Dry running of the pump is the operation of the unit in the absence of the required amount of pumped liquid. If water or other liquid runs out, then the pump dry-running protection is activated. It can be presented in the form of several different devices, the most common of which is a dry-running relay for a pump.

Dry running sensor for pump - principle of operation and design

There are several of the most common devices, the main task of which is to protect pumps from dry running. These include:

• Dry running protection relay;
• Sensor for monitoring the volume of the pumped liquid;
• Water quantity sensor - float.

Each of the listed devices is used in different pumps with different tasks and functions. The most commonly used in pump manufacturing is the dry-running protection relay. It has a fairly simple design, but it shows high efficiency in the operation of centrifugal, vortex and other types of equipment.

The relay is a simple electromechanical device designed to control the pressure inside the pipeline. As soon as the pressure falls below the minimum permissible limits, the electrical circuit will instantly open and the unit will shut down.

The relay device includes a sensitive diaphragm that reacts to pressure fluctuations and a group of contacts, which in the normal state is in the open position. With a drop in pressure, the membrane begins to press on the contacts, which leads to their closure and the cessation of the supply of electricity to the pump motor.

Each dry-running pump sensor is designed for a specific pressure environment. Depending on the settings of the manufacturer, the equipment can operate in the range from 0.1 to 0.6 atmospheres. As a rule, the relay is mounted on a surface outside the pump casing, however there are devices mounted inside the device.

Installing a protective relay in a system with a hydraulic accumulator - is it worth the risk?

The protective relay will function normally with any pipeline that does not have a hydraulic accumulator in the design. On the other hand, you can put the relay in tandem with a hydraulic accumulator, but such an installation will not give full protection against dry running.

The reason for this lies in the principle of operation and the structural features of the sensor: the protective relay should be installed in front of the hydraulic accumulator and the fluid pressure switch. In this case, a dry-running valve is installed between the safety device and the pumping unit.

In this case, the membrane of the relay will be under the influence of constant pressure created by the accumulator. This is a fairly typical arrangement, but in most cases it will not help protect the pump. For example, consider such a case: when the pump is on, which pumps out liquid from an almost empty container, the remaining liquid remains in the accumulator. Since the lower pressure threshold is set by the manufacturer in the range of 0.1 atmospheres, then in fact there is pressure, but the pump will run idle.

As a result, the pump motor will stop working only when the accumulator becomes completely empty, or when the engine itself burns out. As a conclusion, we can say that it is better to equip systems with hydraulic accumulators with other protective devices.

How to connect a dry running sensor - the correct procedure

Anyone who has the slightest understanding of the operation of electrical devices can connect the relay. First of all, you need to remove the protective cover of the device. There are 4 contacts under it - two for the input and two for the output. The connection diagram to the input "L1" and "L2" and to the output "M" of the pump itself is shown in the image below:

It should be remembered that the cross-section of the wires supplying the pump must correspond to the capacity of the unit. The socket must be grounded.

Setting the connected protective relay

A dry-running relay for a pumping station or a domestic pump must not only be connected, but also correctly configured. This should be understood to mean the adjustment of the relationship and stiffness between the included contacts and the platform, which lends itself to the action of the operating pressure. These characteristics can be adjusted by changing the stiffness of the spring, which must be loosened or compressed by turning the nuts. Below, as an example, the location of these nuts in the RDM-5 relay is shown. Most other modern safety devices have a similar design and the adjusting nuts are located in the same way.

According to the factory settings, the minimum pressure for relay actuation is 1.4 atm. The maximum pressure, in this case, is equal to 2.8 atmospheres. If it is necessary to change the minimum pressure threshold, then for this nut "2" must be tightened clockwise. In this case, the upper pressure threshold will also increase. The difference between them will always be 1.4 atmospheres.

If it is required to adjust the difference between the lower and upper pressure thresholds, for this it is necessary to turn the nut "1". When rotating it clockwise, this value will increase, and counterclockwise, it will decrease.

