Fittings are a topic where everyone has their favorite and the cherry
picking data to suit individual preferences are rampant.
- Flare fittings absolutely blow off under high pressure if the flare is
not properly formed (undersized), no different than swagelok/yorlok. Flare
fittings are less tolerant of tube misalignment as well.
- Any fitting cleaned for oxygen service requires a lubricant to prevent
thread galling. Swagelok happen to have the lubricant built in.
- There are hundreds of manufacturers of cryogenic components with NPT
fittings.
- every single commercial Liquid oxygen system has both NPT and
swagelok/yorlok fittings on it.
Examples of old wives tales about fittings:
"xyz fitting is harder to clean" - they all have to be cleaned properly,
i've never seen a fitting that was any harder to clean than any other.
"NPT fittings cant be used above XYZ pressure" - NPT can be used up to
10,000 psi at least with the correct fittings and installation procedures
"Swagelok are likely to blowoff" - this is only true if the human
installing them didn't read the instructions or swaged them incorrectly.
Incorrect installation will cause failure of any fitting.
"XYZ fitting is more or less vibe tolerant" - its likely that not fittings
are equally vibe tolerant. But the idea that this matters significantly
is silly, an I've never seen a reference which actually measured vibe
tolerance of fittings. a 1/4" tube nut is the same dimensions and thread
for Swagelok and AN. I've seen both NPT and tube fittings auto-rotate off
in vibe environments.
"XYZ fitting can be damaged if over tightened" - again this is true of all
options, and isn't a valid argument for or against any one type.
"XYZ fitting isn't used in flight applications" - i'm confident all of
the options discussed here have flown on flight vehicles
For an amateur, on a limited budget, who is unlikely to see anything higher
pressure than a 2000 psi gas bottle, the choice is pretty clear - use
whatever you can get.
To answer the OP's question - Yes I've used 1" Swagelok in liquid oxygen
service.
On Mar 29, 2020, at 10:15 PM, roxanna Mason <rocketmaster.ken@xxxxxxxxx>
wrote:
For those just getting started or who have little/no Swage inventory just
forget Swageloks and base your plumbing on 37 degree flare fittings,i.e.
AN, (Army/Navy). Swage also have trapped areas that are hard to clean even
though not wetted they will be wetted when a leak occurs and if you try to
tighten it when leaking it could explode.
NPT can be used with LOx/cryo but special care has to be taken
especially stainless steel which will gaul with little/no effort.
Teflon tape with grease, LOx compatible like Krytox or Flurolube, an
absolute must. In certain cases pipe fittings are preferred over AN.
This is a complicated topic requiring much time to do justice so of list
discussion is highly recommended, hard to summarize a half century of
experience in a few paragraphs.
Ken
On Sat, Mar 28, 2020 at 8:35 PM Michael Clive <zeinin@xxxxxxxxx> wrote:
To continue on Ben's vibe:
Swagelok is the best brand for compression type fittings. Parker etc are
slightly worse in terms of quality control, from my experience. Surface
finishes are not as nice, plating is worse. Swagelok also is expensive but
very responsive and kind. Their sales reps will do *anything *for you, if
you buy enough. If not, Ebay will get you everything you need.
NEVER mix and match a parker fitting to a swage body, or a parker body to
a swage fitting. They claim they are interchangeable, but they can have
minor variations in geometry and thread form that can gall stuff up or
generally make your day worse.
McMaster compression fittings are Parkers. They are okay, but nothing
beats the real thing.
Swages above 3/4" become a huge pain in the ass and you need a hydraulic
preswaging tool and a second bank account for fittings at or above 1".
Swages are excellent, but you need to be really experienced with them.
There are no torque specs. *there are no torque specs. *You torque them
down until a certain displacement is met. You then always reseat them with
the tiniest bit more oomf. If you don't have a calibrated arm, you will
overswage if you ever reinstall, and it will leak, and you will have to
pull the tube and replace it. There is no spec for this, it's just a
feeling you develop after doing a few hundred of them.
Big super obvious one that bit me when I was green: Don't swage a brass
fitting on a stainless tube, or a stainless fitting on an inco tube. You
can swage stainless on brass or inco on stainless, but always move down the
strength chain. Why? The brass just won't bite the steel tube and it will
'splode. I had it happen on a 1/2" air line and it was loud and very
embarrassing.
And yeah, if you are a rocket person on this list and are working at
20ksi, good job on gettiing your phase 3 in-space propulsion contract from
$GOVBUCKS. Looking forward to your launch.
My post-apocalypse profession is going to be as a plumber.
On Sat, Mar 28, 2020 at 5:34 PM Ben Brockert <wikkit@xxxxxxxxx> wrote:
Ok, I'll backtrack to say that for 1/4" and smaller, higher pressures
are likely to be fine *if* you are swaging correctly and using normal
hardness tubing. The forces are not as crazy. But still, the advantage
of "cone and thread" and AN fittings is that if they are not tightened
they just leak, rather than having the tube go shooting out of the
fitting like an un- or under-swaged tube.
The Swagelok FK medium pressure system in half inch and larger with
thicker and harder tubing is trouble waiting to happen. I've seen it
go off twice, it's very violent and loud. Fortunately in neither case
was anyone injured.
And for folks new to this, "medium pressure" and "high pressure" are
terms of art for specific fitting systems, where medium is up to
20,000 psi and high is up to 60,000. Most rocketeers will never get
into medium pressure, and the highest you'll ever see is a 6000 psi
bottle that can be worked with using normal AN fittings.
And "Swagelok" is a company and a brand, but generally people use it
specifically to mean two ferrule compression fittings in the
Swagelok/Yor-Lok/A-lok line.
On Sat, Mar 28, 2020 at 2:55 PM Michael Clive <zeinin@xxxxxxxxx> wrote:
right (cone-and-thread fittings), they never, ever leak. And they are very
However, to follow up with Ben:
Medium, high pressure and UHP fittings are PHENOMENAL. If you do them
repeatable. Not good for vibe, but for test stands, they are great!
Maximator makes the best tools for them. Peter Duffy at High Pressure
Technologies is about the best sales guy you will ever talk to, and he will
sell you anything you need for 10k+ work. Tubes, fittings, valves, anything.
I agree with Ben on not using bite type fittings EVER for above 10kwork. Cone on thread is the best!
with LOX (3/4 or 1 in)? I’ve used AN (37 deg flare) and NPT fittings
On Fri, Mar 27, 2020 at 8:55 PM Ben Brockert <wikkit@xxxxxxxxx> wrote:
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
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.
they could vibrate loose. I’ve seem amateur liquid systems using NPT
The Army missile spec forbids NPT fittings. Most likely reason is
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.
to escape I run out back for a few hours. Thanks and everyone take care.
I’m lucky. My outbuilding is also my rocket workshop. When I want
Be Safe,
Rick Wills
Huber Heights, Ohio