SpudFiles

I was reading the principle of gas blow back article on red wolf. http://www.redwolfairsoft.com/redwolf/a ... viewID=199

I understand all of it except for one part.





They claim that the floating valve, the silver part that moves forward when firing, doesn't move until the bb has left the barrel. How can that be? Apparently somehow the pressure is keeping it from moving. But how?

In my head, the whole mechanism is similar to a QEV valve (there is no pilot valve and stuff), with the barrel attached to the pilot port. The valve is not pressurized, pressured gas rushes in from the fill port when the hammer valve is hit, some gas escape through the pilot port into the barrel, creating a pressure difference hence "wind" that pushes the piston forward, closing the pilot port (barrel) and directing the rest of the gas to the bolt carrier.

I don't see how pressure can keep the floating valve back when the bb is still moving down the barrel. Isn't there already a pressure difference as the bb is moving, and thus the floating valve should close?

Before the BB left the barrel, there is pressure between the floating valve and the BB which counters the pressure from the main valve to the floating valve, preventing it from moving. Once the BB has left the barrel the pressure between the BB and the floating valve is gone and the pressure from the main valve side pushes the floating valve shut.

but I'm thinking the pressure between the bb and the floating valve is less than the pressure between the floating valve and the hammer. As the bb travels down the barrel, the volume between the bb and the floating valve increases and there is a pressure difference.

No the pressure in the barrel is greater than you think, you can check using GGDT.

wait, it doesn't matter how great the pressure is, the gas is coming in through the floating valve into the barrel. For the gas to flow, there must be a difference in pressure, higher at the valve than the barrel.

You actually gets a pretty high pressure inside the barrel as the gas rushes into a shallower space.

what? how do you get high pressure from gas rushing in? Moving gas is low pressure, and the moving gas is what closes the valve?

I sort of understood where you don't understand but I'm not good enough to explain it right, plus I didn't look into the diagrams long enough, after all barrel pressure isn't involved here the way I thought.
The floating valve starts to move as soon as the hammer valves is opened (The inner diameter of the floating valve is less than the outer diameter) but since it's heavier than the BB and there is a slight spring tension it will shut off the flow after the BB left the barrel (at least the manufacture should design it that way).

Ok, it's not a very good explanation, but I'll take it. I thought you'd know more about it since you work on the we system.

Edit
So the common explanation is wrong, the floating valve starts closing as soon as the hammer valve is struck, and closes completely by the time the bb leaves the barrel, at least by design. The bb inside the barrel really only has an effect on how fast it closes.