Volume And Pressure

[sixshootertexan]

I have been researching mods to valves. I see on the 22xx valves that some are modding the valve by removing unnecessary metal to increase volume resulting in more velocity. I understand flow improvement to get the CO2 from one place to the other efficiently. My question would be at what point would you be just wasting the CO2 by increasing the volume of the valve? 1%, 10% or 25% of a volume increase? Next question is how much does velocity increase with the increase of pressure? Say going from 1000psi to 1500psi then to 2000psi.

This is just the hamster running in the wheel that's inside my head. I just like to really figure out how things work. Everything I ever get into I'm that way about. Just crazy old me.

Ricky

[TimmyMac1]

It is poinmtless to dump the whole charge as you have very low average pressures. If you have larger volume, the pressure drop during the firing cycle is less while the average pressure is higher resulting in better power.
Every exhaust valve will have a ideal prsssure it likes and that pressure should not be exceeded.
If you have adequate volume the performance will be good and the valve will shut fast.
The sure sign that you have gotten it wrong is a noise that is more fart than crack.
The less the pressure drop the less the shock to the system from the drop and the valve closing/repressurising.
Air has mass and it is in motion till the valve shuts. The more fluid (less wasteful)this transition is, the better the system operates.
Porting, pressure, volume and ultimate restriction point(s) all conspire to make your system work good or not.
You are always attempting to create a valve volume/duration that matches the time a pellet spends on the bore.
The more power you want to make the more pellet weight and air volume/presure you need(all other things being held equal).
Pnuematics don't work as efficiently as Springers with light ammo so the best approach is with Projectal mass rather than speed.
The moral to the story is go heavy/hard not light/fast. When you have a system that shoots the pellets with the highest BC at the highest power you want to take advantage of that relationship.

[rsterne]

Your question depends mostly on the barrel length.... There is little point in trying to increase the volume on a 2240 with an 8" barrel as a lot of the CO2 is already just blowing out the barrel after the pellet has left.... It's a different story with a 2260 with a 24" barrel.... Depending on other mods, more volume could increase velocity....

Your next question, about pressure, is obviously not about a CO2 gun, because CO2 is a constant pressure unless you change the temperature (850 psi at 70*F).... Here is a graph I did measuring the velocities with a 14" and a 24" barrel on HPA with three different hammer springs.... It shows the relationship between pressure and velocity.... and the effect of barrel length.... That relationship changes with different springs as each spring becomes incapable of opening the valve fully as the pressure increases.... 



Each spring has a different pressure where the velocity "rolls over" and starts to decrease because the (higher) air pressure inside the valve is starting to close it.... A stock 2240 spring peaks out at about 1200 psi.... a 2289/1377 spring at about 1400 psi, and a Disco spring at about 1600 psi (with 14.3 gr. pellets).... The valve I used was a dead stock 22XX valve, it even had the piercing pin still in place.... so the volume was just the stock internal volume.... Here is a photo....



HTHs....

Bob

[sixshootertexan]

Thank you Gentlemen. That cleared up a few things. Never really thought of it as just a reservoir, because I was thinking along the lines of a pump style gun that does release all of it stored compressed air. We use small tanks at each of our machines at work for the same purpose so when the tool changer is activated the pressure will not drop enough to cause the low air pressure alarm to trip.

Again Thank You