Float switch: what is needed and what to consider when choosing and installing

Amir Gumarov
Checked by a specialist: Amir Gumarov
Author: Natalya Listyeva
Last update: May 2019

Reliable, practical and convenient float switch ensures the correct automatic adjustment of the electric pumps in sewer, drainage, drainage and water supply systems, acts as a water level sensor and protects the equipment from "dry running".

A properly connected device monitors the functioning of communication elements and turns on or off the pump when the permissible level of water or other liquid in the system changes. It is located in various storage tanks, containers, tanks, wells, etc.

Construction device and unit capabilities

The float switch has an elementary design. Inside the case, made of durable heat-resistant plastic, there is a working electrical switch. There is also a lever for transferring contacts in the switch and a steel ball that changes the position of the lever element when changing the position of the float itself.

Devices of this type belong to the universal variants of household equipment, because they work equally correctly both in case of overflow and when the storage tank is empty.

The interior view of the float
Despite the structural simplicity, the float switch demonstrates high efficiency and can simultaneously solve several tasks at once. The presence of this device greatly facilitates the management of equipment and extends its full, high-quality functioning

A cable consisting of three wires — blue, brown, and black — branches off from the switching unit. One of them (black) is common, brown comes from a normally closed, and blue - from a normally open switch contacts.

Float switch operation diagram
When the float in the tank is in the lower position, the circuit closes between the blue and black wires. If the device moves to the upper position, the contacts between the brown and black elements are closed. In each individual case, a wire that is not involved in the wiring diagram must be reliably and efficiently insulated

The supply cable and housing box are also subject to special requirements. The first element is simply required to have the highest level of moisture resistance, and the second part must be completely tight and impervious to water.

The outlet of the device is strengthened by an additional high-strength sealant and is equipped with a practical device that provides neutralization of mechanical stresses in the cable.

Pump float switch
A float switch protects the pump against idling when the accumulated liquid is almost completely pumped out of the tank

The insulated hollow portion of the cable entry is filled with polymer resin. This eliminates the ingress of moisture or any other liquid in which the equipment operates.

The case and cable sheath are highly durable and heat resistant. Due to this, they are practically immune to the effects of elements of an aggressive environment such as liquid oils, fecal water, uric and fruit acid, gasoline, etc.

Float switches of different sizes
For more precise control of the pump in the communication system, several float switches can be placed inside the liquid tank. Each of them will perform a specific function and greatly facilitate the operation of equipment

The interior of the circuit breaker housing is filled with air. Therefore, the device seeks to surface and occupy the highest possible position. When the liquid level in the tank drops, the float naturally falls down.

The length of the wire provided for moving the mechanism controls the spread between the upper and lower positions of the float. The basic starting point, relative to which the movement is carried out, sets the load moving along the cable of the switch.

The plastic case has a smooth, non-porous surface. Pollution does not stick to it and fragments of human waste that do not adhere to sewage or sewage.

Sand, paper and any other solid or dense pieces and elements slide off the unit, without affecting its performance, buoyancy and functionality.

Float switches are multifunctional and capable of solving a whole range of tasks of different difficulty levels.

Only a few modules mounted in one tank provide:

  • efficient operation of the main pump of the communication system;
  • full operation of the auxiliary pump.

In addition, they can play the role of an emergency controller, clearly fixing a sharp decrease in the liquid level in the tank and act as a sensor-signaling overflow.

Drain pump with float switch
A drainage pump equipped with a float switch will help during the snow melt or in the rainy season to drain the area adjacent to the household or pump out water from the pool for scheduled cleaning and further full operation

This will make it possible to reduce the load on the equipment and protect pumping system from excessive wear, the transition to a “dry run” and other unpleasant, but potentially possible incidents.

General device classification

Modern float switches are divided into two types. Lightweight modules are intended for pumping complexes that carry out the diversion or supply of consumers with running water for domestic purposes. Heavy appliances are used to control drainage and fecal pumping equipment.

Pump with float switch in operation
How many floats to place in the tank is determined separately in each individual case, and directly depends on the number of connected pumps and the total need of the system for safety units

You need to buy a float switch for the pump with a clear understanding of the tasks that need to be solved. Light elements attract customers at a low price, but can only work in clean water intended for drinking and domestic needs.

Heavy aggregates function effectively in an environment of any level of aggressiveness, however, it is considered impractical to use them for ordinary water because of the high cost.

Terms of making a correct purchase

Before buying a float warning device, it is necessary to indicate the area and method of application of the equipment, the necessary electrical characteristics, module dimensions and cable length.

