Float Level Switch

The float level switch is the workhorse for level alarms and pump control on tanks, drums and boilers. A float rises and falls with the liquid; a magnet in the float or on its arm operates a hermetically sealed switch on the dry side of the pressure boundary, so there are no seals or glands to leak. With up to four switches on one unit, a single nozzle provides the high, high-high, low and low-low alarms that a typical vessel needs.

Switches cover ranges from 100 to 4,000 mm with set-point adjustment of ±20 mm, at process conditions to 50 bar and 400 °C. Materials are carbon steel, 304 or 316 stainless steel, with polymer-coated options for corrosive service. Mounting is side-side, side-bottom, top-side or top-bottom with flanged, threaded or weld-stub connections, either directly in the vessel or in an external cage that can be isolated for testing. Contacts are SPDT or DPDT with ratings to suit the control system. Anti-frost protection and cooling fins adapt the switch to cryogenic and hot service.

A float of suitable density set at the boundary between two liquids gives an interface switch.

Applications are level and interface control and alarms in storage tanks, drums and boilers in oil and gas, chemical and power generation. For higher pressures or a tighter set point, see the displacer level switch.