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Burst Discs are out of style
Posted: Thu Aug 07, 2008 9:23 am
by HybridRAGE
Ok so I have been working on designing a Hybrid all summer and burst discs just aren't something I want to trust too much. Today I found the golden egg.
http://clarkcooper.com/
I am trying to get a pricing on a HEAT ACTUATED - MANUAL CLOSE valve.
Basically at a given temp the valve auto opens and remains open until manually closed. I am looking to integrate a 1 1/2" one into a golfball launcher. If I can get some more info I will post some more.
Posted: Thu Aug 07, 2008 10:18 am
by daberno123
But will the heat generated from an ignition last long enough to trigger the valve?
Posted: Thu Aug 07, 2008 10:33 am
by jackssmirkingrevenge
daberno123 wrote:But will the heat generated from an ignition last long enough to trigger the valve?
If it has nowhere to go, probably...
Posted: Thu Aug 07, 2008 11:03 am
by HybridRAGE
Yea, the valve has a node that triggers instantaneous release. It has a switch that is actuated electrically kinda like a circuit breaker. So the moment the air temp is over say 150F then it opens. Like I said I am looking into it. My other option is to try and incorporate a piston design I saw earlier... but I like this becuase the valve WILL NOT CLOSE until you physically move the lever to reset it. I just hope this thing doesn't cost mucho moolah...
Also anyone have any idea how to tap threads for smaller holes cut into the side of the tube? I have a feeling that it is going to be waay harder with steel pipe.
For those interested I am Pressurizing this cannon with MAPP and pure O2... soo...
I'm also not very aquainted with burst discs but what would be good to hold down roughly 12 atm...
Theoretically I might die doing this.
Posted: Thu Aug 07, 2008 11:09 am
by HybridRAGE
Edit:
12 ATM is roughly 176ish PSI so this whole thing is definitely steel pipe BTW.
Posted: Thu Aug 07, 2008 11:12 am
by Hotwired
It's going to look like a mechanical Dr. Frankensteins monster
I believe you're meaning a
rotary emergency discharge valve and the bore, compared to the rest of it is pretty titchy. Not too bad nailed to a wall in a factory but lugging that about when the bore is 1 1/2" is a bit much.
If you're set on it it'll be interesting to hear about but I'd personally list an unproven valve like that as too expensive to take a chance on.
By expensive I'm expecting that to be several hundred dollars.
A simple QEV in 1" is well over $100 and this is a much more complex valve in 1.5".
Posted: Thu Aug 07, 2008 11:21 am
by HybridRAGE
Yea the weight I think was around 20lb?? I was going to get one matched to the chamber size (2") because I figured that it would still have a wider bore than my barrel. The other thing I was looking into was a guy who used a piston in his but I haven't got around to asking him how to do it.
It's also not a rotary valve. It's straight through. I also realize this may be pricy and seeing as I am paying for college
this prob ain't gonna be done/completed till winter
Posted: Thu Aug 07, 2008 11:30 am
by jackssmirkingrevenge
For reasons of bulk, expense and complication, I think you're better off with burst disks - works for Larda, should work for everyone
Posted: Thu Aug 07, 2008 11:42 am
by HybridRAGE
Hmm then what's a good recommendation for burst discs to hold up to around 125ish psi?
I just dont want to have to take it apart every time I want to fire it.
Posted: Thu Aug 07, 2008 1:08 pm
by frankrede
Sheetmetal+rubber gasket
edit: And if you don't want to take it apart, then don't build a hybrid.
Posted: Thu Aug 07, 2008 1:12 pm
by jimmy101
HybridRAGE, I suspect that the heat sensing valve won't work the way you expect it to. In a combustion chamber the temperature is very high but there isn't really all that much heat. Heat is not the same as temperature and heat is what triggers the valve.
The sensor will have a fairly high heat capacity compared to the combustion gases. That means it'll heat up pretty slowly. WAG, it'll heat up about as fast as the combustion gases cool down because of heat loss to the chamber wall. By the time the valve cycles you may well have lost most of the energy in the chamber to heat conduction.
It takes so much energy to heat even a small amount of a solid that a tiny little thermocouple can't track the temperature in a combustion chamber. It has too high of a heat capacity (basically thermal inertia) and can't respond anywhere near fast enough.
To get this to work I think you would have to use a valve that triggers at a pretty low temperature, perhaps something like only 100C.
You also have to worry about how fast the valve opens.
Posted: Thu Aug 07, 2008 1:41 pm
by HybridRAGE
frankrede wrote:Sheetmetal+rubber gasket
edit: And if you don't want to take it apart, then don't build a hybrid.
How thick of sheet metal?
I've built combustion and pneumatic so this is the next step
jimmy101 wrote:To get this to work I think you would have to use a valve that triggers at a pretty low temperature, perhaps something like only 100C.
I thought the same thing about how fast it will register on the sensor. The good thing is that I can get one that actuates at 135F. I'm pretty sure the valve release is fairly quick because it's an emergency release valve.
Alas, it seems perhaps I thought not long enough. Maybe I will try a piston?
Posted: Thu Aug 07, 2008 2:04 pm
by Necrosis
frankrede wrote:Sheetmetal+rubber gasket
edit: And if you don't want to take it apart, then don't build a hybrid.
or use a piston. :/
Posted: Thu Aug 07, 2008 2:20 pm
by frankrede
HybridRAGE wrote:frankrede wrote:Sheetmetal+rubber gasket
edit: And if you don't want to take it apart, then don't build a hybrid.
How thick of sheet metal?
I've built combustion and pneumatic so this is the next step
jimmy101 wrote:To get this to work I think you would have to use a valve that triggers at a pretty low temperature, perhaps something like only 100C.
very thin:)
I thought the same thing about how fast it will register on the sensor. The good thing is that I can get one that actuates at 135F. I'm pretty sure the valve release is fairly quick because it's an emergency release valve.
Alas, it seems perhaps I thought not long enough. Maybe I will try a piston?
Posted: Thu Aug 07, 2008 4:49 pm
by SpudFarm
put it this way, a 64 layered aluminium foil disk over a 2" area has a burst pressure of around 1000psi.