Float switch
When an old-style pump, not equipped with a switch, is used in communications, there is always a risk that the equipment may fail due to a sudden excessive load

To avoid troubles, you should separately purchase a float element and connect it to the system with your own hands or by calling a professional at home.

If a float is planned to equip a drainage or water intake system, it will be enough to purchase an inexpensive module of a light type. It has good swimming ability, clearly responds to the water level in the tank and immediately gives a signal to other elements of the system if any changes suddenly occur.

For drainage and sewer systems, heavy floats without a sinker, designed to be in an aggressive environment of high density, are suitable.

Electrical Features

The current and voltage of the float switch must clearly correspond to the parameters of the electric pump. The voltage level, as a rule, is 220 V. Fluctuations of this indicator are permissible in the range of 5-10%, both up and down.

As for the current strength, this value at the switch must exceed the parameters prescribed for the pump. In the documentation of the float, the maximum permissible indicator for reactive and active loads is usually written. When connecting pumping equipment, the number corresponding to the reactive position is usually taken into account.

Additional selection criteria

The temperature range of float switches is quite large. Due to this, for water intake from a well or well pumping station you can choose any unit that is most suitable for the tasks in all other parameters.

Float switch
The average temperature range for floats is 0-60 ℃. However, some manufacturers produce even more heat-resistant modules that can withstand temperatures up to + 70 ℃

But the size of the outgoing connecting cable will have to pay special attention. Usually the length of this element is from 2 to 10 meters. Devices with a short wire are more suitable for shallow reservoirs, and parts equipped with a long cable will successfully work in wells and modern storage tanks great depth.

Features of the installation of the float

There are several ways to correctly install a float switch. Before starting work, first of all, you need to make sure that the current consumed by the pump is less than the maximum allowable current indicator prescribed in the equipment operation documents.

Easy installation for one module

The simplest, fastest and not too laborious installation method is to install the float in the tank using a waterproof cable and a special sinker, which is usually included in the basic unit kit.

Installation work is carried out in the following order:

  1. A sinker is strung on a cable cable.Then, by experiment, the shoulder length of the freewheel of the float device is determined.
  2. Then the position of the sinker is fixed on the cable using a special practical latch.
  3. The cable is attached to the outside of the tank by means of connecting elements.
  4. When the preparatory work is done, the float is connected to the pumping system. Installation and adjustment of equipment is carried out according to the schemes contained in the documentation attached to the device.

At the end of all necessary actions, the equipment must be tested for operability. To do this, the pump under the control of the hosts starts in normal mode for 2-3 hours.

Tank float switch
Mounting the float switch on the supply cable is permissible only when only one such unit will operate in the tank. There should also be no prerequisites for the device to catch on something or freeze inside the container

If the water pumping is normal and does not fail, then the installation and subsequent connection were made in compliance with all the rules.

Rules for the installation of two or more products

If according to the design documentation it is required to install several float devices, it makes sense to use a bar-mounted installation method. A fragment of a strong plastic pipe is suitable for the role of a fastener (rod). It is clearly and reliably fixed inside the container intended for filling.

Then, the floats are mounted on the rod base. They are evenly distributed along the entire length of the pipe so that after fixing and adjusting, there is free space around each module, which allows the devices to clearly perform their functions without interfering with each other.

The cables extending from the switches are attached to the boom using clamps. This method allows you to install almost any number of switches, thus taking control of a full-fledged complex, consisting of several pumps.

If necessary, it is permissible to use two or more rods and mount the necessary number of floats on them, corresponding to the number of pumps or control panels used.

The principle of operation of the float in different systems

The scope of float switches is very wide. The element functions correctly in standard water supply systems, effectively controls the filling and emptying of the capacity of the storage tank of the tank, protects the equipment from idling and extends its life.

The role of the switch in water supply complexes

A device placed in a container floats to the surface when the tank is filled with water, and timely shuts off the existing pump, preventing overflow in this way. When the water level drops, the float drops with it and immediately activates the pump for the subsequent filling of the tank with water.

Being on the surface of the tank (when the tank is full), the device will signal to work automatic water supply station and turn it off when it sinks to the bottom (with an empty tank).

Float switch pump
Many manufacturers of modern domestic pumps initially complete their products with a practical, convenient, high-strength, heat-resistant and waterproof floating switch. Having purchased such an aggregate, the owners will no longer have to pick up a float to it and mess with the correct connection of the device to the equipment pumping water

To close the valve or lower the valve with a servo-actuator, the float will command, being on the surface of a tank filled with liquid. Having sank to the bottom (with the tank empty), the device again opens the valve or gate valve, reactivating the filling of the tank with water.

