans and others suggest to install this to the correct orientation, and then tighten down the jamb nut to compress the o-ring. Here's the thing - the jamb nut just turns against a steel flange that is fixed in place on the KB-090-T fitting. It does not compress the o-ring at all. It simply bottoms out on the flange. If I want to compress the o-ring further I need to turn the entire fitting, thus getting it out of the correct orientation. In fact, I don't even see the purpose of tightening the jamb nut, it does nothing. If it turned against a washer or something else moveable, now that would make sense. But a fixed flange that doesn't move or compress makes no sense to me.

As it is now, the fitting in my installation will turn several degrees back and forth with just a tug of the fuel line attached to it. I have run the engine and pressure tested everything with the boost pump on, and there are no leaks, but a fitting that loose doesn't seem right, and I would have to tighten it another full turn to keep it in the proper orientation, which I think would be way too tight on the o-ring, if it would even go that far.

There is no potential for this fitting to back out more than a couple degrees due to the two fuel lines attached to it, but that fact that it wiggles at all concerns me. Should I try to get another full turn out of it? How thin can I crush that o-ring? Or is the slight play normal?

There is something very simple my feeble mind is missing here...

Chris

BillL · #2 03-31-2016, 05:53 AM

In order for that fitting to seal, the o-ring requires an inner smooth and outer smooth diameter. Look at the housing, it should have a relief groove for that o-ring. Then back the jamb nut to the top of the o-ring groove (there the threads are cut off) , thread the fitting into position -hold - tighten the jam nut. This compresses the o-ring to seal.

NO NOT LEAVE THE FITTING LOOSE!! I will leak, then vibration will wallow the threads in the housing and it will leak more.

Something does not sound right about that fitting - the jamb nut should turn free in your hand, then screw down to jam and tighten that o-ring. Can you take it off and get a picture of the housing and fitting to post?

The o-ring should fit in that groove where the threads are missing. The washer should be hard against the housing, and the o-ring should not be "compressed" beyond that.

Walt · #3 03-31-2016, 06:07 AM

The 'O' ring rests in the relief slot of the fitting, screw the fitting in until it contacts the O ring, orient correctly, then tighten the jam nut securely against the pump. As Bill said: DO NOT LEAVE THE FITTING LOOSE OR YOU WILL HAVE A FUEL LEAK !!!!!!!!!

(picture shamelessly stolen from the internet)

YellowJacket RV9 · #4 03-31-2016, 08:01 AM

Thanks guys, I knew something didn't seem right and I don't want to mess around with fuel over my exhaust.

Should that washer move at all? Mine does not move at all, it is just fused to the fitting so doesnt compress against the o-ring when tightening the nut. Mine is also steel when your pictures look like brass.

I am headed to the hangar and will play with it and post pictures if needed.

Update, found the problem Okay, I knew something wasn't right. I pulled the fitting and found that the washer was indeed frozen to the fitting. I was able to work it back and forth in the vise to free it up, but even then it spun but did not want to travel freely up or down the shaft. Some lube and working back and forth has it working better, but now that I know what it SHOULD do, I am just ordering a new one from ACS that hopefully will be smoother. Looking back, I should have realized this problem right away, but having never seen this type of fitting before, I didn't know what I didn't know. This fitting was part of Vans FWF kit, and I would suggest that anybody else who comes to this point make sure that theirs is functioning properly. It's an important area.

Thank you to those that took the time to explain to me what probably seemed very simple to them!

Chris

rightrudder · #5 03-31-2016, 12:01 PM

I'm glad you're getting it resolved, Chris. Never hesitate to ask a seemingly obvious question....I've asked a lot of them here myself, and many were for verification when I was 98% sure what I was doing was correct, yet a niggling doubt persisted. Sometimes it's the 2% that gets ya!

Exciting to hear that you're 99% done. We expect a full flight report.