How to protect the pump from dry running. Circulation pumps with flow sensor Versions with a vertical arrangement of plates

In order to prolong the service life of liquid flow devices, timely inspection, renewal and overhaul. But sometimes this is not enough for the pumps to work smoothly. A water flow sensor will come in handy. The protection relay prevents damage to the engine of surface, deep pumping equipment. Consider the types of equipment, conditions correct selection and do-it-yourself installation and adjustment technology.

In domestic water supply systems, there is a problem of lack of water, which leads to a “dry run”. The incoming liquid cools the elements of the system, serves as a lubricant and ensures normal operation. If there is no water, the system runs dry, causing deformation and breakage of parts, equipment failure. The problem occurs in pump models of any configuration.

Causes of dry run:

• wrong choice of performance of pumping equipment;
• violation of installation technology;
• deformation, pipe rupture;
• reduced water flow pressure;
• lack of control over the liquid level;
• debris in the suction pipe.

An automatic or mechanical water flow sensor for the pump is needed to eliminate the threat of dry running. The device in a given mode measures, monitors and maintains a constant level of water flow. If a failure occurs in the station system, the sensor is triggered, the pump is turned off in standalone, and when the flow level resumes, turns on.

Types of water flow switch

The most common configuration of a water flow switch for a pump is the petal type. The classical scheme of the device consists of the following elements:

• inlet pass pipe;
• a valve (petal) located on the wall of the inner chamber;
• isolated switch;
• springs of a certain diameter.

The reed switch closes and opens the power circuits that actuate the compression spring. The principle of operation of the sensor in the water flow: when the chamber is filled with liquid, the flow displaces the valve from the axis by force, acting on the magnet, which actuates the switch. The contacts close, the pump turns on.

There are several types of sensors with their own features of operation and the possibility of application.

Mechanical vane

The device is a device equipped with a blade, which is built into the pipeline. The principle of operation is standard: when the flow enters, the blade deviates, acts on the magnet. The contacts close, the switch sensor is triggered. The simplicity of the unit explains the wide range of applications. In addition, such sensors are practically not subject to wear and tear and do not require maintenance - there is nothing to break in them.

Mechanical piston

The device works on the basis of a magnetic piston system. The principle of operation: when the flow enters, the piston with the magnet rises, closing the contacts - the relay is triggered to start. Without flow, the piston drops to its original position, preventing dry running. The main advantage of the device is a variety of designs that allow you to mount the device in any position. Mechanical piston switches are used in high pressure systems.

Thermal

The device is equipped with a level meter for thermal energy dissipation from the built-in heating element. Depending on the change in the rate of heating of the liquid, the flow itself and the speed of its flow are recorded. The thermal sensor is used only for safe types of liquid. Due to the hot-wire principle, it is forbidden to use the relay to measure flammable substances, as well as liquids that change composition when heated.

Advice! When choosing a device, it should be remembered that not all units operate with constant changes in flow. Thermal sensors require cleaning of sensitive elements.

Ultrasonic

The universal pulse water flow sensor works on the principle of the acoustic effect. The instrument transmits an ultrasonic pulse through the flow, detecting the level of the liquid. The most common are products whose functionality uses the movement of vibrations of a moving fluid. The devices are suitable for any substances, including combustible ones, they are easy to install and maintain.

How to choose a water flow switch

Before buying a unit, you must carefully read the technical characteristics, scope, and capabilities of the device.

What to look for:

• breadth of the operating temperature range;
• amplitude of pressure level indicators;
• diameter of thread and mounting holes;
• protection class;
• application features;
• manufacturing material.

The easiest way to handle a metal water flow switch, the price of units starts from $ 25-30, but it all depends on the type of device. The body and working elements made of metal are characterized by high strength, which means that the apparatus will withstand long-term pressure loads from the fluid flow.

Important! The pressure indicator is selected according to the power of the pumping system - the characteristic affects the parameters of the fluid flow passing through the pipeline system.

