Pump dry-running protection: why is it needed and how does it work? Dry running protection relay for well pump Pressure relay with dry running protection.

Reading time: 6 minutes.

Most private houses have an autonomous water supply, which is provided by a pump. With various layouts of systems that supply water, there is always a need for constant monitoring and control of the operation.

Automatic switching on and off occurs using a relay, which is triggered by changes in water pressure. If the water source dries up (does not have time to recover due to intensive intake), the pump’s protection against idle move and the pump turns off.

What is dry (idle) running?

Every natural spring water has its own specific resource, which depends on such parameters as depth, soil composition, intensity of movement groundwater. With intensive use, the water supply is quickly depleted, and if connected to centralized systems, accidents and planned outages occur.

In the absence of water, the pump runs dry. This is dry or idle.

If the pump is not turned off in time, it will overheat, which will lead to breakdown and costly damage. To add to the trouble that has happened, there will be a lack of water in the house for a significant period of time if there is no spare (backup) device.

In order to eliminate this situation, manufacturers produce models with protection against dry running of the pump. But they are more expensive than usual, so in some cases it makes sense to buy and install automatic protection separately.

Methods of protection

To ensure that a running pump automatically turns off when there is insufficient water in the source, you should use the following devices:

• automatic relay;
• water flow control device;
• water level sensor.

Each of these devices is capable of stopping the water supply (if there is insufficient quantity) to protect the pumping unit from overheating and breakdown.

Protection relay

A simple electromechanical element that responds to changes in pressure in the water supply system. When the pressure drops below certain value, the power electrical circuit automatically breaks. Power is not supplied to the pump and it stops working.

Structurally, the relay has a flexing membrane, which, when the pressure drops, changes its position and closes the circuit on the contact group, which leads to a power outage.

Depending on the manufacturer’s settings, the relay is activated when the pressure drops from 0.6 to 0.1 atmospheres, in the absence of water, insufficient water level or a clogged filter on the suction pipe.

In systems that contain a hydraulic accumulator, the relay will not be effective. This is due to the fact that usually, between the protection and the pump, a check valve, which maintains pressure due to the presence of water in the accumulator. And since the minimum pressure value for such a system is 1.4-1.6 atmospheres, the protection will not work even if there is a complete absence of water in the source, due to the fact that it is in the storage tank.

How to connect a dry-running relay to the pump (video)

Water flow control

Using a pump with dry-running protection involves including devices in the system that control water flow:

• relay (sensor);
• controller.

The former belong to the group of electromechanical devices, the latter are electronic.

Relays (sensors)

Manufactured in two versions:

The first ones are made in the form of a flexible plate, which, being in the pipe, is deflected under the pressure of moving water. In case of cessation (absence) of water movement, the plate aligns itself and closes the contacts to turn off the power to the electric motor.

The latter work on the principle of creating electromagnetic field turbine rotating in the water flow. When the number of electromagnetic pulses decreases, in case of weakening of the flow or its absence, the power to the pump is turned off, and when it increases, it is resumed.

Some inconvenience in using these devices is that they must be inside the pipeline. If solid particles (sand) get inside the system, interruptions in operation or their complete stop are possible, which requires partial dismantling of the water supply system.

Controllers

Devices that provide reliable protection pump electric motor against overheating, which, in some models, have an additional built-in check valve and pressure gauge. In fact, such devices are electronic relays that respond to changes in pressure in the water supply system.

The main functions are dry-running protection and fluid pressure control. The use of several parameters in operation leads to timely shutdown of equipment when there is a lack of water and maintenance of a stable operating pressure in the system.

The water supply system in which this device is included operates stably at any flow rate. water resources– when taps are opened or automatic household appliances are activated.

Level sensors

Water level sensors are installed directly in wells, boreholes, and tanks. They are used with both submersible (underwater) and surface (located above the water level) pumps.

According to the principle of operation, they are divided into two types:

• float;
• electronic.

Float

Designed to control the filling (to avoid overfilling of containers) or drainage (protection from running dry) of water sources.

Models of float switches are produced that operate in two modes, i.e. The pump is turned off when the water level drops or when there is too much water in a confined space.

