Bill,
Are you using the actuating gas for anything else on the vehicle? If
not, as long as you're thinking about using a pyro actuator anyway,
might it be simpler to modify the pyro device to generate the volume of
gas you need directly, and delete the cold gas supply? When possible,
simplify. (Though I recognize that there are any number of possible
factors I may not be aware of rendering this simplification impractical.)
Possible off-the-shelf source for such a precision-actuated pyro gas
source might be an auto airbag actuator.
Henry
On 10/25/2020 4:39 PM, William Claybaugh wrote:
Troy:
That’s an ad hoc genius idea.
My concern would be that we have two different burst failure problems: the low pressure side had to fail toward low pressure, the high pressure side has to fight the pressure on the other side of that disc. The charge required for the latter is obviously greater than that required for the former. And in both cases we are venting hot gas into our system....
Bill
On Sun, Oct 25, 2020 at 5:31 PM Troy Prideaux <troy@xxxxxxxxxxxxxxxxxxxxx <mailto:troy@xxxxxxxxxxxxxxxxxxxxx>> wrote:
I helped a guy with PSANCP research for his master’s thesis years
ago. He built a pretty snazzy static testing rig c/w burst discs.
He pretty much standardised on cutting all the discs from Al-Alloy
soda cans whose material specs are apparently all within a pretty
narrow tolerance. Being experimental PSANCPs and being tested a
across a broad spectrum of pressure ranges, the burst discs got to
experience multiple situations of “relieving”. He
tested/characterised them with various seat designs from sharp
edge (sharp shearing of the BD) to large radius that provided more
of a typical burst. The sharp edge seats would obviously fail at
much lower pressures but provide a full open conduit when they did
fail.
Maybe 1 possibility might be use 2 burst discs with the pyro
between them. Arrange the BD seating so there’s a sharp shearing
failure in the direction of the pyro pressure (against the
pressure source) so the failure point is both lower in that
direction, but also provides a full flow when open. This is one of
my ad-hoc/on the fly ideas without much thought put into it, so
add appropriate portions of salt.
Troy
*From:*arocket-bounce@xxxxxxxxxxxxx
<mailto:arocket-bounce@xxxxxxxxxxxxx>
[mailto:arocket-bounce@xxxxxxxxxxxxx
<mailto:arocket-bounce@xxxxxxxxxxxxx>] *On Behalf Of *William
Claybaugh
*Sent:* Sunday, 25 October 2020 8:10 AM
*To:* arocket@xxxxxxxxxxxxx <mailto:arocket@xxxxxxxxxxxxx>
*Subject:* [AR] Re: Burst disc thickness
Steven:
Thanks, that conforms with my thinking.
I’m testing the initiators this next week: two forms of
nitrocellulose (cotton and cord) to get a working unit with an
initial cut on the amount of gas generated, I am assuming the
cord will prove easier as it can be cut to a desired length vs.
the guncotton which will need to be weighed.
I’m having disks made in three thicknesses in accord with the
circular flat plate model and will test each to burst in the valve
assembly once those are finished.
Final testing will then use the initiators to punch through the
disk under pressure...the trick there will be to find an amount of
actuating gas that does the job with one charge working but does
not over pressurize with two charges igniting. (I’m using dual
redundant initiation In accord with standard practice for pyro
actuated devices.)
Bill
On Sat, Oct 24, 2020 at 8:36 AM Steven Berg
<skyshredder9488@xxxxxxxxx <mailto:skyshredder9488@xxxxxxxxx>> wrote:
From my experience in using the flat plate model to design
burst disks in a few actuated systems, we used a circular flat
plate to go into testing. The overall thickness was typically
all that needed to be varied. Adhesives and clamping in the
design were also the other first points of design review.
On Fri, Oct 23, 2020, 2:27 PM William Claybaugh
<wclaybaugh2@xxxxxxxxx <mailto:wclaybaugh2@xxxxxxxxx>> wrote:
Having inhaled deeply of the arcana of burst disc sizing;
I find that the entirety of the available math is about
sizing the plumbing, not about design of the burst disc.
For my current actuated burst disc design I have a 1.5"
diameter disk that is clamped at 1.25" diameter. Operating
conditions are air at (probably something better than) -50
degree F (cold soak on the way to 200 Km) and at an
original 125 psia. Using the standard flat plate model I
get this to be 0.050" thick disc of 6061-T6 providing a
safety factor of 1.43.
If I am going to manufacture my own disk (an assumption
worthy of review), then is it correct to just assume a
circular flat plate for initial design, pending testing?
I will be testing prototype initiators next week; for now
I am using an e-match with a very small bit of
nitrocellulose to generate the pressuring gas. The
nitrocellulose is in both "guncotton" and cord form. I
expect the former will be faster but the latter possibly
easier to control since cord length can be directly measured.
All testing will be at a local energetic materials facility...
Bill