Choose a float switch by what it has to do and what it sits in: the wetted material against your liquid, the contact (normally open or normally closed) against the action you want on a high or low level, and a controller that can carry the load. ERE carries the Icon Process Controls plastic and stainless float, reed, tuning-fork and capacitive level switches for chemical, water-treatment and wastewater tanks, so you can match one set of part numbers to your tank before you ask for a quote.
In this guide
- What is a float switch and how does it work?
- Which float switch type fits which tank?
- Normally open or normally closed: which contact should you choose?
- Which wetted material should you pick?
- Can a float switch run a pump directly?
- When is a float switch the wrong choice?
- What is the difference between a float switch and a float valve?
- How do you install and test a float switch?
- How do you choose a float switch, step by step?
- Frequently Asked Questions
What Is a Float Switch and How Does It Work?
A float switch detects whether a liquid is above or below one set height and opens or closes an electrical contact to say so. A float rides the surface; when it reaches the switch point, it moves a magnet or a lever that operates a reed switch or a micro switch. The output is a simple on/off signal that a relay, a PLC input, an alarm or a pump starter can act on.
That simplicity is the reason to use one. A point-level switch has no calibration and nothing to drift, so it is the usual choice for a high-level alarm, a low-level pump cutout or an overflow guard. If you need to know how much liquid is in the tank rather than whether it crossed a line, you want a level sensor with a 4-20 mA output instead; see the section on when a float switch is the wrong choice below.
Which Float Switch Type Fits Which Tank?
Match the switch to how many points you need and how it mounts. The table sorts the float switches in the Level Sensors & Switches collection. Figures come from the product records; lengths, part numbers and contact options are confirmed on a quote.
| Model | Switch points | Contact / output | Wetted material | Length or range listed | Best for |
|---|---|---|---|---|---|
| FloatPro LP25 | 1 (optional weights for multi-point level) | Reed or micro switch; normally open or normally closed | PP float, PVC cable | Cable length specified at order | Simple high or low level in a chemical tank or sump |
| PLA | 1 | Normally open or normally closed relay; visual alarm light; 24 VDC | PVC, PP, PVDF or 316 SS | 6 to 72 in; 0.5 to 6 ft operating range; 2 in NPT | A local, visible alarm on a day tank |
| PLF | 1 to 8 | Relay contacts, up to 8; no power required | PVC, PP, PVDF or 316 SS | 6 to 72 in; 2 in NPT or flange | Several levels on one stem: pump on/off plus high and low alarms |
| PLS-V | 1 | Hermetically sealed reed switch | PP or PVDF | 1/8 in vertical connection | Compact high or low level indication |
| PLS-H | 1 | Hermetically sealed reed switch | PP or PVDF | 1/2 in horizontal connection | Side-wall mount in a tank or sump |
| PLS-ES | 1 | Hermetically sealed reed switch | PP or PVDF | 12, 24, 36 or 48 in shaft | Deeper tanks, top mount |
The PLS family is all plastic, and the records list mounting within 45 degrees of vertical. If you cannot get the float free to travel, a different technology is the better tool.
Normally Open or Normally Closed: Which Contact Should You Choose?
Choose the contact so that a failure reads as the unsafe condition. A normally closed circuit that is supposed to stay closed in normal operation tells your controller something is wrong the moment a wire breaks or a connector corrodes, because the loop opens. A normally open circuit would read the same fault as "everything is fine."
In practice that means picking by the action, not by habit. For a low-level pump cutout, wire it so the pump stops if the loop opens. For a high-level alarm, wire it so a broken loop raises the alarm. The LP25, PLA and PLF are all listed with a selectable normally open or normally closed contact, so you can set this at order. State the contact and the action when you request a quote.
Which Wetted Material Should You Pick?
Pick the material your liquid will not attack at your operating temperature. The PLA and PLF list PVC, PP, PVDF or 316 stainless steel; the LP25 uses a polypropylene float; the PLS family lists PP or PVDF. Plastic suits most water-treatment and chemical-feed tanks, and 316 SS is there for the services plastic cannot take.
No product record replaces a compatibility check. Read the Safety Data Sheet, which suppliers must provide under WHMIS, and the manufacturer's chemical-resistance chart for the exact material. If the chart is silent for your mix or concentration, send us the chemical, concentration and temperature and we will confirm with the manufacturer. The LP25 record does not list a temperature limit, so ask us for it before you specify it for a hot tank.
Can a Float Switch Run a Pump Directly?
Only if the switch's contact rating covers the pump's load, and the records for these switches do not list one. Treat the float switch as a signal device and let it drive a relay, a contactor or a PLC input, which then carries the pump current. This protects the contact from inrush and from arcing, and it keeps one fault from taking out both the switch and the motor.
The PLA is the exception that shows the pattern: it is listed on a 24 VDC supply with a relay output, so it belongs in a control circuit rather than across a pump. The PLF is listed as needing no power and connecting directly to a PLC or relay controller. Confirm the contact rating on the manufacturer datasheet before you wire anything to a motor, and keep enclosure ratings in mind: the PLA and PLF junction boxes are listed as NEMA 4X / IP67, which you can check against NEMA and the IEC 60529 ingress-protection (IP) code.