A signal will be sent to the control room or directly to the operator when it is on the surface of a filled tank.The device will inform about the lack of water in the tank when it sinks to the bottom of the working tank.

Contact with drainage or sewage system

For drainagefecal and sewage pumps A heavy float switch is recommended. It is adapted to work in high-density fluids and easily copes with assigned tasks.

The device clearly monitors the operation of the pumping complex and, having emerged to the surface when the tank is full, immediately activates the equipment. Shutdown is carried out at that moment when the device sinks to the bottom as a result of emptying the tank.

Drainage system
The presence of a float-type switch in the drainage and sewer system allows the pump to be automatically turned off at the moment the tank is empty. The signal for stopping the operation will be given by the barorel controller located in the float device

The functionality allows the connection of two pumps to one float switch. In this case, the pumping units will work in turn. One will begin to fill the tank when the float is in the low position, and the second will come into operation when the switch is at the top.

However, experts point out the low efficiency of the system and pay attention to the potential differences with the supply of domestic water during the filling of the tank.

Equipment maintenance and repair

The float switch is a structurally simple and affordable device. It reliably and efficiently functions even in an aggressive environment and is not afraid of intense loads. Subject to the operating rules declared by the manufacturer, it develops the entire warranty period and after that also continues to fulfill its obligations in a quality manner.

Pumping fluid out of the tank
The presence of a float allows you to control the operation of the pump and program it for the future. For example, a drainage unit can be installed in a place of constant flooding. When the water level reaches the set level, the switch will lock it and immediately signal the pump to start pumping

If the module is used only in a complex of facilities dealing with water disposal or water supply, regular maintenance is not required. The aquatic environment is considered the least problematic and does not have any negative impact on the equipment.

Hazardous float switch
The float switch, which controls the operation of the drainage system, is subjected to heavy loads, as it is constantly located in a liquid medium containing a large amount of impurities, fragments of fine gravel, sand and organic residues

If the field of activity of the float is located in more aggressive, difficult conditions, for example, in sewer or fecal pits, the device requires more serious attention.

Plumbers recommend at least once a month to qualitatively rinse the float from the hose, in order to prevent the latter from sticking to the pressure pipe or pump walls during daily work. If the equipment is regularly rinsed with a jet of water, it will last much longer and will not lose working capacity even over time.

The most common breakdowns of the unit include burnout of contacts in the power cable, damage to the insulation layer, violation of the tightness of the housing and the penetration of moisture there. In the event of such problems, all defective elements must be replaced immediately, since they cannot be repaired.

Disassembled float switch
The internal arrangement of the float controller is not difficult. The device, as a rule, is reliable, works for a long time and does not cause owners any trouble

If the electronic module directly fails, the owners will have to discard it and install a new one in the tank as soon as possible. It is not worth buying the first float element that comes across, even if its price pleases with its attractiveness.

It is better to contact a specialized service center and purchase a branded certified part with documents that fully meets all the requirements for this type of equipment.

Conclusions and useful video on the topic

Installation rules for a mechanical float switch to protect the storage tank from overflow. Curious moments of work that must be taken into account.

How to install a float switch in the tank with the option to control the water level and connect it to the notification circuit. All the intricacies of installing and connecting equipment with your own hands at home.

About the features and nuances of the functioning of float switches and their scope tells the head of one of the largest service centers.

In order for the pumping equipment to serve for a long time, efficiently and fully, it is necessary to equip it with one or more float switches. These small structurally simple units will take on the basic parameters of controlling the communication system and protect the equipment from unnecessary loads and dry running.

Installation of floats is not too complicated and even an inexperienced home master, having on hand step-by-step installation instructions, will cope with the work without any special problems. If there is no 100% self-confidence, it is quite appropriate to turn to plumbers. They will complete the communication complex with the necessary number of control parts.

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Visitors Comments
  1. Stepan

    Simple and reliable thing. I have never encountered a failure of a float switch. Although it is clear that the mikrik inside can fail, but you can see high-quality products.

  2. Novel

    I need a float switch that turns on and off with a depth difference of 30 cm. Do they happen with such accuracy?

    • Expert
      Amir Gumarov

      Good afternoon, Roman, now everything can be purchased.

      For example, the PDU-P501 float sensor, judging by the scheme in the passport, allows regulation even less than 30 centimeters (I attached the screenshot of part of the passport). If plastic products do not suit you, you can see the two-level sensor-switch PDS-03 (screenshot - attached).

      Attached photos: