Understanding the Different Types of Float Switches

Float switches are small components with an extremely important job. They automatically start or stop a pump when water reaches a certain level.

Float switches are commonly found in sump pits, sewage basins, septic systems, holding tanks, cisterns, water-storage tanks and many other pumping applications.

Although many float switches look similar, they are not all designed to perform the same job. Choosing the wrong switch can lead to short cycling, unreliable pump operation, overflowing tanks or a pump continuing to run after the water is gone.

What Does a Float Switch Do?

A float switch senses the level of liquid inside a pit, tank or basin. As the water rises or falls, the float changes position and opens or closes an electrical circuit.

Depending on the system, the float switch may:

• Start or stop a pump

• Activate a high-water alarm

• Protect a pump from running dry

• Control the filling of a tank

• Send a signal to a pump-control panel

• Start a backup pump during a high-water condition

It is important to understand that not every float switch is designed to power a pump directly. Some switches are designed to carry the electrical load of the pump motor, while others are only intended to send a low-voltage or low-current signal to a control panel.

1. Tethered Float Switches

A tethered float switch hangs from its electrical cable and tilts as the water rises or falls.

The amount of cable between the mounting point and the float determines how far the float can travel before turning the pump on or off.

Tethered floats are sometimes called:

• Cable floats

• Wide-angle floats

• Variable-level floats

• Mercury-style floats, although many modern versions do not contain mercury

Tethered float switches are commonly used in:

• Large sump pits

• Sewage basins

• Septic pump chambers

• Effluent tanks

• Holding tanks

• Large water-storage tanks

The main advantage of a tethered float is that it can provide a larger distance between the pump’s starting and stopping levels. This allows the pump to run for longer periods and may help reduce frequent cycling.

The disadvantage is that the float requires enough room to move freely. It can become caught against the pump, discharge pipe, electrical cord, tank wall or debris inside the basin.

A tethered float should always be positioned where it can rise and fall without obstruction.

2. Vertical Float Switches

A vertical float switch moves straight up and down along a fixed stem or guide.

Unlike a tethered float, it does not swing across the basin. This makes it useful in narrow pits or confined spaces.

Vertical float switches are commonly used in:

• Narrow sump pits

• Compact pump chambers

• Residential sump-pump systems

• Basins with limited movement space

• Installations where a tethered float may become tangled

Vertical switches generally stay close to the pump or discharge pipe, making them less likely to become caught on another component.

The downside is that many vertical floats have a smaller distance between their starting and stopping positions. This can cause the pump to cycle more frequently, especially when water is entering the basin quickly.

3. Diaphragm Switches

A diaphragm switch senses water pressure rather than using a freely moving float.

As the water rises around the switch, pressure pushes against a flexible diaphragm. This activates an internal electrical switch and starts the pump.

Diaphragm switches are commonly used in:

• Small sump pits

• Pumps with built-in automatic controls

• Confined basins

• Applications where a hanging float may become obstructed

Because there is no float swinging inside the basin, diaphragm switches can work well in tight spaces.

However, dirt, sediment, mineral buildup or mechanical wear can affect the operation of the diaphragm over time.

Some diaphragm switches are built directly into the pump, while others are separate piggyback switches that allow a manual pump to operate automatically.

4. Double-Float Switches

A double-float switch uses two separate floats to control the pump’s starting and stopping levels.

The upper float normally starts the pump, while the lower float determines when the pump shuts off.

Double-float switches are useful for:

• Larger sump basins

• Tanks requiring a wider pumping range

• Applications where short cycling is a concern

• Systems requiring more precise start and stop levels

• Pumps that need to run longer during each cycle

A double-float arrangement can provide a much greater pumping range than a compact vertical float.

This allows more water to collect before the pump starts and more water to be removed before it stops.

Reducing the number of pump starts may help reduce wear on the motor and electrical components.

5. Narrow-Angle Control Floats

Narrow-angle floats require only a small amount of movement to change their electrical signal.

These floats are commonly used with control panels, pump alarms and multi-pump systems.

Narrow-angle floats are often used for:

• High-water alarms

• Low-water shutdown protection

• Duplex pump systems

• Sewage lift stations

• Septic control panels

• Cistern controls

• Tank-level monitoring

A larger pumping system may have several floats installed at different heights.

For example, one float may stop the pump, another may start the primary pump, another may start a backup pump and the highest float may activate an alarm.

Control floats are often designed to signal a relay or control panel rather than power the pump motor directly.

6. High-Water Alarm Floats

A high-water alarm float is normally installed above the pump’s regular operating level.

Its purpose is not usually to control the main pump. Instead, it activates an audible alarm, warning light or remote notification when the water rises too high.

A high-water condition may indicate:

• A failed pump

• A stuck float switch

• A blocked discharge pipe

• A tripped breaker

• A failed check valve

• A frozen discharge line

• Water entering faster than the pump can remove it

High-water alarms are especially valuable in:

• Sewage basins

• Septic pump chambers

• Basement sump pits

• Seasonal properties

• Rural homes

• Cottages and camps

The alarm float should be installed high enough that normal pump operation does not activate it, but low enough to provide warning before the basin overflows.