LP 3 protective relays - description and characteristics

The device of this model of the hydrostop type is used in water supply systems, and is designed to turn off borehole and surface pumps in automatic mode. The devices are switched off openly immediately after the liquid level falls below the permissible limits. The main technical characteristics of the relay include:

• The maximum level of the switched current is 16 A;
• Pumped water temperature range - from 1 to 40 ° C;
• Operating pressure range - from 0.5 to 2.8 atmospheres;
• Electrical protection class IP44.

The manufacturer provides a 1 year warranty for this relay type model. The device shows the reliability and effective protection of the pumps during operation.

Pumping equipment serving pipeline systems through which a liquid medium is transported especially needs protection at the moment when the pressure of the liquid drops or it stops flowing altogether. To provide such protection in situations when the pumped liquid is not supplied to the pump, it is equipped with automatic sensors - dry running relay. Various types of such devices can be used for a pumping station.

Why pumping equipment must be protected from dry running

From whatever source the electric pump is pumping water, this equipment may find itself in a situation where the liquid stops flowing into it. It is these situations that lead to the pumping station starting to idle (or, as they say, dry running). The negative consequence of operating the pump in this mode is not even a useless waste of electricity, but intensive heating of the equipment, which ultimately leads to deformation of its structural elements and rapid failure. Water simultaneously acts as a lubricating and cooling liquid, so its presence inside the pump is a must.

For this reason, the presence of a relay that provides protection against dry running of a borehole pump (or circulation pump) is practically mandatory. Most modern models of pumping equipment have built-in relays. However, these pumps are very expensive. For this reason, users often purchase dry-running relays separately.

Basic means of protection

To protect the pump from dry or idle running, various types of devices are used, the main task of which is to stop the operation of the equipment at the moment when water stops flowing into it. These include, in particular:

• pump dry-running protection relay;
• water flow sensor;
• pressure switch with dry running protection option;
• sensors that monitor the level of liquid in the water supply, which can be float switches or level control relays.

The differences between all of the above devices lie both in their design and principle of operation, and in the areas of their application. In order to understand in what situations the use of one or another type of relay that protects pumping equipment from dry running is most expedient, you should get acquainted with each of them in more detail.

Pump dry-running relay characteristics

A dry-running sensor for a pump refers to an electromechanical type device that monitors whether there is pressure in the system through which water is transported. If the pressure level is below the standard threshold, such a relay automatically stops the operation of the pumping equipment, opening the circuit of its electrical supply.

The dry-running relay for the pump consists of:

• membrane, which is one of the walls of the inner chamber of the sensor;
• a contact group that provides closing and opening of the circuit through which electric current flows to the pump motor;
• springs (the degree of its compression regulates the pressure at which the relay will operate).

The main elements of the dry-running relay

The principle by which such a dry-running protection relay works is as follows.

• Under the pressure of the water flow in the system, if its level corresponds to the standard value, the membrane of the device bends, acts on the contacts and closes them. In this case, the electric current flows to the pump motor, and the latter operates normally.
• If the water pressure is insufficient or does not enter the system at all, the membrane returns to its original state, opening the electric power circuit of the pumping unit and, accordingly, turning it off.

Situations when the pressure of the liquid in the water supply systems drops sharply (which means that the pump needs protection against dry running) are caused by various reasons. Among such reasons are the depletion of the natural source of water, clogged filters, too high location of the self-priming part of the system, etc.

The pump dry-running protection relay is usually installed on the surface of the earth, in a dry place, although there are models made in a moisture-proof casing that can be mounted with pumping equipment in a well.

Relays that prevent dry running of the pump work more effectively when they are installed in systems not equipped with a hydraulic accumulator, which are served by a surface circulation pump. It is, of course, possible to install such a relay in a system with a hydraulic accumulator, but in this case it will not be able to provide one hundred percent protection of the pumping unit from dry running. At the same time, the relay connection diagram looks like this: they place it in front of the water pressure sensor and the hydraulic accumulator, and immediately after the pumping station a check valve is installed, which prevents the water from moving in the opposite direction. With this connection, the membrane of the dry-running switch is constantly under water pressure created by the accumulator. This can lead to the fact that the pump, which will not receive water from the source, simply does not turn off.