Devices with two springs are considered especially practical, one of which controls the operation of the station according to the upper, the second - according to the lower pressure level. Are taken into account climatic conditions operation and recommended humidity level. The limit of maximum permissible loads is indicated in the characteristics of the protection class.

The size of the diameter of the thread sections and mounting holes is checked for subsequent mounting of the device. With perfect compliance with the elements of the pipeline, docking will not cause difficulties, there will be no leaks during operation of the equipment.

Overview of well-known manufacturers and prices

The most famous and reliable are several models in the price range of $ 30-40:

1. Genyo Lowara Genyo 8A. Manufacturer - Poland. The main direction of the company is the production of electronic equipment for control systems. The relay is designed to work in domestic water supply systems and is characterized by high quality, long term operation. By monitoring the flow pressure in the pipes, the sensor starts pumping system with a water flow rate of 1.6 l / minute. The unit requires connection to electricity, consumes 2.4 kWh. Worker temperature regime+5..+60 С.
2. Grundfos UPA 120. The manufacturer's factories are located in Romania, China. The device has small dimensions, is conveniently mounted and is indicated for individual water supply systems. That is, it can be used both in private buildings and apartments. The device starts up at a fluid flow rate of 1.5 l / minute, completely preventing the functionality of the system at idle. extreme indicator operating temperature+60 C.

The models have been tested and adapted to domestic working conditions. Numerous reviews characterize metering sensors as durable and practical units at an affordable price.

Mounting the relay on a pump or station

If installation of the device is required, the work can be done independently, especially if you have to leave and there is no way to constantly monitor the operation of pumping equipment.

When not to install a relay:

• if water is pumped from a well with a large volume, that is, fluid reserves are not limited, and the pump power is minimal;
• it is possible to turn off the unit when the water level drops.

Equipment installation rules:

1. It is important to monitor the membrane - the part must take a vertical position.
2. Installation is carried out to the section of the drain pipeline with threaded couplings. There is a special socket for this.
3. Before starting work, the thread is sealed with linen or other plumbing thread. Winding the thread to the end clockwise will increase the reliability of fastening and fixation.
4. Factory sensors are equipped with an arrow drawn on the body - this is the direction of flow, which must match when installed.
5. When arranging a relay in pipelines for supplying water with dirt particles, cleaning filters are first installed. It is better to mount them next to the sensor in order to extend the life of the device.

Testing of the installed device is carried out with the connection to the power supply:

• the free ends of the contacts are connected to the core wire;
• grounding is mounted to the screw;
• the device is connected by connecting the device with a wire (watch the color of the corresponding wires);
• system performance is checked.

Worth knowing! If the device is connected correctly, then the pressure mark will begin to grow on the pressure gauge, and then the pump will turn off automatically as soon as the pressure gauge arrow goes beyond the boundary value.

Self-adjustment of the water movement sensor

The factory device is supplemented with bolts, tightening or loosening which can increase / decrease the compression of the spring. Bolts will be required if you need to set the sensor to a certain pressure level at which the mechanism is triggered.

Action algorithm:

• drain fluid from the system;
• wait for the pressure mark to take a zero value;
• start the operation of the pumping unit;
• run water back in the slowest mode;
• memorize the flow pressure indicator when the pump relay is turned off;
• drain the liquid again, fixing the indicators of the start of the system.

Now you need to open the relay, adjust the compression level of the larger spring with a bolt - this will trigger the device when the pump starts. Adjustment is made taking into account the fact that strong compression will increase the degree of pressure, and weak compression will reduce it. Then the compression force of the smaller spring is adjusted - here the limit of the maximum pressure level is set, upon reaching which the relay will automatically turn off the pump.

As soon as the adjustment is completed, start the system, evaluate the result of the work when filling the pipeline and draining the flow. If adjustments are needed, repeat the procedure. Checking the functionality and adjusting the operating parameters is an annual procedure that extends the life of the device.

flow sensor- a device that generates an output signal in the presence of a liquid or gas flow. They are installed in pipelines and air ducts, where the presence of the flow of the working fluid is a critical parameter.

