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  #1  
Old 04-27-2011, 01:58 PM
LettersFromFlyoverCountry's Avatar
LettersFromFlyoverCountry LettersFromFlyoverCountry is offline
 
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Default Silverhawk fittings

Quick question: I need to change the 90 degree fitting coming out of the Silverhawk fuel servo to a straight fitting. Are these standard fittings?
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Bob Collins
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  #2  
Old 04-27-2011, 02:52 PM
TS Flightlines TS Flightlines is offline
 
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Smile O'ring-6 fitting

Bob---they are -6 flare (AN) to o'ring fittings.
How's it coming?
Tom
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  #3  
Old 04-27-2011, 02:54 PM
Lars Lars is offline
 
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Location: Davis, CA
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Default

Quote:
Originally Posted by Bob Collins View Post
Quick question: I need to change the 90 degree fitting coming out of the Silverhawk fuel servo to a straight fitting. Are these standard fittings?
They are, but not what you might expect, at least that was the case on mine. There was a 90? installed on the back, for the outlet. When I removed it, it turned out to be a stainless steel AN833 bulkhead elbow with locknut, but with an o-ring under the locknut to seal it. I was expecting the end screwed into the servo to be what in the hydraulics world we would call an SAE o-ring boss fitting.

There is no AN spec that I could find for an o-ring boss fitting (the threads are the same size as AN/JIC for a given tube size); I wound up getting a US-made Parker stainless steel o-ring boss x -6JIC fitting for mine, from a local hydraulics supplier. JIC and AN are nominally the same, but the thread spec on JIC is looser and in principle means less fatigue life and lower pressure capability. More of a concern with aluminum than steel. I qualitatively compared the AN fitting I removed with the JIC fitting I installed under 10x magnification. I couldn't see a difference. I was looking for cut vs. rolled threads, since JIC allows the former but AN doesn't. It appeared to me that the Parker JIC fitting I inspected had rolled threads. Hardly definitive, but I feel comfortable using the fitting, especially since the fuel pressure is only a few psi at the servo outlet.

For what it's worth, I use those fittings routinely on a large high-g (in excess of 75g) hydraulic shaker with oil pressures around 4000 psi. Never had a fitting fail, though aluminum is verboten on our machine.

If you are interested, the Parker part number is 4 F5OX-SS. Be advised that the supplied o-ring is nitrile; as such it may have trouble with alcohol-laced fuel. If that's a concern, I have the correct size viton o-rings that solve the problem. I have way more than I could ever use, so I can send you one if you'd like.
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  #4  
Old 04-27-2011, 03:07 PM
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LettersFromFlyoverCountry LettersFromFlyoverCountry is offline
 
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Default

Quote:
Originally Posted by TS Flightlines View Post
Bob---they are -6 flare (AN) to o'ring fittings.
How's it coming?
Tom
Slow, but forward. If I can get some of the Minnesota types to stop by sometimes and help me plot an appropriate fuel line route, I'll be needing another fuel line.

I also have to can my stock oil lines and get them shorter (buying Van's stock hoses was a huge waste of money).

Can you refer me to a supplier for the Silverhawk-appropriate fitting? I don't kow the difference between a regular fitting and a fitting-to-o-ring.
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  #5  
Old 04-27-2011, 03:18 PM
Lars Lars is offline
 
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Default

Here's a crappy iPhone pic of the exact fitting. Just looked, lo & behold I have another one.



I'll never need it, and if I do, I can get lots more. Want it?
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  #6  
Old 04-27-2011, 03:53 PM
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Default

That'd be swell. Email me the $ to bcollinsrv7a@comcast.net and I'll shoot you a check.

Bob
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Bob Collins
St. Paul, MN.
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  #7  
Old 04-27-2011, 05:31 PM
TS Flightlines TS Flightlines is offline
 
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Talking bob--

I sent you an email--
Tom
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  #8  
Old 04-28-2011, 06:43 AM
Don at Airflow Don at Airflow is offline
 
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Default Use the correct fitting

What you?re looking for is a fitting for the metered fuel outlet fitting (I believe).
DO NOT use the hydraulic fitting shown in the picture above. While it may work, the hex does not correctly trap the O-ring in the boss. If you cannot find an AN815-4 fitting give me a call and I will send you one. It?s surprising that Precision does not tell you guys what is the proper fittings to use in their servos, especially for the fuel pressure fitting on the servo. We have gotten some of these servos back from customers for repair and the fuel pressure fitting has been run into the inlet screen destroying it. But hey it?s only a $200.00 part to replace!!!!!!!


Don
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  #9  
Old 04-28-2011, 09:01 AM
Lars Lars is offline
 
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Default

Quote:
Originally Posted by Don at Airflow View Post
What you?re looking for is a fitting for the metered fuel outlet fitting (I believe).
DO NOT use the hydraulic fitting shown in the picture above. While it may work, the hex does not correctly trap the O-ring in the boss. If you cannot find an AN815-4 fitting give me a call and I will send you one. It?s surprising that Precision does not tell you guys what is the proper fittings to use in their servos, especially for the fuel pressure fitting on the servo. We have gotten some of these servos back from customers for repair and the fuel pressure fitting has been run into the inlet screen destroying it. But hey it?s only a $200.00 part to replace!!!!!!!


Don
So I'm learning something here myself. Reading between the lines, in aviation applications, it appears that there is no such thing as an o-ring boss fitting as used in hydraulics. Instead, bulkhead or union fittings such as an AN815 or AN833 are used, with the addition of an o-ring. Is that correct? Do you know where I could find the spec for the spotface and chamfer that create the o-ring seat? Presumably it's different than MS16142/SAE J514 if the hydraulic fitting I photographed won't capture the o-ring.

I just want to understand this better. I searched everywhere I could think of, including AC43.13, and couldn't find anything on the subject of o-ring boss style fittings as used in aviation, back when I needed a straight fitting myself.

I'll gladly swap out the one I have myself for an AN815 if it's a safety issue; I probably have one. What seemed weird to me when I wanted a straight fitting was the the 90 degree fitting I removed was an AN833 with the long (bulkhead) end screwed into the servo. There was a nut on the fitting to capture the o-ring and allow positioning of the fitting. It just seemed strange that they would do it that way instead of using an o-ring boss fitting designed for that purpose.
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  #10  
Old 04-28-2011, 10:09 AM
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LettersFromFlyoverCountry LettersFromFlyoverCountry is offline
 
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Default

OK, let's make sure I have this right. What I want is this? And I should slap an O-ring on it?
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Bob Collins
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Blog: Letters From Flyover Country
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Last article: "Gonna Finish This Sucker" (Kitplanes)
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