In compact water tanks and automated water replenishment systems, achieving reliable multi-point liquid level detection can be challenging. Limited installation space, closely spaced switching points, and the need for independent level signals require careful mechanical and electrical design.
Recently, the Équipe d'ingénierie ELECALL developed a customized multi-point liquid level control solution for a South American customer. The application required a compact PP plastic multi-point float level switch capable of providing multiple independent liquid-level signals within a reservoir approximately 200 mm high.
Based on the tank dimensions, target liquid levels, control logic, and installation requirements, ELECALL developed a customized EP20010-5 multi-point PP float level switch and prepared a corresponding technical drawing.
This case demonstrates how a customized multi-point float switch can provide compact installation, independent level detection, automatic pump control, and reliable liquid-level monitoring in a small water reservoir.
Customer Application and Requirements
The customer was developing an automated water replenishment system for a compact water reservoir.
The approximate reservoir dimensions were:
- Height: 200 mm
- Length: 150 mm
- Width/Depth: 60 mm
- Maximum geometric capacity: approximately 1,800 mL
The customer required multiple independent liquid-level detection points so that the control system could monitor different water levels and stop the filling pump when the selected level was reached.
The initial four-float requirement specified approximate liquid levels of:
| Float | Approx. Liquid Level | Approx. Water Volume | Intended Function |
|---|---|---|---|
| Float 1 | 30 mm | 270 mL | First level control |
| Float 2 | 60 mm | 540 mL | Second level control |
| Float 3 | 120 mm | 1,080 mL | Third level control |
| Float 4 | 180 mm | 1,620 mL | Main operating level |
The customer also asked whether a fifth float could be added above the normal operating level as an additional high-level safety switch.
The preferred electrical configuration was Normally Closed (NC).
When the liquid level remained below the corresponding switching point, the contact would remain closed. When the liquid reached the selected level, the float would rise and cause the corresponding reed switch contact to open.
The float level switch would not directly power the pump. Instead, it would provide a low-current signal to a relay, MOSFET, PLC, or controller, which would then control the filling pump.
From Customer Requirements to an Engineered Solution
The customer’s initial requirements provided the target liquid levels, but the final product configuration required additional mechanical consideration.
For a multi-float level switch, the actual float positions cannot be determined only by the desired liquid volumes. The engineering design must also consider:
- Float dimensions
- Float travel
- Circlip positions
- Distance between adjacent floats
- Reed switch operating characteristics
- Overall rod length
- Available tank height
- Potential interference between adjacent floats
After reviewing these factors, the ELECALL engineering team developed a customized positioning arrangement for the EP20010-5.
According to the ELECALL technical drawing, the defined positions are:
- 30 mm: lower circlip position
- 60 mm: Float 1 position
- 120 mm: Float 2 position
- 150 mm: Float 3 position
- 170 mm: Float 4 position
- 200 mm: upper positioning limit
This configuration is different from simply reproducing the customer’s initial requested 30 mm, 60 mm, 120 mm, and 180 mm level points.
Instead, ELECALL optimized the mechanical positioning arrangement according to the actual structure, available installation space, and operating range of the multi-float assembly.
Le 30 mm and 200 mm positions define the mechanical boundaries, while the 60 mm, 120 mm, 150 mm, and 170 mm positions correspond to the four independently positioned floats.
Customized EP20010-5 Multi-Point PP Float Level Switch
Based on the application requirements, ELECALL recommended a customized EP20010-5 multi-point PP plastic float level switch.
The vertical structure integrates multiple floats and corresponding magnetic reed switches into one compact level detection assembly.
