Plug in the pump and attach the clear tube of the pump to the valve. Turn the switch on the power supply to ascertain that the alarm is working properly. Then, pump out the air inside the bell jar. It will take about 5 minutes to obtain a low enough air pressure so that the alarm will not sound. Turn the alarm on and slowly open the valve, allowing the air pressure in the bell jar to increase. The sound of the alarm will also gradually increase.