This sensor is also called flow switch, because its principle of operation is similar to the one with the only difference that its operation is caused not by the appearance of a control voltage on the coil, but by the presence of a liquid or gas flow. But the result of the operation of the flow sensor, as well as a conventional relay, is a change in the state of the output contacts to the opposite ones.

As a rule, the sensor has a normally closed (NC) and normally open (NO) contact. When a flow of the working medium appears, the NC contact opens, and the NO contact closes.

There are several types of flow sensors:

Petal flow switch

The figure shows a diagram of the petal-type duct sensor.

As the name implies, the main working element of this type of flow sensor is a flexible petal that contacts the working medium and deviates from the vertical position in case of flow. The petal is mechanically connected to the output contacts and changes their state when it bends itself.

Leaf switches Caleffi (left) and Danfoss (right)

Turbine flow sensor

The figure shows a diagram of a turbine-type flow sensor.

Such sensors are a small turbine, the rotor of which is equipped with a magnet. When the flow of the working substance passes through the device, the turbine begins to rotate, resulting in a magnetic field that is converted into electrical impulses that enter the electronic circuit of the sensor. The electronics cause the output contacts to change state when flow is present, just as in a lobe sensor.

Thus, such flow sensors have two types of outputs: output contacts (NO and NC) and pulse output. The latter is used to determine the flow rate: the higher the pulse repetition rate, the greater the flow rate.

Flow sensor (turbine) for Ariston boiler

An example of this type of sensor is a flow switch. gas boiler Ariston. When a flow occurs (when the user opens a faucet hot water), the sensor generates an output signal and switches the boiler to the DHW heating mode.

Using flow sensors

Flow sensors most often perform protective, informational or control functions.

The protective function is associated with the detection of the presence of flow in systems where its absence can lead to emergencies or equipment breakdowns. So, for example, they protect pumps, because when working in the absence of water flow, they overheat and fail. You can also determine the lack of air flow in ventilation systems when the filter is clogged, the damper is closed, or the fan breaks down. With the help of a flow switch, you can detect leaks in water supply systems, determine the absence of water in storage tank etc.

The information function of the flow switch is spoken of when the presence or absence of a flow is not associated with an emergency, but is a significant event in the system that the user needs to know about. In such cases, the sensor operation is used to turn on a light or sound indication, or to generate a message on the operator panel.

The flow switch performs the control function when other equipment is turned on or off at its signal. For example, in DHW systems when the user opens the faucet with hot water, the gas boiler must turn on the pump and switch to DHW heating mode. This happens just when the flow sensor is triggered after the tap is opened.

Flow switch connection diagram

The following figure shows typical scheme turn on the flow sensor for the pump.

In the absence of flow, the NO contact 1-2 is open, and the NC contact 1-3 is closed, the power circuit is open, the pump is stopped. When water flows through the relay, its contacts change their state, the pump power circuit closes and it turns on.

Careful attitude to the equipment that provides water supply, significantly extends its working life, guarantees uninterrupted operation of the system. This requires not only timely inspection and proper care, but also equipping the pumps with a full range of protection devices. It is much cheaper to prevent the possibility of a serious breakdown than to repair or buy a new unit. Do you agree?

Installing a water flow switch will protect the engine of both surface and deep pumping equipment. Indeed, most often when a motor burns out, it is easier to buy a new pump than to change it. We will tell you how this important protective device works, how to choose it and include it in an autonomous water supply.

The article contains valuable advice for the installation of pump protection devices against operation in "dry running" conditions. The technology of customization for individual requirements has been disassembled. For better perception A considerable amount of information is accompanied by photographs, diagrams, video reviews and manuals.

In domestic water pipes, an accident-threatening action quite often occurs. pumping station without water. A similar problem is called "dry running".

As a rule, the liquid cools and lubricates the elements of the system, thereby ensuring its normal performance. Even a short dry run leads to deformation of individual parts, overheating and failure of the equipment engine. Negative consequences apply to both surface and deep pump models.