Main Structural Configuration
| Paramètre | Spécification |
|---|---|
| Modèle | EP20010-5 |
| Float Quantity | 4 |
| Float Material | PP |
| Main Rod Material | PP |
| Main Rod Diameter | Ø8 mm |
| Float Diameter | Ø24 mm |
| Float Height | Approx. 20 mm |
| Overall Rod Length | Approx. 200 mm |
| Mounting Thread | M10 × 1.5 |
| Thread Length | Approx. 13 mm |
| Sensing Element | Magnetic reed switch |
| Contact Logic | Normally Closed (NC) |
| Wiring | 5 wires |
| Signal Output | 4 independent signals + 1 common wire |
The compact vertical structure allows multiple liquid-level detection points to be integrated into one assembly, educing the need for several separate float switches inside the reservoir.
PP Float Material: Lightweight, Cost-Effective, and Resistant to Mild Corrosion
A key feature of this solution is the use of PP (Polypropylene) floats.
PP is a lightweight engineering plastic with a relatively low density compared with metals. This makes it particularly suitable for float switches because the float can remain lightweight while providing sufficient buoyancy for movement with the liquid level.
Low Density for Reliable Float Movement
The relatively low density of PP helps create a lightweight float structure.
A lightweight float requires less buoyant force to move, which can contribute to smooth movement along the guide rod. This is particularly useful in compact multi-float assemblies where several floats are installed on the same rod.
Reducing unnecessary moving mass can also help maintain stable float movement within a limited installation space.
Cost-Effective for OEM Applications
PP is generally more economical than stainless steel and other metal materials.
For OEM equipment and volume-production applications, PP floats provide a practical balance between functionality, durability, and manufacturing cost.
This makes them suitable for applications such as:
- Réservoirs d'eau
- Systèmes de réapprovisionnement automatique en eau
- équipement de traitement de l'eau
- Household and commercial equipment
- General liquid-level control
- Cost-sensitive OEM applications
Resistance to Water and Mildly Corrosive Liquids
PP offers good resistance to water and many common chemicals and is suitable for water and mildly corrosive liquid environments.
This allows PP floats to be used in many general liquid-level applications where exposure to moisture or mild chemical environments is expected.
For aggressive chemicals, high concentrations, or elevated temperatures, material compatibility should be evaluated according to the specific liquid and operating conditions.
Lightweight and Compact
The lightweight PP construction also helps reduce the moving mass of the float.
Combined with the compact Ø24 mm float size, this makes the design suitable for narrow reservoirs where installation space is limited.
Multi-Point Float Positioning
One of the most important engineering challenges in this application was determining the actual mechanical positions of the floats.
The ELECALL engineering drawing defines the following positions:
| Position | Fonction |
|---|---|
| 30 mm | Lower circlip / lower mechanical limit |
| 60 mm | Float 1 |
| 120 mm | Float 2 |
| 150 mm | Float 3 |
| 170 mm | Float 4 |
| 200 mm | Upper positioning limit |
30 mm — Lower Circlip Position
The 30 mm position is used as the lower circlip position rather than as an independent liquid-level detection point.
The circlip serves as a mechanical position limiter, restricting the downward movement of the corresponding float and helping maintain the designed operating range.
60 mm — Float 1
The first independently positioned float is located at approximately 60 mm.
When the liquid level reaches the corresponding switching range, the float moves upward and activates the associated reed switch, providing the first independent liquid-level signal.
120 mm — Float 2
The second float is positioned at approximately 120 mm.
It provides a separate switching signal when the liquid reaches the corresponding level.
Based on the approximate tank dimensions, 120 mm represents a theoretical water volume of approximately 1,080 mL.
150 mm — Float 3
The third float is positioned at approximately 150 mm.
This additional switching point provides another independent liquid-level signal for the control system.
The 150 mm position also demonstrates that the final engineered configuration was optimized according to the actual multi-float structure rather than simply duplicating the customer’s initial requested level.
170 mm — Float 4
The fourth float is positioned at approximately 170 mm.
This provides the highest regular switching point in the customized four-float arrangement.
It can be used as a high operating-level signal or as part of the customer’s programmed pump-control sequence.
200 mm — Upper Positioning Limit
The 200 mm position defines the upper positioning limit of the assembly and corresponds approximately to the overall height of the reservoir.
