I kinda hate Swagelok fittings over 3/4". They just suck to get leak
tight. 1/4" and 1/8" swagelok fittings are great, they are perfectly
suited to the task. Work fine with LOX. Follow the assembly
instructions! Buy a preswaging die if you use them a lot. 1/4"
swagelok fittings are the easiest way to build weird assemblies like
temperature/pressure ports in pipes or coaxial heat exchangers. And
work well for things like gauge boxes, test benches, etc. They're also
called "instrumentation fittings" and that is a good description of
what they are good for.
They are not great with vibe. Well suited to ground equipment, less so
to flight.
If you use them with peroxide the nuts should be processed in acid
first. There is silver plating on the threads to act as antiseize, if
you have a peroxide leak through a silver fitting then the fitting
ends up getting hot and the leak escalates itself to asking to speak
to the manager. Once you strip the silver antiseize off, then you need
to replace it with something else on assembly, like krytox.
Any use of any swage fitting over 3000 psi is a mistake. Go straight
from AN to cone and thread. Do not believe the marketing around medium
pressure swage fittings. When a 5000 psi fitting decides to dissociate
next to you, the best case is a startling.
Ben
On Fri, Mar 27, 2020 at 5:05 PM Rick Wills <willsrw@xxxxxxxxx> wrote:
Hi
Has anyone on the list used Swagelok compression fittings in service with LOX
(3/4 or 1 in)? I’ve used AN (37 deg flare) and NPT fittings successfully for
LOX. NPT fittings are wrapped with PTFE tape. My entire LOX side on my test
stand is all AN expect for the NPT adapters used on the main LOX valve and
LOX load valve. Any LOX experience with any other brand of compression
fittings (Parker, etc). I’m looking at changing the stand plumbing and am
considering Swagelok. Check out our Facebook page
https://www.facebook.com/midwestpropulsiongroup to see the stand in action.
The Army missile spec forbids NPT fittings. Most likely reason is they could
vibrate loose. I’ve seem amateur liquid systems using NPT fittings
successfully. Any advice would be appreciated. On my first test stand, I
welded the NPT fittings together. It worked but looked pretty bad. An A&P I
know suggested safety wiring the NPTs so they would come loose. That is a
lot of work.
I’m lucky. My outbuilding is also my rocket workshop. When I want to escape
I run out back for a few hours. Thanks and everyone take care.
Be Safe,
Rick Wills
Huber Heights, Ohio