Effective protection of the pump against dry running in cases where it serves systems in which a hydraulic accumulator is installed is also possible, but other types of devices are used to solve this problem.

Water flow sensors

In situations where such an undesirable phenomenon as dry running occurs, the fluid flow that enters the pump either has insufficient pressure or is completely absent. In order to control the presence of a flow and its operating parameters, special devices are used, which are called water flow sensors. By design and operating principle, they can be electromechanical (sensors) or electronic (controllers).

Relay or water flow sensors

There are two types of electromechanical water flow sensors:

• petal;
• turbine.

The main working element of the sensors of the first type is a flexible plate installed in their inner cavity having a cylindrical cross-section. In the event that a fluid flow in the system is present and has sufficient pressure, such a plate equipped with a magnetic element is as close as possible to a reed switch, and its contacts are in a closed state. If the pressure of the fluid flow decreases or it disappears altogether, the flexible plate moves away from the switch, its contacts open, which leads to the shutdown of the pumping unit.

Turbine type flow sensors have a more complex design. It is based on a small turbine, in the rotor part of which an electromagnet is installed. The principle of operation of such a sensor, which is also capable of protecting the pump from idling, is as follows. The fluid flow rotates the turbine, in the rotor of which an electromagnetic field is created, which is then converted into electromagnetic pulses, read by a special sensor. The decision on whether to turn on or off the pumping equipment serving the system is made by the sensor depending on how many pulses the turbine sends to it per unit time.

Automatic pump control sensor "Turbi"

Electronic water flow controllers

An even more complex design is distinguished by electronic water flow controllers, which combine the functions of both a pressure switch and a device that protects pumping equipment from dry running. Such controllers, also called electronic pressure switches, although not cheap, replace several monitoring and control devices at once. Installed in water supply systems, electronic pressure switches not only protect the pumping system from dry running, but also allow you to control the pressure and parameters of the fluid flow. When such parameters of the system do not correspond to the standard values, the electronic sensor automatically turns off the pumping equipment.

If a pump with a small head reserve is used to service water supply systems, then they can only be equipped with an electronic relay. When a pump is used in the system with a large margin for the pressure it creates, a hydraulic accumulator and a separate pressure sensor are needed, since the electronic relay is not regulated by the maximum shutdown pressure of the pumping unit. The use of only an electronic relay in such cases can lead to the fact that when an excess pressure is created in the system, the pumping station simply does not turn off.

Sensors that monitor the water level in the system

Water level control sensors, which are installed mainly in a water supply source - a well, a well or a tank, are also capable of preventing the occurrence of situations when the pump of the water supply system is idling. Thus, by means of such devices, the borehole pump is protected from dry running (or a pumping unit that pumps water from a well). By design, level control sensors can be float and electronic.

Float sensors

There are two main types of float sensors. Some of them control the filling of containers with water, preventing cases of its overflow, and the second, which protect the pump from dry running, regulate the emptying of water containers, wells and wells. In addition, there are combined models that, depending on the connection diagram to the system, can perform both functions.

The principle of operation of a float water level control switch is quite simple. As long as there is liquid in the water supply, the float connected to the contact group is lifted up. The process of operation will not be interrupted until the water level in the source decreases to such an extent that the float drops and thereby opens the contacts through which electric current flows into the phase wire of the pump motor.

It should be noted that dry-running protection of the pump-pump using a float water level control sensor is the most affordable and most common method.

Electronic relays

Electronic water level control sensors are able to simultaneously solve two problems: to protect pumping equipment from dry (idle) running when the water level in the water supply decreases and to prevent cases of liquid overflow when filling tanks.