Together with the lower circlip, this provides a defined mechanical range for the multi-float structure.
Relationship Between Liquid Level and Water Volume
The customer’s reservoir dimensions were approximately 150 mm × 60 mm.
Assuming a relatively uniform cross-section, the horizontal area is approximately:
150 mm × 60 mm = 9,000 mm²
The theoretical water volume at different liquid heights can therefore be estimated as follows:
| Liquid Height | Theoretical Volume |
|---|---|
| 30 mm | Approx. 270 mL |
| 60 mm | Approx. 540 mL |
| 120 mm | Approx. 1,080 mL |
| 150 mm | Approx. 1,350 mL |
| 170 mm | Approx. 1,530 mL |
| 180 mm | Approx. 1,620 mL |
| 200 mm | Approx. 1,800 mL |
These values provide a useful reference for understanding the relationship between liquid height and reservoir volume.
However, the actual switching level should be determined according to the final mechanical position of the float and the operating characteristics of the reed switch, rather than assuming that the float’s physical position directly equals the liquid surface height.
Actual usable capacity may also vary because of the reservoir’s internal structure, rounded corners, fittings, and other components.
Upward Float Movement and Normally Closed (NC) Operating Logic
The EP20010-5 operates based on the natural movement of the floats with the liquid level.
As the water level rises, each corresponding float moves upward along the guide rod. When the float reaches the operating range of its magnetic reed switch, the contact changes state.
The basic operating principle is:
Liquid Level Rises → Float Moves Upward → Reed Switch Changes State → Control System Receives Signal
For the requested NC configuration:
Liquid Level Below Switching Point → Float Down → Contact Closed
Liquid Level Reaches Switching Point → Float Rises → Contact Opens
When the liquid level is below the corresponding switching point, the float remains in its lower position and the reed switch contact remains closed.
As the liquid rises, the float moves upward with the liquid surface. When the internal magnet reaches the effective operating range of the reed switch, the contact opens.
The control system can then detect this change and use a relay, MOSFET, PLC, or other control circuit to stop the filling pump.
Independent Signal Output and Five-Wire Configuration
Each float operates independently and provides a separate electrical switching signal.
For the customized four-float configuration, the level switch uses five wires in total:
- 4 individual signal wires — one for each float
- 1 common wire shared by all four floats
This configuration allows the external control system to identify the switching status of each float independently.
Par exemple:
- Float 1 → Signal 1
- Float 2 → Signal 2
- Float 3 → Signal 3
- Float 4 → Signal 4
- Common → Shared electrical connection
The individual signals can then be connected to a relay, MOSFET, PLC, or other controller according to the customer’s control requirements.
This makes the multi-point float switch suitable for applications requiring different pump-control levels, alarms, status monitoring, or programmed liquid-level sequences.
Why Use a Relay, MOSFET, or Controller?
The customer specified that the level switch would provide a low-current signal rather than directly powering the pump.
The recommended control architecture is:
Multi-Point Float Switch → Controller / Relay / MOSFET → Filling Pump
The float switch detects the liquid level and provides the corresponding switching signal.
The external control device then processes this signal and controls the pump.
This approach provides several benefits:
- Reduces the electrical load on the reed switch
- Separates sensing and power circuits
- Allows easier integration with electronic control boards
- Supports programmable pump-control logic
- Makes it easier to add alarms and safety interlocks
- Provides greater flexibility for OEM equipment design
The float switch therefore functions primarily as a liquid-level sensing component, while the external control circuit handles the pump’s operating current.
