Float switch

Another common type is a float that raises a rod to actuate a microswitch.

If the liquid continues to rise (perhaps because the pump has failed or its discharge is blocked), the second stage will be triggered.

In some cases, a rod through a stuffing box can be used to operate a switch, but this creates high drag and has a potential for leakage.

Float switch materials are selected to resist the deleterious effects of corrosive process liquids.

In some systems, a properly selected and sized float can be used to sense the interface level between two liquids of different density.