Sump and sewage float switches have a float that raises and lowers depending on the water level in the sump basin to automatically control switch operation. When water rises to a preset level in the sump basin the switch turns on and the pump starts. When the water is drained down the switch turns off and the pump stops. Sump and sewage diaphragm switches sense pressure against the diaphragm to detect how much water is present in the basin. As the water level rises in the sump basin, the air pressure pushing against the diaphragm builds within the switch. The diaphragm switch turns on when the water rises to a specific water level and the pump starts. The switch turns off when the water is drained out of the sump basin and the pump stops. These sump pump float switches and diaphragm switches connect directly to the pump, or the pump's power cord is plugged into the switch to control electric power to the pump.
These diaphragm switches are activated by pressure within a diaphragm to start and stop pumps automatically when the water reaches a certain level. They have no moving parts, are compact so they take up little space, and require periodic cleaning since the diaphragm switch may get clogged with debris. Diaphragm switches connected to a tether are often adjustable so the pump will start and stop when the water reaches a desired level.