The principle of operation is as follows: the sensor is placed so that the float is on the surface of the water at a set height. When the level drops, the float lowers, which is pivotally connected through a lever to the contact group. When a critical lowering occurs, the contacts of the phase wire open and the pump motor stops.

In the case of monitoring the filling of a container, everything happens the other way around. As the water rises, it also rises, the operation of which is configured not to lower, but to raise the level.

Electronic

Such devices perform the same functions as float devices, but their operating principle is different.

Into the source water or storage tank two electrodes are lowered. One to the minimum depth permissible level, the other to the working fill level (basic). Since water is a good conductor of electricity, the electrodes are connected to each other by low currents. The control device receives the signal and keeps the pump running. As soon as the currents disappear (when the water level drops below a critical level), the power supply is turned off, since there is no current-conducting material (water) between the electrodes.

The devices and methods of their use described above are suitable for protecting pumping equipment, monitoring water level and pressure in small systems for personal use. For a private home or cottage.

On large farms or apartment buildings, when installing autonomous water supply, for protection and control purposes should be used. Their cost is much higher, but when working with powerful pumping devices you cannot do without them.

Reliable operation of any devices is possible only if the conditions set by the manufacturer are met. It is especially important to adhere to this rule for those who work with devices that use mechanical components, for example, pumps. It is not advisable to operate most of them “dry”. Such expensive industrial and household equipment must have protection against dry running.

Dry running sensors

Reasons for installing protection

When it happens correct operation pump, then water flows through its cavity in a continuous flow. It performs several important functions simultaneously:

• the rubbing surfaces are lubricated, and the force to be overcome is reduced;
• During friction, heating occurs; heat is picked up by water flows and carried away from the friction area.

Excessive overheating without a pump dry-running protection relay leads to rapid wear and tear of the mating surfaces. The resulting heat when long work can deform working parts, sometimes irreversibly. The electric motor also receives excess heat, and if it is significantly overheated or there is no dry-running protection relay for the pump, it can burn out.

Hydraulic equipment with faulty dry-running protection sensors should not be allowed to operate.

Design features

Let's take a closer look at the dry running sensor for the pump and its operating principle. The dry-running protection relay is a block with several springs. It limits the operation of the entire device.

Everything is adjustable with a few nuts. The pressure force from the water is measured using a membrane. It either weakens the spring at low force or counteracts its resistance at high load. The principle of operation of the dry running relay comes down to a power load on a spring, which is capable of opening the contacts that supply voltage to the pump.

This protection against dry running of the pump during pressure reduction to the minimum indicated by the built-in algorithm closes the electrical circuit. With this action, the voltage on the electric motor decreases, and it automatically turns off itself. The pump remains sensitive to pressure increases. As soon as this works, the dry-running relay, according to its operating principle, will open the circuit and re-apply voltage to the motor.

You need to know that in most cases the relay on/off interval is from one to nine atmospheres.

Water level switch

Often pumps come with a factory setting of a minimum of 1.2 atm and a maximum of 2.9 atm, when they are completely turned off, without waiting for a drop to 1 atm.

Making adjustments

The direct mutual influence between the following quantities is derived:

• setting the pressure on the relay;
• hydraulic accumulator volume;
• water pressure.

When starting adjustment work, it is necessary to check the pressure level in the hydraulic accumulator.

The unit must be disconnected from the power supply and wait a few minutes for complete discharge capacitors. Water must be removed from the accumulator cavity. We also remove the cover on it and measure the readings on the pressure gauge, which should be about 1.4-1.6 atm. If necessary, increase the air pressure.

VIDEO: Automation for protecting pumps from dry running

Carrying out setup

The dry-running relay for the pump must be adjusted under pressure while the system is running. It is worth starting the pump first to pump the level up to desired value. The system will automatically turn off the power supply, as the relay will operate.

Adjustment work is carried out with a pair of screws located under the cover of the machine. To clarify the operation limits, you must perform the following steps:

• record the switching pressure;
• unplug the pump cable from the power supply;
• remove the sensor cover and slightly loosen the clamping nut of the smaller spring;
• the desired pressure parameter is adjusted by tightening/loosening the spring marked “P”;
• then open the tap, relieving pressure, and monitor the start of the electric motor;
• We record the readings on the pressure gauge, repeat the operation several times and derive the most optimal pressure values ​​empirically.