Dry running occurs for various reasons:

• wrong choice of pump performance;
• unsuccessful installation;
• violation of the integrity of the water pipe;
• low fluid pressure and lack of control over its level, for which they are used;
• accumulated debris in the pumping pipe.

An automatic sensor is necessary in order to completely protect the device from the threats posed by lack of water. It measures, controls and maintains the constancy of the parameters of the water flow.

Pumping equipment equipped with a sensor has many advantages. It lasts longer, fails less often, consumes electricity more economically. There are also relay models for boilers

The main purpose of the relay is to independently turn off the pumping station in case of insufficient fluid flow power and turn it on after normalization of the indicators.

Design and principle of operation

The sensor has a unique device, thanks to which it performs its immediate functions. The most common modification is the petal relay.

The following important elements are included in the classical structure scheme:

• an inlet pipe that passes water through the device;
• a valve (petal) located on the wall of the inner chamber;
• isolated reed switch that closes and opens the power supply circuit;
• springs of a certain diameter with different compression ratios.

At the time when the chamber is filled with liquid, the force of the flow begins to act on the valve, displacing it around the axis.

The magnet built into the reverse side of the petal comes close to the reed switch. As a result, the contacts are closed, including the pump.

The flow of water is understood as the speed of its physical movement, sufficient to turn on the relay. Reducing the speed to zero, resulting in a complete stop, returns the switch to its original position. When setting the response threshold, this parameter is set taking into account the conditions of use of the device

When the flow of fluid stops and the pressure in the system drops below normal, the spring compression weakens, returning the valve to its original position. Moving away, the magnetic element ceases to operate, the contacts open and the pumping station stops.

Some modifications are equipped with a return magnet instead of springs. Judging by the feedback from users, they are less affected by small pressure surges in the system.

Petal relays are characteristic a large number of pluses. Among them are a simple and unpretentious design, instant response, no delays between repeated responses, the use of an accurate trigger to start equipment.

Depending on the constructive solution there are several other types of relays. These include rotary devices equipped with a paddle wheel rotating in a water stream. The speed of rotation of the blade in them is controlled by touch sensors. In the presence of liquid in the pipe, the mechanism deviates, closing the contacts.

There is also a thermal relay that operates in accordance with thermodynamic principles. The device compares the temperature set on the sensors with the temperature of the working medium in the system.

In the presence of flow, a thermal change is recorded, after which the electrical contacts are connected to the pump. In the absence of water movement, the microswitch disconnects the contacts. Models are characterized by high sensitivity, but they are quite expensive.

Instrument selection criteria

When choosing equipment that controls the strength of the water flow, you should carefully study it. specifications.

Particular attention should be paid to the range of operating temperature and pressure for which it is designed, the diameter of the thread and mounting holes, the protection class, and the nuances of use. It is also important to clarify what materials the product is made of.

Experts consider devices made of brass to be the most reliable and durable, of stainless steel, aluminum. These materials protect the structure from the critical consequences of a frequent phenomenon in plumbing systems - hydraulic shocks.

Considering different modifications of the relay, it makes sense to purchase an option made of metal. The body and working components of such devices are characterized by increased strength.

This fact allows the equipment long time Withstand heavy loads arising due to the significant fluid passing through the sensor.

The pressure value at which the relay operates must correspond to the power installed pump. The parameters of the water flow circulating through the pipeline depend on this characteristic.

It is advisable to choose a device with two springs that controls the operation of the pumping station according to certain lower and upper pressure marks.

The operating temperature range of the sensor directly indicates the possible area of ​​its application. For example, for hot water circuits and heating systems, models with a high boundary temperature are intended. For pipelines with cold water quite enough range up to 60 degrees

Another important criterion worth mentioning is the climatic conditions necessary for the operation of the product. This is the recommended air temperature and humidity level that the device needs to provide so that it can work with the best performance.

Maximum permissible loads for a particular device determines the protection class specified in the technical specifications.

When buying a flow sensor, you should check the diameter of the thread section and the dimensions of the mounting holes in the equipment: they must fit perfectly with the elements of the pipeline. The correctness and accuracy of further installation, as well as the efficiency of the relay after installation, depend on this.