12.01.2019 Pyotr Andreevich 0

Dry-running relay for pump and station: installation and setting

Dry-running relay is a device designed to protect the water pump motor from starting in the absence of water. The pumping technology is designed so that water from the well acts as a coolant and lubricant, preventing overheating of the electric motor. Therefore, "dry running", when the pump operates without water, leads to serious damage, up to the complete failure of the equipment.

Dry-running sensor for pump: principle of operation

The reasons for the disappearance of water are different - the well has dried up, the suction hose has ruptured, the filters are clogged.

To prevent such troubles, a special protective sensor is introduced into the water main - a dry-running relay. In modern pumping stations, a similar device is included in the factory package. However, most of the budget pump modifications lack built-in protection.

Today there are several different modifications of protective devices. A standard dry-running protection sensor includes the following items:

• Diaphragm installed inside the relay housing.
• Opening contacts - automatically operate when the pressure in the water supply network drops below the set threshold.
• Adjusting spring. With its help, the sensor response limits are set.

When the water pressure is within the normal range, the inner membrane bends under its pressure, connecting the electrical contacts. As a result, the circuit is closed and the pump motor runs. When the water pressure suddenly drops below a certain level, the membrane straightens out, opening the contacts. The power supply to the motor is cut off and it stops.

It is possible to start the device again only by filling the system with water and creating the required pressure inside the sensor. A special spring is used to adjust the threshold for automatic shutdown of the pump. The setting range is approximately 1 atm.

Dry-running relay connection to the pumping station

The dry-running protection relay of the pump is often mounted at the top, in a place protected from dampness.

Waterproofing options are also commercially available, designed for downhole installation. These include float mechanisms that turn off the pump in case of a critical drop in the water level below a certain level. It is quite possible to mount the sensor with your own hands, without the involvement of expensive specialists.

All work consists of several stages:

• Installation of a protective relay is made only in conjunction with a water pressure sensor. The connection diagram of these devices must be strictly observed in accordance with the attached instructions of the manufacturer.
• The next step is to determine the location of the device. Most often, the relay is installed on the pipes leaving the pump and immediately after the pressure sensor.
• On the pipe section where the relay is planned to be installed, a tee fitting corresponding in diameter and thread is mounted.
• Next, you need to dismantle the idle speed sensor cover, and remove the plastic gasket under it. This will open access to the branch pipe, which should be connected to the tee fitting. Docking thread, in order to avoid leaks, should be sealed with linen winding, or special threads, such as "Tangit-unilok"
• A break is made in the power supply cable of the pump, where an idle protection relay is inserted. When the sensor contact is opened, the flow of electric current is interrupted and the pump stops working.

Dry running protection of the borehole pump

Float switches are commonly used to protect submersible pumps.

This device consists of a sealed case, which contains a freely moving steel ball and current breaker contacts. The float sensor is connected to a break in the supply circuit, in the same way as surface modifications. The float is lowered into the water together with a submersible pump, to which it is connected by a cable.

Since such a device is lighter than water, which can already be understood from the name "float", it always tends to float, but the cable does not allow it to do so. Therefore, the sensor is at such an inclination that the ball presses on the lever of the switch closure.

In this position, the equipment turns on and operates quietly. But when the water level drops below the location of the pump, the device hangs freely on the fastening cable, and the ball rolls to the other side of the case, releasing the spring-loaded lever. The contact opens and the supply of electricity to the motor is blocked.

In addition to float relays, conventional surface relays are also used for downhole pump modifications. Relatively recently, electronic devices have also appeared on the market that monitor changes in the water level inside the well and automatically turn off the power supply to the pump.

Dry-running relay adjustment

The pump with dry-running protection is automatically switched off, depending on the set value of the internal network pressure. To adjust this indicator, the sensor has a special adjusting screw connected to the spring.

When the screw is turned left and right, the spring is either relaxed or compressed. Thus, the required pressure is set at which the membrane will open the electrical contacts. On most models of protective relays, the lower limit is set at 1.4 atmospheres, and the upper limit is about 2.8.

