Plenum Volume Confusion

[thomasair]

So just an FYI, this is a non linear problem. If you've taken a differential equations you can relate this to a tank mixing problem.

The other thing to remember is you are dealing with a compress able fluid. Not water. When you up the pressure of air, the amount of air does not scale linearly. Conversely a plenum is regulated. This you fix the pressure and increase the tank volume. But the gas volume does not increase proportionally to the tank volume. To maintain the same pressure of air across a larger volume you need a MUCH larger quantity of air.

Thus to tie it back to the original question. The key is the compression of the gas that yields higher shot count.

An easy anecdotal thing you can try out is get two air rifles with different tank sizes. A tank size of 150 CC does not take half as long to fill up as a tank size of 300 cc

Pressure and volume in a closed system are, in fact, proportional.

There is exactly double the amount of air in a 300cc tank at 3000 psi compared to a 150cc tank at 3000 psi.

Mike

 

[JimD]

Yes I think a larger mass and volume of air will come out of a larger plenum but it gets a little complicated because the higher pressure in the plenum should also close the valve quicker. The same mass of air at higher pressure will have lower volume. So several things are a little different and not all in the direction of increasing velocity. But velocity increases, that is the biggest effect. The bigger plenum will not fall in pressure as fast when the valve opens. So the pressure behind the pellet will also not decrease as quickly.