Variable pressure _and_ volume?

[soilent green]

Its funny I was just thinking of this today and now I see this post and while reading this I was thinking of my old m98 and its velocity adjuster to But what I am also woundering is about air efficency I was thinking about the size of the mag chamber and if runing at high pressures and smaller chambers could help it and then I started thinking of "low pressure cockers" and why they were supposedly so air efficient so guys what do you think about this

[athomas]

There's a couple of methodologies available to limit pressure behind the ball.

1. Decrease the available chamber pressure. This has a direct effect on the pressure behind the ball. We now require a greater chamber volume to produce acceleration over a longer period of time.

2. Decrease the cross sectional area of the bolt/valve opening. The properties of thrust and the compressability of air/gases say that the exit pressure at the exit end of a tube is related to the size and material/smoothness of the tube. That is, if you decrease the size of the tube, you will decrease the available pressure at the exit to the tube. The end result is that the higher chamber pressure will exit at a lower pressure and be available for a longer duration the same as a larger lower pressure chamber.

Again we have to determine the most advantageous combination of chamber pressure , chamber size, and valve tube size to obtain optimum performance.

If we have too high a pressure we have to limit the valve tube size and this increases the friction which is a result of higher air velocity. An increase in friction is a loss in efficiency.

If we have to low a pressure we have less of a pressure differential. We need a pressure differential to have any acceleration. The end result is that more air is required to accelerate the ball over a longer period of time. Think of how long you would have to blow on a barrel to accelerate a ball to 300 ft/sec. It wouldn't happen. The air you expelled would be wasted, therefore making your blowgun very inefficient. The closer a paintball gun gets to regular air pressure the less efficient it gets.

In conclusion here. Since both ideas get inefficient at the extremes, we can conclude that somewhere in the middle we will have perfection.

[AGD]

Athomas,

Decreasing chamber volume lowers the pressure against the ball only if everything else stays the same. It is a simple matter to restrict the flow more or less to get a wide range of pressure behind the ball regardless of your chamber pressure.

All you really need to determine is what acceleration profile you want on the ball, the rest falls into place after that.

AGD

[athomas]

Yes, exactly. That is what I was saying, although it may have gotten mixed up in the rest of the message.

I was just stating that there are various ways to achieve the lower pressure phenomenon that everyone is trying to achieve. Each has a consequence.