These factory settings can be changed as desired. To increase the sensor response threshold, the spring screw must be turned counterclockwise, and to decrease the lower limit, it must be turned in the opposite direction.

When manually setting the threshold, you must ensure that it is not higher than the pressure that a normally operating pump creates. Otherwise, there is a danger that the equipment will not react at all to changes in the water pressure, which is fraught with damage to the electric motor during dry running.

Dry running is the operation of the pump without liquid. For most models, this mode is highly undesirable and can lead to failure. We figure out how to protect the pump from dry running.

The pump is a necessary part of the water supply system of a private house. But in order for the pump to work for a long time, it must be turned on and off periodically, preventing it from working without water. To protect the pump from dry running, several technical solutions have been invented. Let's get acquainted with their advantages and disadvantages and choose the best way to protect against dry running.

What is dry running

Most models are not designed to operate the pump in a dry condition. Such work is called dry (sometimes idle, which is not entirely correct).

Most manufacturers explicitly indicate in the operating manuals about the inadmissibility of dry running.

Let's figure out what are the reasons for this phenomenon and why it should not be allowed.

Wherever the water comes from, a situation periodically arises when the water runs out. For example:

• If the flow rate of the well is small, with a large analysis, it can simply be emptied. It will take some time for the well to fill up again.
• If the pump is located on the surface, the pipe through which the water is pumped out of the well may become clogged.
• If the water is supplied centrally, it may dry out in the line due to pipe breaks or technical work on the line, associated with a temporary interruption of the supply.

Why is dry running unacceptable in pump operation? The fact is that in most models, the water pumped out of the well plays the role of a cooling liquid. In the absence of water, the parts begin to rub against each other more intensively, as a result they heat up. Further, the process develops as follows:

• The heated parts expand, increase in size. Heat is conducted by the metal and to adjacent nodes.
• Details begin to deform.
• The mechanism is jammed due to changes in the shape and size of the parts.
• In the electrical part, due to a sharp voltage jump when the mechanical part is stopped, the motor windings burn out.

In order for the pump to break down irreversibly, five minutes of dry running is enough. Therefore, dry-running protection is a necessary component of any pumping station.

When contacting the service, the masters easily diagnose dry running as the cause of the breakdown - because of this, a number of characteristic distortions of parts arise in the mechanism.

Dry running is in most cases grounds for denial of service under warranty.

How to protect a pumping station from running dry

Today, several solutions have been developed that protect the pump from dry running by turning it off when the water supply is interrupted. Each of these solutions has its own strengths and weaknesses, so several protection systems combined together give the best effect.

But in order to determine how to create effective dry-running protection for your pump, you first need to find out which features are specific to the individual components.

Protection relay

This mechanism is quite simple in design. It responds to the water pressure in the system. As soon as the pressure drops below the permissible norm (this is a signal that water has stopped flowing into the pump), the device closes an electrical contact, and the pump power circuit is broken. When the pressure is restored, the circuit is closed again.

Depending on the model and the settings set by the manufacturer, the relay is capable of operating from a pressure drop from 0.6 (highest sensitivity) to 0.1 (lowest sensitivity) atmosphere. Usually this sensitivity is sufficient to detect the occurrence of an idle situation and turn off the pump.

The most common such mechanism is for surface-mounted pumps. But some models have a case that is protected from water ingress and can be mounted on deep pumps.

It is not recommended to install such a device if a hydraulic accumulator (GA) is provided in the system. The fact is that usually in this case, the installation of the protection device looks like this: "pump - check valve - safety relay - water pressure switch - GA". Such a scheme does not give 100% confidence that the pump will turn off during dry running, since the water contained in the accumulator can create a pressure of 1.4 - 1.6 atmospheres, which will be perceived as normal.

And then, if, for example, at night someone flushed the water in the tank and washed their hands, this will turn on the pump, but will not empty the GA. And if water does not flow from the well for some reason, then by morning the pump will already burn out due to dry running. Therefore, for systems with a hydraulic accumulator, it is better to look for other solutions to ensure protection.