Trustworthy Instruments

Among the entire range of relays, two models are most in demand, located in approximately the same price category - about $ 30. Let's consider their characteristics in more detail.

Genyo Lowara Genyo 8A

Development of a Polish company engaged in the production of electronic equipment for control systems. It is intended for application in household water supply systems.

Genyo allows for automatic pump control: starting and shutting down based on actual water consumption, preventing any pressure fluctuations during operation. Also, the electric pump is protected from running dry.

The main purpose is to control the pump and control the pressure in the pipes during operation. This sensor starts the pump when the water flow exceeds 1.6 liters per minute. It consumes 2.4 kW of electricity. The operating temperature range is from 5 to 60 degrees.

Grundfos UPA 120

Manufactured in factories in Romania and China. Maintains the stability of the water supply in rooms equipped with individual water supply systems. Prevents pumping units from idling.

Relay trademark Grundfos is equipped with a high protection class, allowing it to endure almost any load. Electricity consumption in it is about 2.2 kW

The automation of the device starts at a flow rate of 1.5 liters per minute. The boundary parameter of the covered temperature range is 60 degrees. The unit is produced in compact linear dimensions, which greatly facilitate the installation process.

Liquid flow switches are installed for devices that need constant control and compliance with a certain operating mode. Often they complete the equipment at the production stage. However, there are circumstances where a separate mounting of the sensor is required.

Rules for installing relays in the system

Installation safety device, which determines the presence or absence of water flow in the system, is a reasonable step in cases where it is not possible to be constantly present during the operation of pumping equipment.

It is not required only in two cases:

1. Water is pumped from a large well with unlimited resources by a low power pump.
2. It is possible to independently turn off the unit when the water level drops below the designated norm.

The device is installed on horizontal sections of the pipeline. In this case, it is necessary to ensure that the membrane takes a stable vertical position.

The device is mounted to the drain pipeline using a threaded coupling. Usually a special socket is provided for this.

If there is no hole for mounting the sensor in the pumping equipment, you can replace it with a brass tee. In addition to the relay, a pressure gauge is connected to it, showing the current pressure in the network.

Before proceeding with the direct screwing of the device, it is advisable to seal the thread well with flax or thread sold in specialized departments.

It is better to wind it in a clockwise direction towards the end. This method of fastening increases the reliability of fixation.

In order not to damage the relay, you should screw it very carefully, slightly tightening it with a wrench. The optimal distance between the product and the pipeline is at least 55 mm

When installing the factory sensor, it is necessary to focus on the arrow shown on the case. The direction indicated on it must coincide with the direction of flow of the liquid passing through the device.

If contaminated water is transported through the pipeline, it is recommended to install cleaning filters, placing them near the sensor. Such a move will ensure the correct operation of the product.

At the final stage installation work the dry-running relay is connected to the electrical network:

• a wire core is screwed to the free ends of two groups of contacts;
• a ground is attached to the sensor screw;
• the device is connected to the pump by connecting two devices with an ordinary wire in compliance with.

After connecting to the network, the only thing left is to check the system's performance. The fact that the device is ready for full operation will be indicated by the growth of pressure marks on the pressure gauge and automatic shutdown pump at the moment of overcoming the limit value.

Self-adjustment procedure

There are special bolts in the sensor for adjustment. By loosening or tightening them, you can reduce or increase the compression force of the spring.

Thus, the pressure level is set at which the device will operate.

Almost always, manufacturing companies produce equipment with adjusted settings. Despite this, sometimes additional self-adjustment is required.

In most cases, the setting automatic equipment causes no difficulty.

It is advisable to adhere to the following algorithm:

• drain the fluid from the system until the pressure mark reaches zero;
• turn on pumping unit and slowly run the water back;
• fix the flow pressure indicator when the pump is turned off by the sensor;
• start draining again and remember the indicators at which the pumping equipment will start working;
• open the relay and adjust with the adjusting bolt the minimum level of compression of the larger spring required to operate the device and start the pump (more compression increases the degree of pressure, less - reduces);
• in a similar way, adjust the compression force of the smaller spring mechanism by setting the boundaries maximum pressure, upon reaching which the relay measuring the water flow will turn off the pump.

