im trying to think about how you would sweep the same volume with this arrangement. The initial seal ( once the piston oring passes the tiny weep hole ) is your total volume.. I think id have to see a drawing,.
what this does is change the geometry from the pump arm to the piston travel ( lessens the angle at the time the pressure rises dramatically
does this tube need to hold a certain pressure? it seems like you guys are talking about low working pressure tubes?
Quote from: darkcharisma on July 19, 2018, 06:56:41 PMdoes this tube need to hold a certain pressure? it seems like you guys are talking about low working pressure tubes?Duy,The pressure needs to be high enough to overcome initial pellet resistance, static and dynamic friction down the barrel, to achieve a reasonable velocity. The exact peak compression pressure is a design choice, set by the degree of compression (compression ratio).As regulated PCP often work at 1500 PSI and CO2 guns work at about 900 PSI, working pressures around 1000 PSI for a single stroke pneumatic are clearly feasible.Now, in playing around with the Beeman P17 single stroke pneumatic pistol, it is clear that by increasing the compression ratio, more energy is stored and released in the form of a faster pellet. The side effects are that the peak cocking force becomes uncomfortably high, at some point the mechanism will yield from being over-stressed.Your question does point to one very significant consideration: As the pressure in the first 95% of the tube length is almost insignificant for a single stroke pneumatic, the tube wall in that section can be very thin. It is only in the last inch of tubing that pressure starts building "fast". As such, the tube can be light, with just the last section encased in a secondary tube to handle pressures up to the design peak pressure; including a reasonable margin of safety.The margin of safety does not need to be as high for a 200 CC compression tube as for a 200 CC pressure vessel at similar peak pressure. This is because, rather than the whole 200 CC being at 1500 PSI, only 2 CC would be at that pressure. If the tube failed in the latter case, only one hundredth of the energy would be released. This makes sense, as a typical 200 CC pressure vessel would be at used from 3000 PSI down to 1500 CC, to launch 100 12 ft.lb pellets; while a 2 CC air volume at 1500 PSI can only launch one 12.ft.lb pellet.
yeah when the forum asked me if i wanted to reply to a 120 old thread. i said why not. lol. it shows you guys are still rock solid with airgunning! did i miss the conpletiong of the project??