37 degree fitting compatability - aircraft vs. commercial 2

[SteveKxxx]

Many commercial 37 degree flared tube fittings are available that meet SAE J514 standards and fit SAE J1926-1 straight thread ports. How are these fittings compatible with tube fittings that meet SAE AS4395 and fit AS5202 straight thread ports (for example SAE AS5174, union.) I know that the threads are class 3 on the AS4395 fittings and class 2 on the J514 fittings.
Is there any issue that would prevent using an aircraft fitting in a commercial O-Ring Boss port,(SAE J1926-1)?
Can the commercial fittings be used in an AS5202 port?
How exactly are the JIC commercial fittings compatible / interchangeable with the military / aircraft fittings meeting AS4395?

 

[WKTaylor]

SteveKxxx..

Aerospace fluid fittings and non-aero fluid fittings are way-different beasts and should never be mixed.

In theory fittings with same basic [male/female = A/B] thread and cone angles and interior dimensions assemble together; however aero fluid fittings always list a host of sub-tier specifications controling every tiny aspect of the part: pressure rating, material, machined finish quality, inspection, protective finishes, packaging, qualification, etc.

I can't/won't recommend anyone examine detail parts specs as you asked [to determine if A and B can be physically assembled together], simply because parts made for aerospace [MIL or commercial], when installed in a certified aerospace installation, become part of the airworthieness of that system; and if even one [1] non-spec part is introduced, then that system may become instantly non-airworthy.

NOTE.
In a pinch [out in the middle of NO-WHERE with a war-critical mission to fly], or for a homebuilt acft, I might say 'the rules no-longer apply'... but I know enough 'about the rules to break some rules'... but that has only happened a few times in my career [count on one-hand, 36-years].

NOTE.
This also applies to: the tubing, seals, sleeves, nuts, clamps/brackets, etc.

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true.
o For those who believe, no proof is required; for those who cannot believe, no proof is possible.
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion"]
o Learn the rules like a pro, so you can break them like an artist. [Picasso]

 

[tbuelna]

AS5202 (or MS33649) ports have a slightly different profile at the sealing surface than SAE J1926/1 ports, so the compression of the o-ring is not exactly the same. Attached is a page from the Parker o-ring engineering manual that seems to imply AS4395 fittings can be installed in AS5202 or SAE J1926/1 ports using the same o-ring. But as wktaylor noted, even if it fits, you should never substitute a commercial grade fluid fitting in place of an aircraft spec fluid fitting that is specified by the equipment manufacturer. The two fittings are not manufactured to the same standards.

Best regards,
Terry

 

[SteveKxxx]

Thank you Wil and Terry for your replies.

No, I don't intend to install commercial tube fittings on an aircraft! I'm designing equipment for ground testing and it will never fly. The company I work for builds airborne equipment and our development machine shop has the tools for boring and threading the AS5202 ports but not the J1926-1 (commercial) ports. The J1926-1 port tool costs $600 per tube size. All of the other equipment in the system uses the J1926-1 ports and I would like to keep the fittings, nuts and sleeves the same.

 

[tbuelna]

Even if you are constructing a test rig that will be used for qualification or acceptance testing of flight hardware, you need to be careful about the components you use. Unfortunately, test technicians can often be lazy, and if they need to replace a fitting that interfaces with the test article on an acceptance test fixture, they might grab whatever is handy. If this happens to be a commercial fitting rather than the required aircraft spec fitting and a source inspector happens to catch it, even something this silly can create a huge QA non-conformance problem for your company.

Quality and process control are paramount in the aerospace industry. And one thing that you should not do is allow a situation in your manufacturing facility where tools or hardware that are non-conforming might be used for production hardware. The added cost of using aircraft spec fittings and cutting tools even for your test fixtures is well worth it.

 

[SteveKxxx]

Found an old Parker catalog with the following information:

"4300 Catalog"

"SAE Straight Thread Connector Use in MS33649"

"SAE straight thread connectors, such as Parker F50X, need a special hex chamfer of 35° to a controlled diameter to function properly in MS33649 port. In the past, when MS33649 was more popular, Parker fittings were made with this chamfer. However, this port has been superseded by SAE J1926-1 in industrial applications for over 50 years."

"Since J1926-1 is a superior design, Parker, along with other manufacturers, discourages the use of MS33649 port in non-aircraft applications.
In fact, a chamfer modification requirement for MS33649 will not be in the next printing of the SAE J514 specification, again to discourage the use of this port."

"If you must use this port, you have to request fittings with this special chamfer requirement, which makes them special and more expensive."

MS33649 was cancelled on 17 July 2002 and AS5202 was first released on 1 August 2001. This would imply that the catalog is pre-2002.