Electrical Characteristics
The final electrical parameters depend on the selected reed switch configuration and the customer’s control requirements.
| Paramètre | Spécification |
|---|---|
| Type de contact | Normally Closed (NC) |
| Sensing Element | Magnetic Reed Switch |
| Wiring | 5 wires |
| Signal Channels | 4 independent + 1 common |
| Maximum Switching Power | Up to 10 W / 50 W, depending on configuration |
| Tension de commutation maximale | Up to 100 V DC / 220 V AC, depending on configuration |
| Courant de commutation maximal | Up to 0.5 A |
| Recommended Control Voltage | 5–24 V DC |
| Sortir | Low-current switching signal |
| External Control | Relay / MOSFET / PLC / Controller |
The final electrical rating should always be confirmed according to the selected reed switch specification and the customer’s actual control circuit.
Circlip Position Limiters
The rings shown below the floats in the technical drawing are circlips.
Each circlip serves as a mechanical position limiter for the corresponding float. It restricts the downward movement of the float and helps maintain the designed operating range.
The position of each circlip is therefore an important part of the mechanical design.
The relationship between the float and circlip helps determine:
- The float’s available travel
- Its mechanical lower limit
- The relative position of adjacent floats
- The overall operating range of the assembly
For multi-float applications with limited vertical space, accurate mechanical positioning is particularly important to prevent interference between adjacent floats.
Float Positioning Accuracy and Reed Switch Tolerance
One important consideration in this project is the accuracy of the actual switching position.
Although the float and circlip positions can be customized according to the customer’s required dimensions, achieving an absolutely precise switching point to the millimeter is difficult.
A typical operating-position deviation of approximately 3–4 mm should normally be expected.
This tolerance is not primarily caused by the machining accuracy of the float switch. It is related to the operating characteristics and actuation range of the magnetic reed switch.
A reed switch is activated when the magnetic field reaches its effective operating range. Therefore, the actual switching point may vary slightly rather than occurring at one mathematically exact position.
For applications requiring precise liquid-volume control, an appropriate switching tolerance should therefore be considered during system design.
The customer should confirm whether an approximately 3–4 mm deviation is acceptable for the intended application.
Why ELECALL Recommended a Four-Float Configuration
The customer initially asked whether a fifth float could be added as an independent high-level safety switch.
During the engineering review, however, ELECALL identified a position conflict between the fourth and fifth floats.
Because the available internal height of the reservoir is limited to approximately 200 mm, adding another float would further reduce the available vertical operating space.
A multi-float switch requires sufficient travel for each float to move properly. If the floats are positioned too closely together, there is a greater possibility of mechanical interference or insufficient operating travel.
Therefore, considering the actual tank dimensions and the mechanical movement requirements, ELECALL did not recommend adding a fifth float to this particular application.
The four-float configuration provides a more practical arrangement within the available space and helps maintain reliable independent operation of each float.
This illustrates an important principle of customized engineering:
The best solution is not necessarily the configuration with the largest number of sensing points, but the configuration that provides reliable operation within the actual installation conditions.
Compact Design for Space-Limited Water Tanks
One of the main engineering challenges in this application was the limited space inside the reservoir.
With a tank height of approximately 200 mm and a width/depth of approximately 60 mm, installing several independent level sensors could increase mechanical complexity and require additional internal wiring.
The EP20010-5 integrates multiple switching points into one vertical assembly.
This provides several practical advantages:
- Multiple level signals from one compact assembly
- Reduced installation space
- Fewer individual sensors required
- Simplified internal wiring
- Independent switching points
- Customizable float positions
- Easy integration with external controllers
- Suitable for compact automated equipment
For OEM equipment manufacturers, an integrated multi-point design can also simplify assembly and reduce the number of components installed inside the reservoir.
Engineering Drawing and Custom Manufacturing
This project was not simply a matter of selecting a standard catalog product.
The ELECALL engineering team reviewed the customer’s:
- Reservoir dimensions
- Required liquid levels
- Target water volumes
- Number of floats
- Float movement range
- Circlip positions
- NC control logic
- Pump control method
- Installation limitations
Based on these requirements, ELECALL developed the customized mechanical configuration and prepared the corresponding technical drawing.
For multi-point float switches, accurate mechanical positioning is critical.
