Flared and Flareless compression tube fittings in hydraulic and fuel lines

[chris ballance]

Did all the major powers in WW2 have their own standard flared and flareless tube fitting standards like the US had AN? Were flared fittings dominant in fuel and hydraulic systems? Was there any degree of interchangeability?

 

[FLYBOYJ]

Did all the major powers in WW2 have their own standard flared and flareless tube fitting standards like the US had AN? Were flared fittings dominant in fuel and hydraulic systems? Was there any degree of interchangeability?

From my understanding the only difference with flared fittings were the degree of the flare (37 and 45 degree). I believe the Germans, Japanese and Soviets used metric sizes and flareless fitting came later if not after WW2 IIRC.

 

[chris ballance]

From my understanding the only difference with flared fittings were the degree of the flare (37 and 45 degree). I believe the Germans, Japanese and Soviets used metric sizes and flareless fitting came later if not after WW2 IIRC.

I was just reading about the founding of the Crawford Fitting Company (Swagelok) in 1947-48, I guess that was the first two ferrule compression fittings. For some reason I thought they were older. Maybe It's because senior engineers I worked under hated them so much when it came to high pressure liquid fuel and gas lines.

 

[FLYBOYJ]

I was just reading about the founding of the Crawford Fitting Company (Swagelok) in 1947-48, I guess that was the first two ferrule compression fittings. For some reason I thought they were older. Maybe It's because senior engineers I worked under hated them so much when it came to high pressure liquid fuel and gas lines.

I never liked them because I always found them difficult to repair in the field. Old fashioned aluminum fluid lines and a flaring kit always worked fine for me.

 

[chris ballance]

My background is in a university lab where nothing had to fly, so everything was mostly stainless. The Air Force guys we sometimes worked under had a low tolerance for leaks, which is good for high pressure hydrogen and oxygen.

 

[Old Wizard]

I used the Swagelok stainless steel fittings on 3000 psi sour gas installations. Had to use a special thread sealant

 

[MIflyer]

A friend of mine who was the 9th PRS maintenance chief said that at the beginning of WWII aircraft typically had unflared tubes that used ferrels and the associated fittings. The first models of the B-17 were that way, for example. Later aircraft had the 37 degree flared tubes and AN fittings, although I am aware of some that made some use of 45 degree automotive type flared tube fittings.

I think the use of Marman type clamps for ducts and liquid tubing was postwar. We used a lot of Marman type clamps for bleed air ducts on the USAF airplanes I worked on in the mid to late 70's.

 

[Snautzer01]

Ok i am stumped by all you guys talking shop. I need some dirty pictures to know what the hell you are talking about plse. Marman type clamps for bleed air ducts why dont you.

 

[FLYBOYJ]

Ok i am stumped by all you guys talking shop. I need some dirty pictures to know what the hell you are talking about plse. Marman type clamps for bleed air ducts why dont you.

 

[Snautzer01]

Well.. i be flared. Thank you FLYBOYJ

 

[MiTasol]

A friend of mine who was the 9th PRS maintenance chief said that at the beginning of WWII aircraft typically had unflared tubes that used ferrels and the associated fittings. The first models of the B-17 were that way, for example. Later aircraft had the 37 degree flared tubes and AN fittings, although I am aware of some that made some use of 45 degree automotive type flared tube fittings.

I think the use of Marman type clamps for ducts and liquid tubing was postwar. We used a lot of Marman type clamps for bleed air ducts on the USAF airplanes I worked on in the mid to late 70's.

As far as I know high pressure plumbing prewar used flared fittings. Prewar fittings were an Air Corps specification and prefixed AC. They had a wider flare than AN and a shorter thread on the various fittings.

Low pressure systems used beaded fittings.

I have no texts handy that show the above joints but when I get home tomorrow I will photograph examples.

 

[chris ballance]

I used the Swagelok stainless steel fittings on 3000 psi sour gas installations. Had to use a special thread sealant

Like everything it depends on the skill of the person making the fitting, but based on my experience if a AN flared connection was made that didn't leak during the first test, the fitting was less likely to leak over it's life and the connection could be taken apart and put together more times than a Swagelok compression fitting (two ferrule, non flared). Not to knock Swagelok guys, I used their fittings on many 1500-2500 psig helium lines at temperatures up 900F. we are talking about being able take a apart connection 6-8 times vs 12-16 and having a much less chance of a leak. I have seen AN fittings used on small liquid rocket engines on test stands with 3000+ psig hot oxygen and RP-2 liquid fuel lines. I believe most of the US Air Force and many aerospace companies moved on from AN to things like beam seal fittings, but I have not used them.

