How it works: In order for you to use it correctly, please follow our instructions: 1.Cool the soda machine Cylinder in the freezer for 1 hour. 2.Screw the CGA320 or W21.8 connection to a commercial CO2 gas cylinder. 3.Disconnect the quick connector of the black adapter, and then tighten the black adapter to the CO2 cylinder( must turn the knob on the top of the black adapter to the highest position,the whole process does not need to turn the adapter knob down to open the CO2 cylinder,If the adjusting rod press down 6mm wide valve pin, this will close the valve and CO2 cannot enter) 4.Connect the quick connector 5. For most big cylinders: turn the big cylinder upside down or lie it down.some host tank has not the dip or syphon tube inside. 6.Carefully Open the valve of the large gas bottleThe valve on the CO2 Cylinder closes the flow if it is opened to much. This will happen if you open the big cylinder too much or too fast. The trick is to open the big cylinder very carefully. You will hear the air flow. So to fill it successfull 7.After about 15-20 sec., The cylinder is completely filled 8.Close valve of the large gas bottle 9.Opening the bleed screw to drain residual gas 10.Unscrew the CO2 cartridge done Please note: 1.If there is liquid CO2 inside the cylinder, please upside down your CO2 tank if you can not refill when the CO2 tank standing,because some of tank have not the dip tube (syphon tube)inside. 2.The cylinder should be empty.Pre Cooled cartridges will get quite full. 3.need to open the tank valve very slowly when you filling the protection valve(6mm wide pin) of soda machine bottle. 4.Our adapter don't work RPV valve (residual pressure valve),please find picture as follow,but some of RPV valve can be removed by hex wrench,please check before ording. If your big tank has a RPV valve,you can choose "RPV pushing adapter" in option to make order.