The positions of the circlips and floats determine the available movement range and switching behavior. Incorrect spacing could result in insufficient float travel or mechanical interference between adjacent floats.
Therefore, engineering drawings play an important role in confirming the final dimensions and configuration before production.
Final Customized Configuration
After evaluating the application requirements and mechanical limitations, the recommended configuration for this project was:
| Item | Final Configuration |
|---|---|
| Modèle | EP20010-5 |
| Float Quantity | 4 |
| Float Material | PP |
| Rod Material | PP |
| Float Diameter | Ø24 mm |
| Rod Diameter | Ø8 mm |
| Lower Circlip Position | 30 mm |
| Float 1 Position | 60 mm |
| Float 2 Position | 120 mm |
| Float 3 Position | 150 mm |
| Float 4 Position | 170 mm |
| Upper Positioning Limit | 200 mm |
| Mounting Thread | M10 × 1.5 |
| Wiring | 5 wires |
| Signal Configuration | 4 independent signals + 1 common |
| Contact Logic | Normally Closed (NC) |
| Positioning Tolerance | Approx. 3–4 mm |
| Recommended Configuration | 4-float |
This final configuration balances multi-point level detection, compact installation, mechanical reliability, and electrical integration within the limited space of the reservoir.
ELECALL Multi-Point Float Switch Customization
The EP20010-5 is not limited to one fixed configuration.
ELECALL can customize multi-point float level switches according to different equipment requirements.
Available customization options include:
- Number of floats
- Float positions
- Float spacing
- Circlip positions
- Rod length
- Mounting thread
- Float orientation
- longueur du câble
- Type de câble
- Normally Open (NO) or Normally Closed (NC) logic
- PP or stainless-steel construction
- Connector and wiring configuration
This allows the level switch to be designed around the customer’s actual tank dimensions and control requirements rather than forcing the equipment to adapt to a fixed standard sensor.
ELECALL can also provide technical drawings for customized configurations to help customers confirm dimensions, installation positions, and electrical connections before production.
Conclusion
This South American customer project demonstrates how a customized multi-point float level switch can address the challenge of multi-level liquid detection in a compact water reservoir.
Based on the customer’s approximately 200 mm-high reservoir, ELECALL developed a customized EP20010-5 PP multi-point float level switch with a defined mechanical arrangement of 30 mm, 60 mm, 120 mm, 150 mm, 170 mm, and 200 mm.
In this configuration, the 30 mm position serves as the lower circlip position, while the 60 mm, 120 mm, 150 mm, and 170 mm positions define the four independently positioned floats. The 200 mm position serves as the upper positioning limit of the assembly.
The solution combines a compact vertical structure with Normally Closed (NC) reed switch logic, allowing the level switch to provide four independent low-current signals through a 5-wire configuration: four individual signal wires and one common wire.
L'utilisation de Flotteurs PP provides a practical combination of low density, lightweight construction, cost efficiency, and resistance to water and mildly corrosive environments, making PP an attractive material for many general liquid-level control applications.
At the same time, the engineering evaluation showed why simply adding more floats is not always the best solution. Due to the limited tank height and potential position conflict between the fourth and fifth floats, ELECALL recommended a four-float configuration for this application.
More importantly, this project demonstrates ELECALL’s ability to provide more than a standard float switch. From float quantity and positioning to circlip locations, rod dimensions, electrical logic, cable configuration, positioning tolerance, and engineering drawings, ELECALL can develop application-specific liquid-level sensing solutions based on actual equipment requirements.
Learn More About the EP Series
Le ELECALL EP Series PP Plastic Float Level Switches provide compact and cost-effective solutions for water tanks, automatic water replenishment systems, water treatment equipment, household appliances, and general liquid-level control.
With options for different float configurations, materials, cable lengths, switching logic, and customized dimensions, the EP Series can be adapted to a wide range of OEM applications.
Explore the EP Series and find the right float level switch for your application.
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