Water flow control

To determine if there is a water flow through the system, two types of sensors are used:

• Lobe relays are the simplest in design. In them, the flow of water bends the plate, which, in the absence of pressure, will bend and short-circuit the relay contacts. Then the circuit that supplies the pump with electricity will be disconnected.
• The turbine relay is more perfect, but more complex in design. Its main element is a small impeller mounted on a shaft. The flow makes it lie, and the sensor reads the pulses generated by an electromagnet attached to the axis of the turbine. If the number of pulses falls below the reference value, the circuit is disconnected.

There are also combined water flow controllers. They can additionally include a pressure gauge, a check valve, a membrane relay to protect against a drop in water pressure and other components.

Such blocks are the most reliable, but due to the technical complexity, the cost of such a block can be quite significant.

Water level sensors

The water level sensor is placed in the shaft. It is most often installed in a set with a submersible pump, but there are models designed for use with ground pumping stations.

By design, there are two types:

In addition to the mechanisms described, there are many other systems for preventing dry running, for example, frequency converters. But these solutions do not apply to domestic plumbing because they are too expensive, bulky, or consume too much electricity.

Required tools and materials

To connect a pressure switch and a dry-running protection relay, you will need to prepare:

• The relays themselves.
• Tools for working with electrical wires: a knife for stripping contacts, screwdrivers.
• Wires to create an electrical circuit.
• Keys for mounting relays on highways.
• Means for sealing connections: sealants, rubber gaskets (usually included with the relay).

Having prepared everything you need, you can get to work.

Do-it-yourself installation of protection against dry running of the pump. Step-by-step instruction

You can see the wiring diagram of the pressure switch and dry-running fall protection in the figure:

The installation procedure is as follows:

After that, it remains only to test the system, to make sure that the relay does not interfere with the normal operation of the pump and properly disconnects it after going dry.

Despite the fact that the connection of any dry-running protection relay is not particularly difficult, there are some nuances, the understanding of which comes with the accumulation of practical experience. Therefore, it is especially important to listen to the recommendations of specialists in each case. Here's what the professionals advise on the selection, installation and adjustment of dry run protection mechanisms:

• Before buying, carefully study the passport of the selected relay and make sure that its sensitivity and other characteristics are at the proper level for your well and pump. You can study the passport directly in the store or find it on the manufacturer's page of the protective device and download it in pdf format.
• Make sure all wiring and circuitry to be created is adequate for the power being used. Otherwise, there is a risk that the conductor or relay will burn out.
• The most advanced protection system can be powerless if used ineptly. If any of the components has worked, do not restart the pump until you have found out the cause of the problem and made sure that it has been completely eliminated.
• Remember that every relay requires periodic verification and replacement. Replace expired protective system components promptly.

In addition, we offer several videos so that you can see the order of connecting the relay with your own paths:

Dry-running protection is a precaution that should not be neglected when connecting the pump.

Although the purchase and installation of the necessary devices requires some investment of time and money, but these costs are much lower than the losses that will have to be borne if the pump burns out.

Therefore, it is simply unreasonable to refuse to install protection in most cases.

The "dry" pump run is called its idle operation, when water for one reason or another has ceased to flow to it. The fact that in this case a waste of energy occurs is not the main problem: overheating and rapid wear of equipment are much more dangerous, because water plays the role of a lubricant and a cooler.

• Incorrectly selected equipment. It often happens that a too powerful pump model was chosen to equip the well. Another possible variant of the problem is that the apparatus was installed higher than the dynamic level of the well.

• The suction line is clogged.

• The pipeline has lost its tightness.

• Reduced water pressure. If a running pump is not protected against dry running, it can quickly fail due to overheating.

• The water is pumped from the tank. When the water in the tank runs out, the equipment goes to idle.

