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Compact float switch for low and high liquid level testing with sealed reed relay (SPST) offering NO and NC operation.

(1-5: £7.79 each, 5+: £7.59 each)

FLOAT SWITCH. Compact float switch for low and high liquid level testing with sealed reed relay (SPST) offering NO and NC operation

Additional Information

NEW This compact float switch can be used at the top or bottom (remaining submerged) of a water tank for both high or low level sensing. A float mounted magnet moves up and down according to the level of water in the tank triggering a sealed reed relay.

Float Switch Configuration

The reed relay switch output can be set to normally open (NO) or normally closed (NC) simply by rotating the sensor through 180 degrees making it easy to put together systems which turn on/off when water reaches up to a certain level (float rising), or turn on/off when water falls below a certain level (float falling).

Below is an image of the float switch set up so that the relay switch is closed when the water level is high, and open when the water level is low:

If the whole float switch unit is rotated through 180 degrees (as shown below), the opposite happens – i.e. relay switch is closed when the water level is low, and open when the water level is high.


Installing the Float Switch

This float switch can be fitted in one of two ways. The first way is to drill a hole (approx 17mm diameter) through the side of the liquid tank, pushing the float switch through, and then sealing everything up using the supplied push-on rubber O-ring. Additional sealant (e.g. silicon) can be used around the opening on both sides of the tank to keep everything leak free.

Installing a float switch through the side of a tank

Alternatively, the whole unit can be glued to the side of a tank using an appropriate waterproof adhesive. It must be stuck on very well so that just the float part of the float switch floats.

Technical Specification

The reed relay is in single pole single throw (SPST) configuration. It is rated to switch currents up to a maximum of 1 Amp, at voltages of up to 100VDC or 250VAC. Contacts are rated at 15 Watts.

The float switch body is made from acetal copolymer and the float from foamed polypropyline. The overall length is 85.5mm, with a 15.5mm diameter float. 10cm flying leads are fitted to the float switch for easy connection into your system.

The operating temperature of this float switch is -30 to +60 degrees Celcius, so it is not suitable for use with most solar water heating systems (which can generate temperatures of 85+ degrees C).

For low level sensing, the sealing of this float switch is rated at 5 psi pressure (0.34 bar) equivalent to a maximum depth of around 2-3 metres in water. Therefore, this float switch could be used at the bottom of a 2-3 metre deep tank to detect when there is no liquid left.

The liquid in the tank in which the float switch is to be used must have a specific gravity* of 0.8 or more.
* The specific gravity (SG) of pure water is approximately 1.00 and of seawater 1.03, so this a float switch can be used. Olive oil has an SG of 0.7, and gasoline (petrol) of 0.74, so a float switch cannot be used – basically because the float cannot float on liquids which have densities 80% or lower than that of water.

Alternative Products

Our Liquid Sensor can be used as an alternative to this float switch.