Ed
I have used both Swagelok & 37 deg flares. Remember the sealing surface on
a 37 deg flare is the inclined surface. I use conical seals on all cryo
fittings. Effective way to enhance surface sealing. Remember to clean the
equipment properly if using LOX. Also, make sure the materials you are
using are compatible with LOX.
I've used some fairly old 37 deg flare fittings that didn't leak. These
were small fittings 1/4 & 3/8 in. The trick is making the tube flaring.
Follow the instructions that came with my flaring tool. You can practice
with scrap tubing. Remember, most people in the amateur rocketry ranks use
single flared end. I've never used double flare. Make sure when the tube
is cut, it is a level cut. There a specification for the dimensions of a
properly made tube flare end. I can't find it but I've seen it.
I've used aluminum, copper, brass, steel, & stainless tube with equal
success. The important thing is a properly made tube flare. I buy 37 deg
flare fittings at the local Parker store. I've also bought them from
various online vendors. The Parker Store is a little more expensive but I
willing pay the premium for convenience and the ability to be able to touch
and try different configurations. The guys at the local store are helpful.
Swagelok is very good. Used them for years. When I worked at the Lab at
Wright-Patt, we only used Swagelok. I remember my techs arguing with about
how many times a Swagelok could be opened and reused. If the pressure you
are containing is low (below 200 to 300 psi), you can open and close a
fitting a number of times, 8 to 10 maybe more. If you are running high
pressure (<1000 psi) limit the opening & closings to 3-5. However, that
said, the ultimate test is to connect a fitting and leak check it. We have
a spray bottle with soap and water to check. If there are no bubbles are
pressure, it's good to go. Another issue with Swagelok is the tightening.
Do not over tighten.
Hope this helps,
Rick Wills
Huber Heights, Ohio
-----Original Message-----
From: arocket-bounce@xxxxxxxxxxxxx <arocket-bounce@xxxxxxxxxxxxx> On Behalf
Of Ed Kelleher
Sent: Monday, 4 January, 2021 11:01 AM
To: arocket <arocket@xxxxxxxxxxxxx>
Subject: [AR] Cryo flare fittings, break, remake?
How often can 37 deg flare fittings be disassembled and reassembled?
For example LOX -16 duct to ball valve or TC (thrust chamber)?
Does the male mating surface on the valve or TC wear to the point of not
getting reliable seals?
Are there problems using aluminum tube? with stainless hardware?
What's a good flare reference source?
Swagelok has limited break/make capability.
Ed Kelleher