This is a control device that monitors the pressure level inside the water supply. If it falls too low, the pump stops immediately by opening the supply circuit.

The design of the protective device includes:

• Membrane. This role is played by the wall of the inner chamber of the relay.

• Contacts. They short-circuit or open the power supply to the pumping motor.

• Spring. The level of its compression indicates the limit of the fuse actuation (factory settings are in the range of 0.1-0.6 atm.).

Most often, the relay connection point is the ground surface (the place must be dry). However, on sale there are also devices in a sealed case, which are installed together with a pump in a well.

The dry-running protection relay operates on the following principles:

1. At normal pressure in the system, the membrane bends, and it closes the contacts. This allows electricity to flow freely through the circuit, allowing the pump to operate normally.

1. In the event of a weakening of the pressure of water, or a complete cessation of its supply, the membrane straightens, thus opening the electrical circuit. As a result, the pumping unit stops instantly: resumption of work is possible only in manual mode, before filling the device with water.

Pressure transmitters are characterized by a wider range of operation. They are able to respond to a decrease in pressure from 1 bar. Typically, this is how household pumping installations of central pipelines are completed (more specifically, fire extinguishing and water supply systems).

Water pressure gauge: pressure gauge and pressure switch

To protect against idle operation of the pump, several other devices have also been developed:

• "Float". A good option for protection against idling when water is pumped from another container or well. Here, not the pressure is monitored, but the water level inside the circuit. One of the types of floats reacts only to the filling level: the contacts open and the pump stops only after reaching the assigned filling limit. Frankly, such a device protects against overflow rather than dry running. A more suitable option are floats to fix the emptying level. In this case, the contact is opened after lowering the water in the tank or well below a certain level, which is oriented at the place of installation of the float. The disadvantage of this solution is that the well or pipeline does not always fit such a sensor.

• Level relay. A more modern modification of devices that respond to changes in water level are electronic sensors. They equip the wellbore or well at several points: when the water falls below the control device located immediately above the pump installation point, a command is sent to stop it. After the water level is restored, the equipment starts automatically. Such dry running control devices are highly reliable: they are often used when pumping water out of a container. In this case, the installation of the level switch itself is carried out indoors.

• Flow sensor. The main function of this device is to measure the flow of water through the pump. The device includes a valve and a switch. The valve is equipped with a spring and a magnet on one side. The water pressure sets the valve petals in motion, which provokes the contraction of the spiral and the activation of the magnet. The connected contacts provide the flow of electricity and the pump starts. When the water flow dries up, the spiral expands and the magnet moves to its original position. As a result, the relay contacts are disconnected and the engine stops.

In this case, there is usually some delay in response after the flow is stopped, but the performance of the pump is not particularly affected by this. Typically, flow sensors are used to protect low power boost equipment against dry running. Their main advantage is their compact size and low weight. The range of the fixed pressure here is from 1.5 to 2.5 bar.

• They are equipped with single-phase devices to provide protection against no-load and control: this is influenced by the parameters of the current and power of the device. The popularity of mini AKNs is due to their efficiency, ease of installation, low power consumption and reliability.

How to choose a dry-running protection relay

The selection of the optimal type of protection against dry running depends on the characteristics of the equipment and the characteristics of the well or well. On sale are systems developed for a specific place of installation of the pump - a well, a centralized pipeline, wells with different depths. Also, a lot depends on the performance of the source and the power of the pump. A noticeable influence on the choice of protection has the specifics of the operating conditions - the diameter of the shaft, the place of installation and the technical parameters of the pump used.

To control the operation of the pump, various models of dry-running relays can be guided by different parameters - the force of water movement into the pipes, its level or pressure. If a suitable head is present, the device turns on. After its disappearance or lowering below the boundary line, the station is disconnected. It is important to understand that if the binding is carried out to pressure, then false alarm situations may occur : this is when water, after pumping, is immediately consumed by the consumer, due to which the pressure will not be able to gain the required indicators. In this case, the relay will turn off the equipment, although there are no problems with the water intake. Therefore, when buying a sensor, it is important to take into account the maximum pressure developed by the pump.

