Two part piston

[tromic]

This is an interesting project of my friend Alex Kuznetsov and me. This was his idea. Two part piston. Only the smaller, lighter piston hits the shock absorber.

 

[popgun pete]

The blue part (a sort of unconnected piston tail) retained by the sear lever acts as a valve which opens when you pull the trigger, but the blue part cannot escape the grey coloured section. That forward movement releases the compressed air from the loading effort to flow around the valve and then drive the separate piston to the muzzle end of the gun. So the gun is now valve operated, but controlled by a sear lever and mushroom tail. My thoughts are the valve will throttle the shot until it fully opens. It is an interesting idea, but maybe it is a solution to a problem which is not really such a problem as pistons are now light compared to the all-metal versions. On loading the gun the separate piston has to push on the front of the blue part to drive it back and relatch on the sear tooth. An interesting possibility would be to have the blue part act as a pumping valve for "easy loading" as while caught on the sear tooth it can still be pushed slightly further back in the barrel. As is the valve would not open when moving the other way and if it did then there would need to be a spring to push the valve back in order to trap the already displaced air from the incomplete loading effort. Throttling will still be a problem, but "easy loading" may be an advantage for some applications. The seat for the inner "O" ring is angled on one side to produce an uneven displacement of the "O" ring for some reason when that "O" ring is pushed back on the seat.

 

[tromic]

The blue part (a sort of unconnected piston tail) retained by the sear lever acts as a valve which opens when you pull the trigger, but the blue part cannot escape the grey coloured section. That forward movement releases the compressed air from the loading effort to flow around the valve and then drive the separate piston to the muzzle end of the gun. So the gun is now valve operated, but controlled by a sear lever and mushroom tail. My thoughts are the valve will throttle the shot until it fully opens. It is an interesting idea, but maybe it is a solution to a problem which is not really such a problem as pistons are now light compared to the all-metal versions. On loading the gun the separate piston has to push on the front of the blue part to drive it back and relatch on the sear tooth. An interesting possibility would be to have the blue part act as a pumping valve for "easy loading" as while caught on the sear tooth it can still be pushed slightly further back in the barrel. As is the valve would not open when moving the other way and if it did then there would need to be a spring to push the valve back in order to trap the already displaced air from the incomplete loading effort. Throttling will still be a problem, but "easy loading" may be an advantage for some applications. The seat for the inner "O" ring is angled on one side to produce an uneven displacement of the "O" ring for some reason when that "O" ring is pushed back on the seat.

That shape of seal make it possible to O-ring on piston to act as a valve when loading the gun. It collapses under the pressure from smaller (free moving) piston.
There is a throttling, but I suppose negligible. Air flows through free area which is equivalent to hole of 6,3 mm (for 11 mm barrel).

 

[popgun pete]

I wondered about that being an air valve for progressive reloading of the gun, it could be somewhat restrictive to push air past unless the seat was cut at an angle all the way around the circumference of the rear of the seating groove. Then the inner "O" ring could fall back and open up more. During the completion of reloading when the piston physically pushes the blue part back the inner "O" ring should push forwards onto the parallel groove section to seal again. So this two part piston design is more directed at reloading than decreasing the mass of the moving piston, although that is a consequence of having no metal tail on the piston.

The "O" ring acting as a valve by sliding off its seat onto a conical shank section going one way and resealing when moving in the opposite direction is how the air pump in the Pirelli "Aries" works which uses the barrel piston to pressurize the gun before you operate a rotating switch to disable the air non-return valve at the rear end of the inner barrel and keep it open all the time for shooting.

 

[tromic]

I wondered about that being an air valve for progressive reloading of the gun, it could be somewhat restrictive to push air past unless the seat was cut at an angle all the way around the circumference of the rear of the seating groove. Then the inner "O" ring could fall back and open up more. During the completion of reloading when the piston physically pushes the blue part back the inner "O" ring should push forwards onto the parallel groove section to seal again. So this two part piston design is more directed at reloading than decreasing the mass of the moving piston, although that is a consequence of having no metal tail on the piston.

The "O" ring acting as a valve by sliding off its seat onto a conical shank section going one way and resealing when moving in the opposite direction is how the air pump in the Pirelli "Aries" works which uses the barrel piston to pressurize the gun before you operate a rotating switch to disable the air non-return valve at the rear end of the inner barrel and keep it open all the time for shooting.

Here is an another picture so you can see the idea of collapsing O-ring better.

http://s45.radikal.ru/i110/1208/e7/c2859228c22d.jpg

 

[popgun pete]

Here is an another picture so you can see the idea of collapsing O-ring better.

http://s45.radikal.ru/i110/1208/e7/c2859228c22d.jpg

I see he plans to tilt the backing edge as well as the angle on one side of the rear of the seating groove. That may be enough, he will find out when he tries it. The "O" ring will not have to move much, but the movement will be on one section rather than the entire circumference of the rubber ring.

 

[trromic]

Another idea. Maybe Italian pneumatics could be modified to use piston made all from plastic to be lighter.
O-ring on back side of piston acts as a valve to ensure creating vacuum behind of it. The vacuum diminishes the force pushing the piston against sear lever tooth.



http://imageshack.us/photo/my-images/827/laganiklip7.jpg/

 

[trromic]

This could be the simplest solution, using strong magnet.