Note, none of fitting connections at high temperature were reused, and many could not even be taken apart.

 

[MIflyer]

TM 1-407, dated 1 Nov 1941 describes flare tube fittings as well as pipe thread fittinsg and uses of hose sections and clamps between tube sections. On my 1946 airplane mostly flare tube fittings are used but originally it used ferrel fittings at the brakes, (which is not a high pressure connection). Given that many pre-war brakes were low pressure rather than high pressure (B-17 as well as Ercoupe) ferrel fittings may have been in use for those applications.

I guess everyone knows what a B-nut is but there is another type of fitting that does much the same thing in a different way. A B-nut uses a sleeve that slides under a nut. The other design, seen much less often, uses a sleeve built into the nut. I wonder if the other design is an A nut, but I have been told that is not the case.

For flare tube fittings one answer to leaks is the use of conical seals to go between the conical surfaces. These are not allowed in space launch applications, for fear they are simply masking a leak rathenr than fixing it.

 

[chris ballance]

TM 1-407, dated 1 Nov 1941 describes flare tube fittings as well as pipe thread fittinsg and uses of hose sections and clamps between tube sections. On my 1946 airplane mostly flare tube fittings are used but originally it used ferrel fittings at the brakes, (which is not a high pressure connection). Given that many pre-war brakes were low pressure rather than high pressure (B-17 as well as Ercoupe) ferrel fittings may have been in use for those applications.

I guess everyone knows what a B-nut is but there is another type of fitting that does much the same thing in a different way. A B-nut uses a sleeve that slides under a nut. The other design, seen much less often, uses a sleeve built into the nut. I wonder if the other design is an A nut, but I have been told that is not the case.

For flare tube fittings one answer to leaks is the use of conical seals to go between the conical surfaces. These are not allowed in space launch applications, for fear they are simply masking a leak rathenr than fixing it.

Yes, I have seen seen those copper seals between the conical surfaces used for ground based stuff. I still know a older technician out at Edwards, need to find an excuse to visit and talk with him before he retires.

 

[MIflyer]

As far as Marman clamps, or V-band clamps, attached is some info. But the dummies who wrote this document STILL did not show how they are used!

Note that Marman clamps are commonly used to attach spacecraft to booster rockets, as well.

 

[cvairwerks]

B-nuts for low pressure lines, beam seal fittings for high pressure stuff, Wiggins clamps for low pressure, but large diameter tubes and ducts, and V-band clamps for low pressure high temp, large diameter tubes and ducts.

The auto guys have gone to V-band clamps on intake and exhaust duct work, while using Wiggins for fuel and coolant lines.

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[manta22]

From my understanding the only difference with flared fittings were the degree of the flare (37 and 45 degree). I believe the Germans, Japanese and Soviets used metric sizes and flareless fitting came later if not after WW2 IIRC.

The standard AN fittings had a 37 degree flare angle; the 45 degree flare fittings were used in automotive and industrial applications. Needless to say, mis-mating the two types will cause problems!

 

[MiTasol]

AC fittings, which preceded AN, fittings used 45 degree flares and were often refered to as Parker fittings and used Parker part numbers. The DC-2 used Parker part numbers so I would expect the other civil aircraft of the period to have done the same.

More detail when I get home later today

Some modern aircraft use flared fittings and others use Ermeto fittings and in airlines it is a customer option. At one stage one DC-9 operator I know made the mistake of buying an additional aircraft from another operator that was same series and subseries but built for a different operator only to discover that, unlike the rest of their fleet, it had Ermeto fittings. That meant every hydraulic component had to be paired to a kit containing Ermeto fittings and all the appropriate seals and the fittings changed before installation. A real pain in the prosterior for the line maintenance staff who were always trying to keep aircraft on schedule.

 

[chris ballance]

Ok, so Ermeto EO fittings were developed in Germany in the early 1930s. Parker bought Ermeto and introduced them to the US. Includes body, a progressive ring (ferrule) and a nut. That's a cool bit of history. Thanks! (figure from Parker Manual for EO & EO2 fittings)

https://www.hydradynellc.com/images...ker/EO_and_EO-2_Metric_Bite_Type_Fittings.pdf

 

[Denys Jones]

This should clarify things

CHAPTER 5

You also need to note that the British used their own system which is generally similar in concept but differs in the threads, angle of the cone etc. It's reference is part of their AGS syste of aircraft hardware.

cheers