When researching which submersible pump to buy, you will inevitably see pumps which are available with numerous types of float switch, here we’ll describe their operation and two of the most common types.
A float switch is a mechanism used to detect the level of water around a submersible pump, allowing the pump to operate automatically – when the water reaches a certain pre-set depth the float switch will trigger the pump to switch on and start pumping. When the water level drops below another pre-set level, the pump will then be turned off automatically and stops pumping.
This automatic operation ensures that the pump will never “run-dry”. The electric motor in a submersible pump is normally water cooled – the action of pumping the water through the pump body keeps the electric motor within normal operating temperatures – when there is no water present, the pump could run-dry and overheat, cause damage to the motor.
The submersible pumps we stock can be supplied with a float switch for automatic operation, or without a float switch for manual operation.
For most of our pump range, there are two options for the type of float switch: a free-moving float attached to the pump via an electrical cable, or a tube float which is normally mounted on the side of the submersible pump.
Free-Moving Pendant type Float Switch
The standard option is the free-moving pendant float – these are generally manufactured from tough polypropylene plastic with a micro-switch mechanism inside. When there is sufficient depth of water the air-filled bulb will float upwards, triggering the micro-switch to power up the pump. When the water has been pumped away and the level decreases, the float will drop, switching the pump off again. This type of float switch generally requires the submersible pump to be installed in a tank or sump and needs approximately 300 mm of space around the pump to operate properly. This ensures the float doesn’t get snagged or tangled on the sump or tank walls.
Tube-type Magnetic Float Switch
The second option is the tube-type, or magnetic float switch. This is close-coupled to the pump body and has a float which slides vertically inside a tube – when the float is at the top of the tube, a micro-switch turns the pump on and when the float drops to the bottom, the pump is switched off. This type of float switch is ideal for installing pumps is space-limited areas, where a standard float switch wouldn’t have room to operate.
When purchasing a submersible pump keep in mind the intended use: a manual submersible pump will require you to switch it on and off when required. A submersible pump with a tube type float is ideal for automatic operation in small sumps, and the standard bulb, free-moving pendant float switch is suitable for most other applications requiring an automatic operation.