After completing all the described manipulations, you should make sure that the adjustments made are correct. To do this, the pipeline is filled with liquid, and then it is drained, evaluating the reaction of the sensor while reaching the set values.

If the test result is not satisfactory, the procedure is repeated.

Having insufficient experience and qualifications, it is better to seek help in adjusting from specialists. They will analyze the specific situation, take into account the technical characteristics of the equipment and select the most correct values ​​​​of the pressure level.

In order for the pipeline through which the liquid passes to work properly and stably, a regular annual check of the flow sensors is carried out. If necessary, the setting of the operating parameters is adjusted.

Conclusions and useful video on the topic

Structure, components and principles of operation:

The process of connecting the device in stages:

Read more about how to adjust the trigger level in the relay:

A relay that controls the flow of water in the pipeline will significantly increase the usability of pumps and extend their life for a long time. Neglect installation safety device highly undesirable, since it not only automates the operation of the equipment, but also protects it to the maximum from possible problems that occur due to idling.

Do you want to install the flow switch yourself, but are a little confused by the instructions? Please ask your questions, and we and the visitors of our site will try to help you.

Or maybe you have successfully coped with the installation and configuration of the device and want to give useful advice other newbies? Write your comments in the block below, add a photo of the installation or setup process - your experience will be useful to many home craftsmen.

The water flow sensor for the pump is an integral part of the equipment designed to protect the device from running dry. The sensor is small and simple design, which allows you to install it even for a beginner.

Features and Benefits of the Water Flow Sensor

Often there are situations in which the pump starts at the moment of complete absence of liquid in the pipeline. This provokes heating of the motor of the unit and its further breakdown. To avoid such situations, a fluid flow sensor should be used. This device works automatically and controls the flow of water inside the pipeline. If the amount of liquid passing through the sensor is less than the norm, the device automatically turns off the pump. Thus, the water flow switch not only prevents the pump from running dry, but also maintains normal operating conditions for the unit.

The benefits of using a sensor include:

• Reducing the electricity consumed by the pump and saving money;
• Protection of equipment from breakdowns;
• Extending the life of the pump.

Among other things, the water flow switch for the pump is distinguished by its modest dimensions, low cost and ease of installation.

Water flow switch - principle of operation and design

The main function of the sensor is to turn off the pumping equipment in the event of a drop in water level or an increase in pressure in the pipeline. If the amount of water increases or the pressure drops, the liquid flow indicator restarts the equipment. Its structural elements are responsible for the stable performance of the tasks assigned to the relay.

The device device consists of the following parts:

• A pipe through which liquid enters the device;
• A membrane that plays the role of one of the walls of the inner chamber of the device;
• Reed switch, which is responsible for opening and closing the circuit in wiring diagram pump;
• Two springs of different diameters - by compressing them, the water pressure is controlled, at which the fluid flow sensor will be triggered.

The principle of operation of the relay is as follows:

1. When it enters the internal chamber of the device, water exerts pressure on the membrane, thereby shifting it to the side;
2. The magnet located on the back of the membrane gets closer to the reed switch, due to which its contacts close and the pump turns on;
3. If the water level drops, then the membrane with the magnet moves away from the switch, which leads to the opening of its contacts and turning off the pump.

Installing a liquid flow detector in a pipeline is quite simple. To do this, you need to study the features of connecting the device and its correct configuration.

Device connection diagram

The performance of a relay is highly dependent on its correct installation. It must be remembered that the device can only be installed on those sections of the pipeline that are located horizontally. In this case, it will be necessary to ensure that the sensor membrane is in a vertical position. Correct scheme The relay connection looks like this:

During installation, the sensor must be connected to the drain part of the pipe by means of a threaded connection. The distance at which the relay must be located from the pipe must be more than 5.5 cm.

