Air Cartridge Design

[DarwinsLaw]

Hi all, I realize there have been many posts about air cartridges and I hope I am posting this in the correct section.  I just wanted some opinions on my design. 

[Gippeto]

Is the drawing complete or have you left out details that might clarify the operation cycle?

I presume the spool_striker is to be hit by a firing pin of some sort, but then what? How do you see the valve opening?

Al

[DarwinsLaw]

Yes the striker will be struck by a hammer or firing pin set up of some sort.  I assumed that the striker would create a vacuum essentially and open the valve as with other air cartridges.  I honestly don't know that much about it other than what I have read on here. 

[DarwinsLaw]

There is a strong possibility that I missed something or misunderstood the Lupra design.

[rsterne]

In order for the valve to open, you must have more area at the back of the valve rod than the front.... You also need to vent the chamber behind the rear O-ring to the atmosphere to initiate the firing cycle....

The big drawback of air-cartridge designs is that they are limited in power by the small reservoir of the cartridge.... If you make that large enough, then you face terrible efficiency....

Bob

[DarwinsLaw]

Bob,
So the vent to atmospheric pressure is at the green mark, yes?

[rsterne]

Not sure, but I think that is to pressurize the small chamber surrounding the firing pin, through leakage via the threads from the main chamber of the cartridge.... When fired, the firing pin must vent that small chamber to allow the rod to move back, opening the valve....

Bob

[DarwinsLaw]

Bob,

Thanks.  That makes sense HR Buckley has some tank fill valves that work basically in that fashion where there is leakage through threads pushing an oring aside temporarily. Basically, then I just need to add another component so that I can vent to atmospheric at the rear if I am understanding you and trim the front side of the valve like this.

[rsterne]

No, the rear portion of the rod (purple part) needs to be larger than the front portion.... or there will be no net force available to move that rod back to fire.... Look at that part in the photo to see what I mean....

Bob

[DarwinsLaw]

Ah, so the purple part was fine in the first instance just need to add a component to vent to atmospheric in the striking area.  The green part should be two pieces with a small volume of air trapped inside.  I think I get it.  Thank you

[rsterne]

Nope, the rear of the purple part (where you show it inside the green part) must be larger than the front of the purple part.... Look at the part in the photo directly below the casing (= your purple part).... Compare the diameters of the O-rings, front and back....

Bob

[DarwinsLaw]

So, here is what you are meaning.  Sorry for the confusion.

[rsterne]

Yep, the rear sealing diameter (O-ring) must be larger than the front one, or the valve will have no rearward bias to make it open when the small chamber at the back drops to atmospheric pressure on firing....

Bob

[DarwinsLaw]

Bob,

Thanks for clearing that up it is much appreciated as is your patience. This drawing is rough still, but, takes that into consideration.

[rsterne]

No Problem!

Bob

[jackssmirkingrevenge]

For this to work, the gas in the pilot chamber should be able to escape quickly through the pilot valve on firing, and diameter A needs to be significantly larger than diameter B in order to have an opening bias once the pressure in the pilot chamber drop.