hybrid cartridge protoype without burst disk

[jackssmirkingrevenge]

yeah, I got it... I like redheads, don't you remember??

Indeed

I am sure you can do both... you know, I am not talking about the hybrid catridge, right ? : D

hehe not from this distance... but seriously, I'm not happy with fuelling/ignition consistency, there's some more thinking to be done before I make more prototypes. Already planning a vacation in Paris, this is getting dangerously serious...

Any server problem where there's an almost perfect backup available is not a "great collapse"

Fine, I was just being dramatic

[Crna Legija]

on the sentry gun BBMG

I am sure you can do both... you know, I am not talking about the hybrid catridge, right ? : D

while the epoxy is curing on one he can work on the other

i see some hidden message

[POLAND_SPUD]

there's some more thinking to be done before I make more prototypes

Actually it's the other way round - If you are not careful you can make your first successful prototype ever...

Don't forget to use a burst disk rated high enough... techniques that rely on timing are not reliable : D

[jackssmirkingrevenge]

Don't forget to use a burst disk rated high enough... techniques that rely on timing are not reliable : D

In this case, a burst disk would be a tragedy. Another solution, one which I am particularly partial to, is chambering the cartridge in a different breech, in such a manner that if the disk bursts no further prototypes will be created.

Anyway, this going slightly off topic

[Ragnarok]

[POLAND_SPUD]

well I was going to suggest that... but it requires good lubrication of both the breech and the cartridge...
Of course it has some advantages too... tight fit is always a good thing

off topic

have you got the valves you ordered ? I am asking because you can use them to build a metering station for the cartridges (though I don't remember if they had all the 3 ports threaded?)

Oh I have another suggestion... have you considered using flint ignition ?? something along these lines ->

[jackssmirkingrevenge]

have you got the valves you ordered ? I am asking because you can use them to build a metering station for the cartridges (though I don't remember if they had all the 3 ports threaded?)

You mean these?

As in, feed fuel to a set pressure, then flip the valve to feed the air?

well I was going to suggest that... but it requires good lubrication of both the breech and the cartridge...
Of course it has some advantages too... tight fit is always a good thing

I will agree with Rag here that the infamous pink elephant is well and truly rampaging... in that photo it appears to be dousing itself with some sort of flammable liquid in preparation

[POLAND_SPUD]

As in, feed fuel to a set pressure, then flip the valve to feed the air

yeah I would be more useful if it had 3 fully ported threads though. You could use volumetric fueling with that

[jackssmirkingrevenge]

I think decanting from a premixed chamber is the simplest and most reliable option.

You could have say a 2 litre soda bottle, and attach a ball valve with schrader connection, inject the correct amount of propane for say a 5x mix, then pressurise it to 60 psi. It can easily take that pressure, and in the very unlikely event of catastrophic failure shrapnel won't be a problem.

There's an amount of adapters that need to be made, but it would be a one-time job.

[POLAND_SPUD]

It is certainly a viable option. Some would say it's a bit risky and I can understand that but I am sure that the risk can be minimized if you add a burst disk on the tank
(though not the same we were talking about earlier )

[jackssmirkingrevenge]

(though not the same we were talking about earlier )

That has been used in firearm applications before, such as being slipped over the muzzle to protect from sand ingress in desert scenarios

It is risky, but in the scheme of things when it comes to spudguns, I think the risk is minimal, as it's extremely unlikely that you would accidentally generate a big enough spark to ignite the premix tank, unless of coure you're silly enough to click the ignition while the tank is still attached to the cartridge.

Using a bigger tank for the actual mix also negates the pump's dead volume to a much greater degree than filling the cartridge directly.

In the case of my shock pump with say 3mL dead volume and a 10mL cartridge, the pump volume represents 23% of the total volume. With a 2 litre bottle, it goes down to a mere 0.15% so reliable fuelling is practically guaranteed.

[POLAND_SPUD]

personally I'd preffer maleable iron fittings and a FE tank for the chamber (plus a burst disk for safety)... makes more sense IMO

sure it isn't ideal for portable applications but if it's just a filling station then you might as well install; a simple meter on it

[CpTn_lAw]

I had the same problem i was asking JSR about : pump hose volume.
When it accounts for a pretty big part of the total volume, getting the right mix is tricky.
I would however follow POLAND_SPUD on the FE thing.

[SpudFarm]

shrapnel won't be a problem.

No it wont, but the blood pouring out of your ears will..

Not that I doubt your decision but a steel chamber would be much smarter.
Also, if you are filling cartriges you need a rich mix in the premix chamber, perhaps it is getting rich enough to be unigniteable before mixed with the air in the cartrige?

[Ragnarok]

No it won't, but the blood pouring out of your ears will.

I imagine Jack is smart enough to be in possession of ear protection. Problem solved.

you need a rich mix in the premix chamber perhaps it is getting rich enough to be unigniteable before mixed with the air in the cartridge

Seems unlikely. The explosive limits of propane-air mixes are about an order of 2 each way from an ideal mix.

The richness needed is increasingly small as pressures go up (as the air in the cartridge becomes a much smaller fraction of the mix). It might work for fuelling cartridges of 2x or less, but at higher pressures, the mix in the pre-chamber will get closer and closer to a perfect mix.