bracket 180 mounted to bell 160 through bolts 170 has forced bell 160 into engagement with the top of can 140 in still further preferred embodiments arcuate slot 220 is fashioned so as to contain an unstable point of equilibrium 320 for cam roller 230 when cam roller 230 falls on unstable equilibrium point 320 as roller 300 forces actuating cam 210 to move cam roller 230 is forced into the position shown in fig3 thereby forcibly engaging bell 160 with can 140 in this manner arcuate slot 220 having unstable equilibrium point 320 is assured of fixedly securing bell 160 to can 140 during the filling process unstable equilibrium point 320 within arcuate 220 is particularly necessary for filling valves provided in accordance with this invention which utilize sealing rubbers located within bell 160 sealing rubbers for use in counterpressure filling machines and filling valves are taught in u s pat no 4 750 533 yun which is specifically incorporated herein by reference thus unstable equilibrium point 320 which in preferred embodiments is located substantially around the center of arcuate slot 220 ensures that cam roller 230 is forced into the position within arcuate slot 220 that causes actuating cam 210 to securedly fix bell 160 onto the top of can 140 during the counterpressure filling process referring to fig4 a filling valve provided in accordance with this invention is fixedly mounted through flange 370 to the bottom wall 330 of reservoir 70 by bolts 340 reservoir 70 contains carbonated liquid 350 which is dispensed to can 140 during operation of the filling machine a counterpressure gas 360 at elevated pressure typically nitrogen or carbon dioxide at 40.