On the body of the device there is an arrow indicating the direction of circulation of the liquid. When installing the device, make sure that this arrow coincides with the direction of the water flow in the system. If used for domestic purposes dirty water, then a cleaning filter should be installed in front of the sensor.

The main task of any water supply system is not only to provide water to the consumer, but also to implement its uninterrupted operation in automatic mode without breakdowns. For this purpose, the commonly used pressure switches and dry running, float devices for monitoring the liquid level are intended. These devices, in addition to automating the operation of the system, protect the pump from dry running and, as a result, from overheating and failure. The water flow switch for the pump is less known and common, but is also designed to automate the operation of the plumbing system and protect its main equipment from failure.

The flow switch is designed to monitor the flow of liquid in systems of cold and hot water supply, heating, cleaning and cooling installations.

Its main purpose is to protect electric pumps, motors and other devices from operation in the absence or small amount of water in the system, leading to overheating and equipment failure.

Fig.1 Appearance of the flow switch

The relays are designed for installation in a pipeline and allows you to automate the process of controlling the supply of liquids in domestic and industrial systems.

The water flow sensor for the pump is used in the following cases.

• If there is no hydraulic accumulator in the system. This does not allow the installation of a pressure sensor designed to be paired with expansion tank, it is better to use a flow sensor to protect the electric pump.
• In low pressure systems. The minimum threshold for triggering typical models of pressure sensors is 1 bar, that is, at a lower pressure in the system, the pump will always be turned off. Flow devices have a wider range of action, which can be expanded with adjustments. This allows the use of equipment protection devices in underpressure systems.

To adjust to work with a wide range of pressures, some petal models are equipped with petals different area providing different resistance to water flow. Sometimes notches are applied to the blade indicating the length. When installed, it is cut to obtain the required set pressure according to the table with various combinations of the length of the petal and the internal diameter of the pipeline.

Figure 2. Flow switch with adjustable blade length

• The vast majority of flow relays are designed to operate in heating systems, so the temperature of their working fluid can be 100 C or more.

Device and principle of operation

The principle of operation of the flow switch is based on the mechanical action of the water flow in the pipeline on the sensor that controls the electronic circuit for turning on and off the electric pump. Relays have a different principle of operation and, depending on the design of the sensor, are divided into several types.

Petal relays

One of the most common types, the main elements are lobe sensor with a magnet located in the water flow and a reed switch placed in the device case and reliably isolated.

Fig.3 Petal mechanical relay

When the water flow passes through the pipeline, the vertically located petal sensor rotates along its axis and deviates from the vertical position, bringing the built-in magnet closer to the reed switch. Its contacts inside the cylinder close and through the triac (double symmetrical thyristor) the pump is connected to the power source.

In the absence of water in the pipeline, the petal returns to its original position, moving the magnet away from the reed switch and thereby opening its contacts.

This leads to the termination of the supply voltage to the pump through the hemistor, as a result of which it turns off.

Fig. 4 External view of the relay with a reed switch and a sevenistor

Rotary relays and flow type sensors

Rotary sensors are mainly used to measure and control fluid flow. Structurally, they are made in the form of a paddle wheel rotating in a fluid flow, its rotation speed is recorded by sensor sensors. Electronic circuit allows to carry out analog, frequency or discrete control of equipment operation.

Fig.5 Rotary sensors

Piston devices

The piston is placed in the valve seat and, under the influence of water pressure, moves in a vertical direction to a height proportional to the flow force. Permanent magnet, mounted on the piston, approaches the reed switch and the contacts close in it. Piston units can be installed in horizontal and vertical pipelines due to the built-in return spring that returns the piston to its original position in the absence of flow.

Rice. 6 Working principle and appearance piston relays

Water flow switches, unlike pressure and dry running switches, float switches, are not so widely used for automatic control water electric pumps in systems domestic water supply. This is due to the fact that they cannot work independently in the water intake system - to turn them on, it is necessary to create a flow of water and turn on the pump by other devices. Relays are designed to turn off electric pumps and are often built into electronic water supply control units in conjunction with other automation.