Aircraft Spruce - A Fitting Drama

[pvalovich]

I'm installing a Matco parking brake valve in my -8A. To redo the brake plumbing, I ordered AN816-4-4D Nipples, AN822-4-4D Elbows, and Weatherhead 3400X4 brass elbow fitting from ACS - expecting to get 1/4" material. The invoice swhows that's what was ordered.

I thought I was getting 1/4" pipe threads on all. However, in all cases, what I received were fittings with a 1/4" flare end, but the pipe ends were all 3/8". For the Weatherhead both the hole and the male end were 3/8".

ACS customer service has been responsive, but we're trying to figure out what happened.

Do any of the viewers have words of wisdom concerning AN/Weatherhead fittings? Did I order the wrong stuff? What are the odds that all 3 fitting types were pulled incorrectly from the ACS bins?

So much for completing the parking brake valve this weekend.

[Radomir]

You sure those are 1/4" pipe threads on the parking brake valve? I thought they were 1/8" pipe thread.. but I could be wrong.

EDIT: http://matco.elixirlabs.com/users/ma...ages/IM27a.jpg

They are 1/8" NPT... so I'm afraid you ordered wrong part...


PS.. I don't remember seeing 3/8" pipe thread ever..could be wrong about that too almost sounds like you're trying to measure diameter... doesnt' work quite that way on pipe threads..

[Sparky]

I think you just ordered the wrong fittings. An AN816-4-4D is a -4 TO 1/4 NPT fitting. What you need is the AN816-4D, which is a -4 TO 1/8 NPT fitting. I did the same thing with a couple of AN fittings awhile ago.

[pvalovich]

I must have been asleep during the NPT lecture - I thought it was the outside diameter that was measured.

"Life is hard, but it's a lot harder when you're stupid" - J. Wayne, Sands of Iwo Jima

But ****, wouldn't one associate -4 with 1/4" stuff?

[John Clark]

A note from the Engineering Tool Box website:

Note! Pipe sizes do not refer to any physical dimensions. The outside diameter of a pipe or fitting must be measured and compared to a table for size identification. A 3/4" NPT pipe thread has an outside diameter - OD - of 1.050 inches.
Each thread size has a defined number of threads per inch - TPI, or pitch. The 3/4" NPT pipe thread has 14 threads per inch. Both the TPI and OD of the thread are required for positive identification of thread size because more than one size have the same TPI.

The whole story:
http://www.engineeringtoolbox.com/np...ads-d_750.html

John Clark
RV8 N18U "Sunshine"
KSBA

[RVbySDI]

Originally Posted by pvalovich

I must have been asleep during the NPT lecture - I thought it was the outside diameter that was measured.

"Life is hard, but it's a lot harder when you're stupid" - J. Wayne, Sands of Iwo Jima

But ****, wouldn't one associate -4 with 1/4" stuff?

I like your quote from J. Wayne.

As far as the -4 standard nomenclature, I have found whatever the standards are in the engineering world for naming things, often they make little common sense to the uneducated such as myself when trying to figure them out. Thank goodness I have a retired machinist buddy to straighten me out on such things.

It should be a prerequisite for new builders that they befriend a machinist, tool and die man, or engineer and add them to their list of tools needed prior to starting their building process.

[airguy]

I had a similar situation a while back, and if memory serves they call 1/4" NPT a -3, not a -4.

[Bob Axsom]

Aircraft Spruce has never done me wrong on fittings. When you are doing plumbing of any of your systems be sure to read the component requirements with respect to the tapered NPT "pipe thread" sizes and the flared fitting "tube sizes". Sometimes you have to get creative with sizes, styles, and combinations but I never came up with any requirement that I could not resolve with the collection of fittings in the catalog and I never had an incorrect fitting delivered in 12 years of building and modifying our RV-6A.

Bob Axsom