We were having difficulty in getting a glass bell jar. Finally we decided to use a SS container with a 5mm acrylic dome with compact PVC gasket held in place with C clamps. For all threaded joints we used shellac. The entire cycle of switching of vacuum pump on / off and air release are done through three cam switches driven by a 1 rpm motor .Recently we have added a Solenoid valve after the pump so that oil vapors do not enter the jar when the pump is in off position. For bell we have used one from old type telephone ringer with gongs which we used to supply to ITI.