Choosing a suitable protection option will make it easier to know the disadvantages of some of the above models:

• By pressure... There are situations when the pressure in the circuit is created not by water, but by compressed air. Under these conditions, the pump continues to run dry until the pressure reaches the set threshold.

• Contact with water. These models are designed to determine if there is water in the system. However, if the valve on the pump line is closed, it will run dry despite being full of water. Therefore, it is better if there are taps on the pump line at all: if they are necessary for maintenance of the pump, it is recommended to use a flow switch.

• By current consumption. Here, the response principle is based on the greater energy consumption of the pump when it is idling. However, these types of devices have a high cost, and sometimes even professional plumbers cannot figure out their settings.

• Flow switch. It is ineffective in creating pressure in the system by the pump itself.

In order for the dry-running relay to work normally, it is recommended to include a hydraulic accumulator in the water supply network (the volume is not important). If the pump is installed in a deep well with a good flow rate with a constant water level, or if it is operated by an experienced user, then the dry-running relay can be omitted.

The installation process of a dry-running relay consists of the following steps:

1. The sensor can only be installed on a network with a pressure switch, thanks to which the electric pump can operate in automatic mode. The pressure switch is installed in strict accordance with the accompanying instructions.

1. Next, you need to decide where exactly to install the dry-running relay. Usually it is mounted on the pressure pipe, near the pump outlet, right after the pressure switch.

1. The section of the water supply system, where the installation will take place, is freed from water. Before connecting, remove the cover from the device and unscrew the plastic insert. Further, with the help of the opened branch pipe, it is connected to the desired fitting. Thread sealing is carried out with sanitary tapes made of fluoroplastic or linen, impregnated with special pastes.

1. The device is switched sequentially at the point where the power circuit is broken (it can be connected anywhere in relation to the pressure sensor (before or after). There are special terminals to enter the mains wire and control wire. Before starting installation work, the mains cable must be pulled out of the socket.

You can also watch a video on how to connect a dry-running protection relay to a pump:

The device is designed in such a way that its adjustment provides for changes in the level of connection between the surface that responds to the working pressure and the contact group that should be triggered. For this purpose, the relay has screws that either compress or relax the springs. On almost all models, the factory settings set the lower response limit of 1.4 atm., The upper one - 2.8 atm. The user has the ability to choose their own indicators. To increase the lower limit of operation, the adjusting screw is turned from right to left, to lower it - vice versa.

It is important to understand that with an increase in the lower limit, a natural increase in the upper one occurs (the difference of 1.4 atm. Remains). A prerequisite for tuning is to set the cut-off limit of the relay lower than the pump pressure. If this moment is not taken into account, the pump will not react at all to dry running, which will cause its rapid failure.

Another adjusting nut allows you to change the difference between the extreme limits of the response of the device. As already mentioned, the factory setting is usually 1.4 atm. By tightening the nut, the difference can be increased up to 2 atm. In this case, there is also a change in the upper limit of the shutdown, which also follows the fate of the setting. It is very important that the level of the highest cut-off pressure does not exceed the value that the pump itself can produce. The decrease in the lower level and the difference in the boundaries occurs in the exact opposite - by unscrewing the adjusting nuts.

You can also watch a video on how to configure the dry-running protection relay:

Caveats:

• If the minimum setting is too low, it may happen that an error of 0.3 bar does not allow the relay to disconnect the voltage in time.

• If the limit is too high, the same error can trigger the dry-running protection and the pump will shut down for no reason.

• With a minimum dry running pressure, it will take more time to start the pump (you will have to drain the water from the accumulator).

• An error of 0.2-0.3 bar can provoke the so-called. "Rollback" of pressure. As a result, with a large volume of consumption, a sharp drop in pressure of up to 0.4 bar can be observed. To avoid idle shutdowns, you need to lower the idle pressure level.