Bill,Any way a hot gas valve would work in your application? I'm thinking
along the lines of using a pressure regulator in the place of a burst disc.
You would be able to set the desired pressure, hook the nitrocellulose
cartridge to the input of the regulator, when the input pressure exceeded the
set pressure you would have gas available to do your work. Might not need more
than a simple regulator if only a one shot device is necessary. Just a
thought. Sorry if I have wasted your time. Barry Sent from my Sprint Tablet.
-------- Original message --------From: Kevin Ho <rebelwithoutajob@xxxxxxxxxxx>
Date: 10/26/20 16:56 (GMT-05:00) To: arocket@xxxxxxxxxxxxx Subject: [AR] Re:
Burst disc thickness The benefit of a striker or hammer design vs direct
pressure by the actuator is significantly greater pressure at the point of
impact (thus reliabiity) and a much smaller actuator and battery. The cost is
some greater complexity.If you want to generate a puncture pressure with an
actuator, you need an actuator that can deliver that pressure, which may be
reasonably large.The lighter solution is for a much smaller actuator to push
back and then release a spring loaded mass, which then falls forward and
strikes/punctures the CO2 cylinder. Now you get the benefit of all the energy
stored during the entire stroke of the actuator.A further benefit is the
ability to easily add a mechanical safety, like a transfer bar. You can use the
motion of the actuator to raise a transfer bar, so that unless the actuator is
stroked, the hammer/striker hits nothing but air. That would prevent
inadvertent separation.https://www.youtube.com/watch?v=S9ixC34PaKkThe ;
equivalent rocket system is obviously much simpler, as it only has to go bang
once.On Oct 25, 2020, at 10:40 PM, Troy Prideaux <troy@xxxxxxxxxxxxxxxxxxxxx>
wrote:I’m not familiar with what mechanical systems there are out there. Of
course that would be a preferred solution to pyro *if* there wasn’t too much
mass/volume penalty to drive the puncture. Typically (for HPR separation
systems) all-mechanical puncture systems have been developed (maybe based on
aircraft lifejacket inflation systems?), but rely on clever design to achieve
the required force to achieve the required puncture orifice area for *that*
application. Apparently the force required to puncture out a 0.09” hole in a
16g CO2 canister is about 100lbs – remember the sealing diaphragm needs to be
strong enough to hold… well… probably upwards of 1200psi for really hot
conditions. Now, I did emphasize “that” application which requires a fair bit
of throughput capacity as it’s both acting on a large volume and needs to
compensate (to some degrees) for leakage within the mating pieces, vent holes
and whatever else. Bill’s application, on the other hand, is likely
specifically driving pistons with much more confined volumes and can probably
expect no leakage to compensate for, which does allow a much smaller
orifice/puncture as driving pressure is probably more important than pneumatic
power. Troy From: arocket-bounce@xxxxxxxxxxxxx
[mailto:arocket-bounce@xxxxxxxxxxxxx] On Behalf Of Kevin HoSent: Monday, 26 ;
October 2020 2:59 PMTo: arocket@freelists.orgSubject: [AR] Re: Burst disc
thickness Depending on the altitude/pressure the system is working at, it may
be worth skipping the pyro altogether and using mechanical striker on a spring,
similar to a Glock. It doesn’t take that much force to puncture a CO2
cartridge, and you may be able to use actual Glock parts for it, which are
cheap as dirt and commonly available. It’s mechanically well-trodden ground,
and one great thing about it is making a drop-safe hammer/trigger system is
well known, and that can prevent an accidental discharge.On Oct 25, 2020, at
8:22 PM, Troy Prideaux <troy@xxxxxxxxxxxxxxxxxxxxx> wrote: How about piercing
something like a 12 or 16g CO2 cartridge for your pneumatic drive? You can
actuate that via pyro that’s completely isolated via a driving piston? Use a
suitable spring or compressible/breakable standoff to inhibit premature
piercing. Yes, your flow rate is limited through the pierced orifice, but
(provided it’s pyro actuated) the HPR vendors supplying CO2 recovery devices
use this technique to substitute pyros for complete rocket separation for quite
sizable (in some instances) rockets. Troy Troy From:
arocket-bounce@xxxxxxxxxxxxx [mailto:arocket-bounce@xxxxxxxxxxxxx] On Behalf Of
William ClaybaughSent: Monday, 26 October 2020 12:13 PMTo:
arocket@freelists.orgSubject: [AR] Re: Burst disc thickness Henry: The
pressurized air actuates four pistons that bind the payload to the rocket;
those pistons have to be released by releasing the pressure in order to
separate the payload. It is in principle possible to have a closed pressure
system with a burst disk that is actuated by a pyro charge over pressuring a
“calibrated” burst disk. That is simpler than using a plunger to break the
disk but means that the whole system will be contaminated by the residuals; it
also means that venting will have to be overboard to avoid contamination of the
internal volume of the payload compartment. Finally, redundant charges are
required to assure operation which exacerbates all the above issues. I am thus
inclined to separate the hot actuating gas from the pressurizing system. Bill
On Sun, Oct 25, 2020 at 6:30 PM Henry Vanderbilt <hvanderbilt@xxxxxxxxxxxxxx>
wrote: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.HenryOn 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> 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] On Behalf Of William ClaybaughSent:
Sunday, 25 October 2020 8:10 AMTo: arocket@freelists.orgSubject: [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> 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> 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