Valve Design

[CableStop]

I thought of this valve as a solution for a double barrel airgun since you can fit two side by side and actuate each with its own hammer without needing two air tubes.  It's kind of an adaptation of the Air Force style valve that can be opened from the rear.

[Rob M]

reminds me of the action pistol spool valves.. theres one in the crosman vigilante and 100 other action pistols.. they fire through the center of the stem.

i could be misunderstanding the drawing .

[MJP]

Looking at the design, I would say it's a dump valve.
O ring at the barrel end has more surface area than the stem so once open it blows completely open and stays that way until reservoir pressure times surface area is below the spring pressure.

Marko

[CableStop]

Looking at the design, I would say it's a dump valve.
O ring at the barrel end has more surface area than the stem so once open it blows completely open and stays that way until reservoir pressure times surface area is below the spring pressure.

Marko

I think it should work like any other valve, the poppet sits on a seat like normal it's just that after the air passes by it, it turns 180 degrees and flows out the front.  The green circle near to the stem is the inlet hole that lets air flow into the pass through, when the valve is shut that hole is covered.

[CableStop]

reminds me of the action pistol spool valves.. theres one in the crosman vigilante and 100 other action pistols.. they fire through the center of the stem.

i could be misunderstanding the drawing .

I'm not sure how those work honestly, I've never seen one taken apart.  This valve basically uses a hollow poppet and when it's open air can flow through it and into the barrel, the stem itself is solid.

[sb327]

Looking at the design, I would say it's a dump valve.
O ring at the barrel end has more surface area than the stem so once open it blows completely open and stays that way until reservoir pressure times surface area is below the spring pressure.

Marko

I think it should work like any other valve, the poppet sits on a seat like normal it's just that after the air passes by it, it turns 180 degrees and flows out the front.  The green circle near to the stem is the inlet hole that lets air flow into the pass through, when the valve is shut that hole is covered.

I mostly agree that it will act MOSTLY like a dump valve…. But…. If you consider that oring on the right will see pressure on both sides during the shot cycle, it MAY behave depending on how large the projectile and other factors. If a very light projectile or dry fire, it’s probably gonna be a toss up.

Also note though, Airforce guns can get uncontrollable given certain conditions as well.

A larger stem could be a tuning option to get it to behave though.

Dave

[CableStop]

I mean if the front o-ring is in an ID groove in the valve body wouldn't that solve any issues with the air pressure?  I don't think you could groove the poppet outlet tube because the walls need to be fairly thin to allow as much airflow as possible. 

[sb327]

I mean the piston effect located at the area of the right side oring. This is a force that acts to ‘open’ the valve.

Dave

[MJP]

You have surface area before the feed hole, and it is limited to the o ring, pressure is pushing on that area.
Air is expanding after that feed hole as the projectile is moving out the barrel.
It is reducing pressure in the barrel, and the feed hole is a choke point, pressure is higher before that point.
If the valve is still open when the bullet is gone, it won't close, flow is keeping enough pressure differential to keep it open.
Bigger stem and the problem goes away.
I would suggest a different approach, barrel type valve that selects the bore you want to shoot, and one valve that feeds both barrels.

Marko

[sb327]

As drawn, the small port shown in the poppet would be a choke point. But I don’t assume these type of drawings to be to scale or ultimately the final design.

That port can be made larger to equal full bore.

Other tidbits need to be considered as well but that would be further into developing the idea on paper.

Dave

[MJP]

The reason I pointed out the choke point is the fact some AF valves are exactly like drawn here.

If the OP has been looking one of those for ideas.
Drawing is always the first step, or should be and then calculating the desired dimensions.

Interesting idea with two barrel design, I hope we see more than just a picture on paper.

Marko

[CableStop]

I see what you mean now I was totally missing the point.  So the stem area has to offset the force on the rear of the poppet since the front face doesn't have pressure on it. 

On the note of choke points, I think you would use multiple holes around the circumference of the poppet tube not just one as shown in the drawing.  I just showed one to make it easier to draw.