Tag Archives: float switch

What is a submersible pump float switch and which type do I need?

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.

Mac-3 Pendant type Float SwitchA 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.

Operation of a pendant type float switch in a sump

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

JS-250 Submerisble Pump with Mac-3 Pendant Float SwitchThe 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

RS-150 Submersible Pump with Agma Magnetic Tube Float SwitchThe 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.

How to Keep Your Cellar or Basement Dry

One of our most frequently asked questions is “what’s best pump to deal with cellars/basements that periodically get flooded out?” Typically, the flooding occurs after heavy rainfall, if the water table is high or if you live in close proximity to a river/lake. The solution is a submersible pump.

Submersible Pumps

Pedrollo TOP Submersible PumpFor this type of application, we would normally recommend a submersible pump – a small electric pump, which can be completely (or partially) submerged underwater. The pump sucks the water through a strainer in its base and pumps it from the outlet (normally located on the top of the pump) through a hose to a suitable discharge point (the nearest drain or similar).

For ease of use, most submersible pumps are available with a float switch (it’s the round, black and orange part of the pump in the photo) – this a similar to a ballcock in a toilet cistern – when water is present it floats up and turns the pump on, when the water has drained away the float drops down and turns the pump off. This allows for automatic operation, meaning the user doesn’t have to manually turn the pump on and off when the water rises. However, submersible pumps with float switches work best when installed in a sump (essentially a hole dug in the floor) and need to be of a suitable size to allow the float switch to move freely (typically around 400 mm x 400 mm x 400 mm). They will usually only drain water down to a level of a few inches.

Puddle Pumps

RS-Pumps RSD-400 Submersible Puddle PumpIf you prefer not to dig a sump, we can offer an alternative – a puddle pump. These low-level drainage pumps are engineered to pump water from flat surfaces down to around 1 mm deep (hence the name!), and are ideal for cellars, basements, car parks and flat roofs.

Due to their low-level performance, puddle pumps are not supplied with a float switch and as such are normally manually operated.

For fixed installations, such as keeping your cellar/basement dry, we would recommend using an automatic control panel which uses a sensor to detect the presence of water and operate the pump.

For other applications, such as drainage of persistent nuisance water from areas such as flat roofs and car-parks  puddle pumps are best manually operated and can be used like a vacuum cleaner to “hoover” up the water – you can even sweep the water into the pump to help it drain away!

Our Submersible Pump Recommendation

Our most popular submersible pump for domestic drainage is the Pedrollo TOP range, these lightweight yet robust pumps are available in a number of different sizes, each offering improved performance (the bigger the electric motor, the faster is will drain the water away).

Pedrollo also offer a puddle pump, the TOP Floor which drains down to 2-3mm, but our most popular model is the JS-Pumps RSD-400. This stainless steel-bodied pump provides excellent performance and superior low-level drainage.

What is the difference between a Puddle Pump and a Submersible Pump?

A submersible pump is usually a small electric pump used for drainage duties. As the name implies, the whole pump can be submerged under water – in most cases this is necessary to keep the electric motor cool and prevent overheating.

Submersible Pumps

Submersible pumps can be manually or automatically operated. Manual pumps require the user to switch the pump on when required and off when the water has drained away (dry-running of a submersible pump will normally cause damage to its internals). Automatically operated pumps have a float switch (similar to a ball-cock in a toilet cistern) which switches the pump on and off at pre-set water levels. Submersible pumps with float switches usually require a certain amount of space around the float for it to operate and these work best in tanks or for drainage of cellars/basements in a sump (essentially a hole dug into the floor where water collects).

Submersible pumps will typically drain water down to a level of approximately 30 mm.

A popular example of a domestic-use submersible pump is the Pedrollo TOP range – you can see in the diagram below a typical installation in a sump, with sufficient space for the float to operate unobstructed.

Pedrollo TOP Submersible Pump installation in a sump

Puddle Pumps / Puddle Suckers

Puddle Pumps (also known as Puddle Suckers) are submersible pumps with the ability to drain down to very low levels (typically as low as  1mm, and so can be fully or partially submerged). They are usually manually operated (no float switch) and are ideal for draining water from flat surfaces such as roofs, car-parks and cellars.

Puddle Pump in Cellar

Automatic operation is an option for some puddle pumps in fixed installations through the use of a capacitive water sensor and control unit.


A Puddle Pump is really just a type of submersible pump with a specifically designed impeller and strainer to allow for low-level drainage applications on flat surfaces.

Our two best-selling puddle pumps are the Pedrollo TOP Floor, which pumps down to 2mm and is ideal for domestic drainage duties, and the RSD-400 Puddle Pump, a higher performance pump which drains down to 1mm and due to its stainless steel construction is suitable for domestic and on-site drainage.

See our full range of submersible pumps.