the open end of a plastics bag or like container is sealed by inserting the open end into the mouth of a sealer which welds the plastics film by the application of heat and pressure . upon detection of the presence of a bag in the mouth a control unit initiates a sealing cycle . the user has available a film selection switch , linked to the control unit , to enable different film materials to be sealed satisfactorily . the sealing pressure , the sealing temperature and the duration of the sealing action are parameters which affect the sealing . these are independently controllable and presettable to cater for different film materials . the choice of the switch setting causes the control unit to initiate a sealing cycle with appropriate values for each of these parameters .