If you came looking for a replacement float for a household sump pump, this is not that product. ERE supplies process instruments for water, wastewater and chemical tanks, not residential pump-mounted floats.
When Is a Float Switch the Wrong Choice?
When the liquid will foul, trap or foam around the float, or when you need a reading rather than a trip point. The PLA and PLF are listed for non-viscous, non-coating liquids. In sludge, oil, polymer or a coating chemical, a float can stick, and a stuck float reports the last position it held.
- Foam, turbulence or viscous liquids: the Icon TFS tuning-fork switch is a vibrating fork in 316 SS or PTFE-coated, with SPDT relay or pulse output, listed for liquids to 10,000 mm²/s and for use through foam and turbulence.
- Coating liquids, no moving parts: the AlertPro is a capacitive alarm on a PVC or CPVC shaft with adjustable switch points, and the NC31 is a capacitive level and leak switch with an NPN output.
- Sensing from outside the tank: the NC30 senses liquid through plastic or fiberglass walls up to 0.3 in (8 mm) and pipes up to 2 in, and the NC-15 / NC-25 clamp onto 1/4 to 1/2 in tubing for dosing lines.
- A continuous reading: the CFL float level sensor gives a 4-20 mA output with ±2 mm accuracy over 6 in to 6 ft. For deeper or larger tanks, the UltraPro 500 ultrasonic and the ProScan 2 radar transmitters are in the same collection, and the ITC 450B level controller turns a 4-20 mA input into a display and two relays. Scaling and wiring a 4-20 mA loop is covered in our 4-20 mA pressure transmitter buyer's guide.
What Is the Difference Between a Float Switch and a Float Valve?
A float switch sends a signal; a float valve acts on the water itself. The Icon FloatPro ball float valve is a polypropylene valve with an adjustable arm that opens and closes the fill line as the level moves, with red and green status lights, in 1/2 in and 1-1/2 in sizes. It holds a tank level mechanically with no controller. Use a valve to hold a level; use a switch when something else, such as a PLC or an alarm, has to know about it.
How Do You Install and Test a Float Switch?
Mount it where the float can move freely and the liquid is calm, then test it by hand before it goes live. Keep the float away from the inlet stream, agitators and the pump suction, which push the float around and give false trips. A stilling tube around the float helps in a turbulent tank.
- Confirm the mounting orientation on the datasheet. The PLS reed switches are listed for within 45 degrees of vertical.
- Set the length so the float reaches the trip height you want, and leave clearance from the tank wall and any other fittings.
- Wire through a relay or PLC input, not straight across a motor, unless the datasheet contact rating covers it.
- Lift and lower the float by hand with a meter on the circuit and confirm the contact changes at the height you set.
- Add the switch to your periodic test routine. A float that never moves can look healthy for years until the day it is needed.
How Do You Choose a Float Switch, Step by Step?
- Name the liquid and temperature. Liquid, concentration and operating temperature decide the material.
- Check compatibility. Read the SDS and the manufacturer's chemical-resistance chart.
- Decide how many points. One for an alarm or cutout, several for pump control with alarms.
- Choose the contact. Pick normally open or normally closed so a failure reads as the unsafe state.
- Check the liquid is float-friendly. If it foams, coats or is viscous, choose a tuning-fork or capacitive switch.
- Set length and mounting. Match the stem length, connection and orientation to the tank.
- Plan the wiring. Use a relay or PLC input unless the contact rating covers the load.
- Send the details. Quote by model, material, contact and length and we confirm availability and bulk terms.
Need a float switch for a chemical or water tank?
Send us the liquid, temperature, number of switch points, contact and length and we will confirm the model, part number and availability.
Frequently Asked Questions
How does a float switch work?
A float rides the liquid surface. When it reaches the switch point it moves a magnet or lever that closes or opens a reed or micro switch, giving an on/off signal to a relay, alarm or PLC.
What is the difference between a float switch and a level sensor?
A float switch tells you whether the level crossed one set height. A level sensor, such as a 4-20 mA transmitter, gives a continuous reading of how much liquid is in the tank.
Should I choose a normally open or normally closed float switch?
Choose the contact so that a broken wire or a stuck float reads as the unsafe state. A normally closed loop opens on a fault, which a controller can detect.
Can a float switch be used in chemicals?
Yes, if the wetted material is compatible. The PLA and PLF list PVC, PP, PVDF or 316 stainless steel, but you should check the SDS and the manufacturer's chemical-resistance chart for your exact liquid and temperature.
Do you quote float switches across Canada?
Yes. Send the model, material, contact, length and quantity through the quote form and we confirm availability and bulk terms for delivery across Canada.
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Lire en français : Interrupteur à flotteur : guide de choix selon le type de flotteur, le matériau mouillé et le contact au Canada