Float switch (liquid level float switch)

01

Choose float type and switch rating

Jiukang describes its cable float level switch as connected to a pump through its cable for automatic control and dry-running protection of water towers and pools, with switching range adjusted by moving a locating piece on the cable and a counterweight, for water, sewage, mild acid or alkaline solutions and oils; it states an operating voltage of 200 V and current up to 10 A, and warns never to immerse cable joints. [2]

Aether describes magnetic floats as floats containing a permanent magnet whose movement with the liquid operates reed switches or magnetic sensors, offered in polypropylene (PP), nitrile rubber (NBR) and stainless steel, for level measurement, pump control and valve control. [3]

Editorial note: compare the switch's rated voltage and current with the pump or contactor coil it will drive; where the pump current is higher than the switch rating, use the float to signal a relay or controller.

Give the supplier the liquid (water, sewage, oil, chemicals) and temperature, tank or sump depth and mounting, the levels to detect (start, stop, alarm), whether the float drives a pump directly or signals a control panel, voltage and current, cable length, float material, approvals and any explosion-proof requirement.

02

Set pump start, stop and alarm levels and prevent fouling

US patent 6,464,465 (Level control device for a wastewater collection basin) describes a pump station using float devices, each a buoyant housing with a switch, positioned at its elevation by a lead weight on its insulated cable and hung from a stainless steel bracket; the cables carry open or closed signals to control relays, which signal the pump motor starter to run as the level rises and stop as the 'off' float opens. It notes that grease and other waste accumulating on floats can affect operation, and proposes heating the float surface to about 80–110 °F to resist build-up. [1]

Editorial calculation: in a sump where the pump-on float is set 1.2 m and the pump-off float 0.4 m above the floor (assumed figures), each cycle removes the liquid in a 0.8 m band; for a 2 m × 2 m sump that is 2 × 2 × 0.8 = 3.2 m³ per cycle, which together with inflow sets how often the pump starts. [1]

Editorial note: add a separate high-level alarm float above the pump-on level, keep floats clear of inflow turbulence and each other, and include float cleaning in maintenance where grease or solids are present.

03

Confirm the switch element is mercury-free where the law requires it

Older tilt float switches could use a mercury switch element. Maine law, 38 MRSA §1661, defines a mercury switch to include “mercury float switches actuated by rising or falling liquid levels” and mercury tilt switches actuated by a change in switch position, and 38 MRSA §1661-C(7) provides that, effective July 1, 2006, a person may not sell, offer to sell or distribute a mercury switch or mercury relay individually or as a product component. The ban does not apply to a switch used to replace one in a larger product that was in use before July 1, 2006, where that product is used in manufacturing or the switch is integrated and not physically separate, or where use of the switch is a federal requirement; makers or users may also apply for an exemption. [4]

Aether's magnetic floats above use reed switches; for cable floats and any other type, ask the supplier to confirm in writing that the switch element contains no mercury. [2] [3] [1]

Editorial note: this section quotes Maine's statute as one published example; check the mercury product rules of each destination market.

For North American projects, ask for a declaration that the float switch is mercury-free and the switch technology used (micro-switch, reed or other).

04

Four float switch makers and what each lists beside them

The 200 V / 10 A rating and the PP, NBR and stainless float options quoted above come from the Zhejiang Jiukang Electric Co.,Ltd and Ningbo Aether Sensors Co., Ltd pages; the CNC Electric and Andeli Group Co., Ltd. cards give no figures to compare. [2] [3]

The suppliers reviewed list cable float switches and magnetic float level sensors; ask each for switch type and rating, float material and liquid compatibility, temperature and pressure limits, cable type and length, mounting, and approvals.

05

Float, switch element, magnet, cable and relay

The switch row is where tilt and reed designs part ways; the cable-and-counterweight row applies to tilt floats, whose switching range Jiukang sets by moving a locating piece on the cable. [2]

06

Float switch ratings with and without published values

Contact resistance, insulation resistance and dielectric strength have no published value in the sources here; ask for them together with the switch voltage and current, which Jiukang does state. [2]

07

Send the liquid, level and load data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Liquid: [type; temperature; solids or grease]
Tank: [depth; mounting]
Levels: [start; stop; alarm]
Load: [pump direct or relay; V; A]
Float: [type; material]
Cable: [length; sheath]
Approvals: [CE; UL; Ex]

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