7. Electronic Water-Level Switches

Electronic switches use sensors to detect the presence or level of water instead of relying entirely on a moving float.

Some electronic switches use metal probes, pressure sensors or solid-state controls.

Possible advantages include:

• No swinging tether

• Compact installation

• Fewer moving parts

• Less chance of becoming caught on piping

• Adjustable water levels on some models

• Useful operation in confined spaces

Electronic switches are available for sump pumps, utility pumps, water tanks and other applications.

However, the switch must be compatible with the pump’s voltage, amperage and intended use.

Mineral buildup, dirty water and electrical interference may also affect certain types of electronic sensors.

Piggyback Float Switches

A piggyback float switch plugs directly into a standard electrical outlet. The pump then plugs into the back of the float-switch plug.

When the float activates, power is supplied to the pump.

Piggyback switches are common in residential sump-pump systems and other single-phase pump applications.

One advantage of this design is that the pump can usually be unplugged from the float switch and tested separately.

If the pump works when plugged directly into the outlet but does not operate through the float switch, the switch may be faulty.

Hardwired Float Switches

A hardwired float switch is connected directly to the pump circuit, relay, motor starter or control panel.

Hardwired switches are commonly found in:

• Septic systems

• Sewage systems

• Commercial pump systems

• Duplex pump panels

• Cistern controls

• High-water alarm systems

Hardwired float switches must be installed using the proper electrical components and wiring methods for the application.

Pump-Down Float Switches

A pump-down float switch starts the pump when the liquid rises and stops the pump after the liquid level has been lowered.

Pump-down operation is commonly used for:

• Sump pumps

• Sewage pumps

• Effluent pumps

• Septic pump chambers

• Drainage systems

• Dewatering applications

The pump removes water from the basin until the float reaches its lower shutoff position.

Pump-Up Float Switches

A pump-up float switch works in the opposite direction.

It starts the pump when the liquid level becomes too low and stops the pump after the tank has been refilled.

Pump-up operation may be used for:

• Cistern filling

• Livestock water tanks

• Water-storage tanks

• Process tanks

• Rural water systems

• Lake-water systems

A pump-up float and a pump-down float may look almost identical, but they perform opposite functions.

The intended operation must always be confirmed before the switch is installed.

Normally Open and Normally Closed Floats

Float switches may also be described as normally open or normally closed.

A normally open float has an open electrical circuit while resting in its normal position. When the float moves to the activation position, the circuit closes.

A normally closed float works in the opposite way. The circuit remains closed in its normal position and opens when the float activates.

The correct option depends on whether the float is controlling a pump, alarm, low-water shutdown or high-level warning.

Common Signs of a Float-Switch Problem

A float switch may need to be adjusted, cleaned or replaced when:

• The pump does not start as the water rises

• The pump continues running after the basin is empty

• The pump starts and stops every few seconds

• The float must be moved manually before the pump starts

• The pump works when plugged directly into the outlet but not through the switch

• The float is caught against the pump or basin wall

• The high-water alarm keeps activating

• The switch works intermittently

• The pump runs but the water level continues rising

A float-switch problem can sometimes be caused by incorrect positioning rather than complete switch failure.

The float may not have enough room to travel, the tether may be too short or the switch may be mounted at the wrong height.

What Causes a Pump to Short Cycle?

Short cycling occurs when a pump starts and stops too frequently.

This can happen when:

• The float’s operating range is too small

• The sump pit is undersized

• Water is entering the basin very quickly

• The float is mounted too close to the pump

• The pump is oversized for the basin

• The check valve is leaking

• Water from the discharge pipe is flowing back into the pit

A wider operating range may allow the pump to run longer and reduce the total number of starts.

However, the correct float-switch setup depends on the size of the basin, pump capacity and amount of incoming water.

Choosing the Right Float Switch

The correct float switch depends on several factors, including:

• Pump voltage

• Pump amperage

• Pump horsepower

• Basin diameter and depth

• Required start and stop levels

• Available movement space

• Water, sewage or effluent application

• Solids and debris in the liquid

• Pump-up or pump-down operation

• Normally open or normally closed operation

• Piggyback or hardwired connection

• Direct pump control or control-panel signalling

• Potable-water approval

A switch designed for sewage or wastewater is not automatically suitable for use in a drinking-water tank.

Float switches used in potable-water systems should be specifically approved for that application.

Float-Switch Installation and Pump Service in Thunder Bay

A float switch is one of the most important components in an automatic pumping system.

Even a high-quality pump cannot protect a basement, empty a sewage basin or maintain a storage tank if its float switch is incorrectly selected, obstructed or improperly adjusted.

Superior Water & Wells provides pump-system troubleshooting, float-switch replacement, sump-pump solutions, sewage and effluent pump service, high-water alarms and rural water-system support throughout Thunder Bay and the surrounding area.

We serve rural homeowners, camps, cottages and lakefront properties throughout Shuniah, Neebing, Kakabeka Falls, Murillo, O’Connor, Nolalu, Pass Lake and the Highway 61 corridor.

Experiencing a pump that will not start, will not shut off or keeps short cycling?

Contact Superior Water & Wells for reliable pump and rural water-system service.

Superior Water & Wells — Rural Water Done Right.