Short answer: a compact float switch is a small, close-coupled water level switch built onto the side of a pump, rather than the large tethered float that hangs off a cable. It lets a pump run automatically in narrow sumps, shallow pits and tight corners where a standard float has no room to swing, and it switches off at a much lower water level.
On the APP pumps we supply, the compact float switch turns the pump on at around 30mm to 60mm of water and off again at 3mm to 25mm, depending on the model.
If you have ever bought an automatic pump for a small sump and found the float jammed against the wall of the chamber, you already understand the problem. Most automatic submersible pumps use a large pendant float on a length of cable. It needs space to rise and fall freely, and it needs a fair depth of water to work at all.
In a narrow sump, a shallow pit, a lift shaft base, or behind a flood barrier in a doorway, that space simply does not exist. A compact float switch solves it.
This guide explains what a compact float switch is, how it differs from a standard float, and which of the three APP models is right for your situation.
What is a compact float switch?
A compact float switch is a sealed level switch mounted directly onto the pump body, usually in a slim vertical guide or a small housing on the side of the casing.
Water rises, the float rises inside its guide, and the pump starts. Water drops, the float falls, and the pump stops. The principle is the same as any float switch. The difference is the size of the swing and the volume of water needed to trigger it.
Compact float switch vs standard pendant float
| Feature | Compact float switch | Standard pendant float |
|---|---|---|
| Space needed | Fits within the pump footprint | Needs 300mm or more of clear swing |
| Typical switch-on level | 30mm to 60mm | Often 200mm or more |
| Typical switch-off level | 3mm to 25mm | Often 100mm or more |
| Risk of jamming | Low, the float is guided and protected | Higher in small or cluttered chambers |
| Best for | Narrow sumps or recesses | Deep sumps and tanks |
When should you use a pump with a compact float switch?
A compact float switch earns its place whenever the water is shallow, the space is tight, or nobody will be there to press a switch.
- Narrow sumps and small pits, particularly retrofits into existing chambers
- Shallow water that needs clearing to a low level rather than a set depth
- Lift shaft bases, service pits and inspection chambers
- Behind a flood barrier, where seepage collects in a doorway recess
- Cellars, cupboards and plant rooms that flood occasionally and unpredictably
- Unattended buildings and outbuildings
If your chamber is deep and roomy, a conventional automatic pump is usually perfectly adequate. Compact float switches are about access and low level control. For more background on shallow water pumping, see our guide to what a puddle pump is and why you might need one.
The three APP compact float switch pumps compared
All three are 230V, plug in to a domestic socket, come with a 10m heavy duty rubber cable, and carry a 2 year warranty. The differences are size, flow and how dirty the water can be.
| Model | BPS100EA | RS32EA | RS40EA |
|---|---|---|---|
| Max flow | 70 l/min | 130 l/min | 200 l/min |
| Max head | 6.5m | 7m | 8.5m |
| Power | 0.10kW | 0.20kW | 0.25kW |
| Outlet | 19 and 25mm | 32mm | 32mm |
| Free passage | 3mm | 4mm | 7mm |
| Switches on at | approx 30mm | 50mm | 60mm |
| Switches off at | approx 3mm | 25mm | 20mm |
| Width | 134mm | 160mm | 168mm |
| Weight | 2.1kg | 3.9kg | 4.6kg |
APP BPS100EA: the smallest and lowest
At 134mm wide and 2.1kg, the BPS100EA is the pump for spaces where nothing else fits. It also has the lowest switch-off level of the three, stopping at around 3mm, so it leaves very little water behind.
APP RS32EA: the everyday choice
The RS32EA is the model most homeowners end up with. 130 l/min through a 32mm outlet handles a real ingress problem, and the slim body still drops into a narrow sump.
It switches off at 25mm, so it will not scrape a floor dry, but it will keep a chamber under control all day without anyone watching it. We used one to protect a doorway in this case study.
APP RS40EA: more flow and dirtier water
The RS40EA is the one to pick when the water arrives quickly or carries grit. 200 l/min and a 7mm free passage are a big step up from the smaller models, and it still switches off at 20mm.
If you are choosing between the RS32EA and the RS40EA, the free passage usually decides it. Silty cellar water is fine for either. Gritty water off a yard or a construction slab is better suited to the RS40EA.
Common mistakes when choosing a compact float switch pump
- Assuming automatic means it clears the floor. An automatic pump stops at its switch-off level. If you need a floor taken down to 1mm, you need a manual puddle pump or a sensor pump, not a float.
- Ignoring the free passage. A 3mm or 4mm free passage will block on leaf litter and coarse grit. Match the pump to the water.
- Buying on flow alone. A pump that does not physically fit the chamber is no use at any flow rate.
- Forgetting the hose run. Flow figures are quoted at zero head. Lift and hose length both reduce output, as we explain in our guide to pump head and friction loss.
- No non-return valve. Without one, water in the hose runs back into the sump each time the pump stops and the pump short cycles. More on that in why a puddle pump seems to stop working in shallow water.
Setting one up properly
A note on electrical safety: these pumps are supplied on a 230V plug. Use an RCD protected socket, keep the plug and any extension lead out of the water, and never lift or lower a running pump by its cable.
Frequently asked questions
Is a compact float switch as reliable as a standard float?
Yes, and in a small chamber it is usually more reliable, because there is far less chance of the float catching on a wall, a pipe or debris.
Can I fit a compact float switch to a pump I already own?
No. Compact float switches are built into the pump casing, so they come as part of the pump. If you want to automate an existing manual pump, use a separate level control panel instead.
How low will a compact float switch pump go?
Between 3mm and 25mm depending on the model. The BPS100EA is the lowest at around 3mm. If you need a floor genuinely dry, finish the job with a manual puddle pump.
Will it handle dirty water?
Lightly silted water, yes. Check the free passage figure: 3mm on the BPS100EA, 4mm on the RS32EA, 7mm on the RS40EA. None of them are sewage pumps.
Do I still need a non-return valve?
The RS32EA and RS40EA include an anti-airlock non-return valve device. On longer or steeper hose runs an additional inline non-return valve is still worth fitting to stop water draining back.
Conclusion
A compact float switch is what makes automatic pumping possible in the awkward places: narrow sumps, shallow pits, doorway recesses and small chambers where a pendant float cannot swing.
Choose the BPS100EA when access is the problem and the water is a trickle. Choose the RS32EA for everyday narrow sump duty. Choose the RS40EA when there is more water, or grittier water, to move.
