I just bought a Ridgid SP-330D Sump Pump. This is the one with the "Diaphragm Switch." Though I can make it run by sticking a pen top into the bottom of the diaghragm unit, I cannot get it to turn on by just sticking it in the water. Does anyone out there know anything about this "Diaphragm Switch," and how it is supposed to work?
A diaphragm switch works on the pressure created by the water across the diaphragm. The switch cavity behind the diaphragm must be vented to air. There is a tube from the back of the switch to the plug on the cord. If that tube is plugged by anything (i.e. a bug, spider web, or water that you may have gotten in it if it dropped in the water when installing or it may be pinched some way or it may be kinked). What happens is the air behind the diaphragm can not get out and the pressure behind it equals the water pressure in front of the diaphragm and the switch can not turn on.