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  #11  
Old 03-02-2021, 07:17 AM
mburch's Avatar
mburch mburch is offline
 
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Quote:
Originally Posted by Aluminum View Post
RV-14A plans call for just such a stack-up
Not just the RV-14... many (most? all?) of the previous models have the same arrangement of fittings in the plans.
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  #12  
Old 03-02-2021, 07:17 AM
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DanH DanH is online now
 
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Quote:
Originally Posted by Aluminum View Post
RV-14A plans call for just such a stack-up, with the little 45deg NPT fitting carrying a vibrating hose attached to a manifold on the firewall.
The two lines cannot disconnect the pump fitting from the pump. The fitting cannot rotate in the pump more than a few degrees at worst.

I wish the same could be said for the B nut on the servo hose, given the rearward-then-outboard loop. The plane of the outboard loop is 90 degrees to the big engine shake motion, crankshaft reaction (sketch attached). Obviously 14's are not falling from the sky, but it would be arguably better if the 90 degree fitting pointed straight up or straight down, or in some direction which allowed tying the hose to the engine without so much unsupported length.

Big Picture? The installation goal is to not rely on "tightness", but rather to arrange the parts so there is no moment which will unscrew them.

Quote:
The other piece of this puzzle that is making me uncomfortable is the big 90deg fitting that goes into the fuel pump, which is a "KB" type not NPT, but it is clocked per plans. I was under the impression that o-ring fuel fittings are supposed to be bottomed out so the o-ring works as designed. Clocking defeats this mechanism in unpredictable ways.
Clocking an o-ring fitting is acceptable. Bottoming is not necessary or even desirable.
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  #13  
Old 03-02-2021, 11:15 AM
scsmith scsmith is offline
 
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Quote:
Originally Posted by Aluminum View Post
...
The other piece of this puzzle that is making me uncomfortable is the big 90deg fitting that goes into the fuel pump, which is a "KB" type not NPT, but it is clocked per plans. I was under the impression that o-ring fuel fittings are supposed to be bottomed out so the o-ring works as designed. Clocking defeats this mechanism in unpredictable ways.
O-ring elbow fittings have a glad nut for the O-ring compression. You install the fitting, orient it however you wish, and then tighten the glad nut, which compresses the O-ring as designed, and also acts as a jam-nut to keep the fitting from turning. But it is not a very positive lock to prevent turning, which is why the elbow is normally oriented downward, so that inertial loads on the attached hose can not cause it to turn.
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  #14  
Old 03-02-2021, 01:00 PM
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Quote:
Originally Posted by scsmith View Post
O-ring elbow fittings have a glad nut for the O-ring compression. You install the fitting, orient it however you wish, and then tighten the glad nut, which compresses the O-ring as designed, and also acts as a jam-nut to keep the fitting from turning. But it is not a very positive lock to prevent turning, which is why the elbow is normally oriented downward, so that inertial loads on the attached hose can not cause it to turn.
It's actually called a "gland nut".
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  #15  
Old 03-02-2021, 02:13 PM
Northernliving Northernliving is offline
 
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[ATTACH]Attachment 8969[/ATTACH]
Quote:
Originally Posted by DanH View Post
I recently viewed some photos taken after a fuel starvation incident, and thought it might be good to pass along a tip for the new guys.

The builders' goal was to access the engine driven fuel pump outlet for a fuel pressure sender. He stacked a 90 degree pump outlet, an automotive aftermarket tee fitting (with female and male ends), and a 90 degree tube end on the hose to the servo.

There are at least two issues here. One, it's a string of fittings with a line leading off at a right angle to the primary thread axis. An offshoot line arranged that way can easily become a lever, providing torque to unscrew one of the connections.

Worse, it appears the servo hose was allowed to contact the engine mount tube, downstream of the tube end, which in addition to the above placed another potential turning moment on the stacked connections.

The combination was all but guaranteed to unscrew one of the fittings eventually, and in fact did so. The subsequent loss of fuel pressure resulted in a forced landing, and yes, it could have caught fire in flight.

There are lots of better ways to skin this cat, but for the new guys, the generally accepted EAB practice is to drill and tap the pump fitting for a straight steel nipple, 1/8" NPT to -3 or -4 flare, which couples to the sender hose. The sender hose cannot unscrew the pump fitting, or the servo hose. The modified fitting is so common that Aircraft Spruce sells them already tapped: https://www.aircraftspruce.com/catal...lickkey=335909

Let's be careful out there.
-
In my new engine install, I'm using the 90* fitting sold by ACS with a gland nut followed by a straight fitting to the fuel servo. The fuel line from the pump to the servo is secured to the engine, only. It's the fitting depicted in the Van's drawings for the -8, but my fitting to the servo is straight unlike the drawing. Van's also calls for a 45* 1/8 NPT -4 for the fuel pressure sender. A 90* fitting to the sender seems to fit my application better and will be pointing opposite the line to the servo straight fitting. Is using a 90* not advisable?
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Last edited by Northernliving : 03-02-2021 at 06:55 PM.
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  #16  
Old 03-02-2021, 02:40 PM
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Brian, that combination of fittings can be applied poorly, or well. If you're not sure, come back with photos after installation, and lots of your peers will take a look, ok?
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  #17  
Old 03-02-2021, 06:31 PM
Northernliving Northernliving is offline
 
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Quote:
Originally Posted by DanH View Post
Brian, that combination of fittings can be applied poorly, or well. If you're not sure, come back with photos after installation, and lots of your peers will take a look, ok?
Thanks. Will take a photo this weekend.
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  #18  
Old 03-02-2021, 07:19 PM
scsmith scsmith is offline
 
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Quote:
Originally Posted by hgerhardt View Post
It's actually called a "gland nut".
Oops, yes, thank you. I seem to be having trouble with my "n" key today. Either that, or some spell checker did an auto-corrupt.
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  #19  
Old 03-03-2021, 04:53 AM
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Bill Boyd Bill Boyd is offline
 
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I think I prefer "glad nut."

One, it's much easier to pronounce distinctly.

Two, you'll be glad the nut is tight. (hat tip to Vic).
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  #20  
Old 03-07-2021, 06:49 AM
Northernliving Northernliving is offline
 
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Attachment 9102
Quote:
Originally Posted by DanH View Post
Brian, that combination of fittings can be applied poorly, or well. If you're not sure, come back with photos after installation, and lots of your peers will take a look, ok?
Dan,

Here are some photos of a test fit using a 45* restricted fitting to the manifold on the firewall with the fuel pressure sensor. I'm using a vertical induction fuel injection servo. I've tried the same with a straight restricted fitting and a 90*, and this one seems to work the best and is also consistent with the Van's plans.

Any thoughts/comments/concerns?

Brian
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