During adjustment work, it will be necessary to take into account the physical capabilities of the pump. With the nameplate value with all the losses, there may be a manufacturer’s limit of 3.5 bar, so we must go to 3.0 bar so that the pump does not burn out from overload.

High-quality protection against dry running

Operating a pump without water is the most common cause of breakdown of this equipment with normal power supply. A popular material for the manufacture of pumps is thermoplastic, which can withstand long-term use and is affordable.

During load without water, the rubbing surfaces warm up. This happens more strongly the more the device operates without liquid. A natural consequence of heating is plastic deformation, and almost immediately the motor jams and burns out from overload.

There are certain risk areas that are more likely to run dry:

• wells or wells with low water flow. The reason may also be excessive power of the device, which does not correspond to the flow rate of the liquid. During dry periods, the inflow per unit time also decreases at most sources;
• large containers serving as reserve collection tanks process water. Care must be taken to ensure that the pump does not operate in an empty cavity without liquid;
• network pipeline with an embedded pump to equalize the pressure in the system. During the dry season, there may be interruptions in water supply, leading to a drop in pressure.

External elements for protection

The following external elements are used as protection against dry running:

1. Float switch

The element relates to budget decisions. It is used to pump water from accessible containers. It only protects against overflow.

1. Pressure switch

Many devices have a contact opening when pressure thresholds are reached. Most of them have a low shutdown level and adjustment is not available in many models.

1. Flow switch with functions

If there is no water pumping through the relay, the power supply is automatically turned off. A small delay does not have a significant effect on the result.

Before purchasing additional protections, you should carefully read their threshold values.

VIDEO: How to protect the pump from dry running

Any electric pump that pumps water from a well or borehole functions normally only if there is a working medium. Water for this mechanism is both lubrication and cooling. If the pump pump unit will work idle, then after a few minutes it may become unusable. The dry running sensor for the pump is designed to monitor the presence of water flowing through the pump. At his command, the power supplied to the pump should be turned off in the absence of water.

So, dry running is the most common reason pump failure. Moreover, in this case it will be impossible even to carry out warranty repairs if the examination proves this reason breakdowns. This problem can happen in the following situations:

1. Incorrect choice of height for hanging the pump in a well or well. This can happen if the depth of the water container has not been measured in advance. When the pump pumps out water to the level of its location, it will begin to capture air, resulting in overheating of the electric motor.
2. The amount of water in the source naturally decreased. For example, the well (well) silted up or the water simply did not have time to get into the well after the last pumping. After completely pumping water out of the well, you must wait a certain time to fill the well.
3. If a surface pump is used, which is located on the water surface, then the reason for its failure may be different. There are frequent cases when the suction pipe of the pump loses its tightness. Water is sucked in along with air, resulting in the pump motor not receiving sufficient cooling.

So, if protection well pump If there is no dry running, the pump overheats and burns out. This applies not only to the electric motor. Modern pumps have a large number of plastic parts. Plastic, in the absence of cooling and lubrication, can also become deformed. This will first lead to a decrease in the performance of the device, and then cause it to overheat, jam the shaft and cause engine failure. Craftsmen are familiar with this type of failure, which occurs as a result of overheating. Having disassembled the unit, you can easily find those parts that have undergone overheating.

Types of dry running sensors and features of their operation

Expensive pump models already have built-in dry-running protection sensors. In particular, all pumps from the manufacturer Grundfos are already initially equipped with similar sensors. When using cheaper units, a dry running sensor for submersible pump have to be installed additionally. Let's try to understand the intricacies of the design and operation of dry running sensors of various types.

Water level sensors

1. Float switch. The connection diagram for the dry running sensor for the pump must be arranged so that its contacts are included in the power supply circuit of the pump motor. The float is afloat. When the water level drops, the float changes its location and its contacts automatically open, causing power to the pump to turn off. This is the simplest type of protection, characterized by reliability and ease of operation.

Tip: In order for the float to work on time, it must be adjusted correctly. It is important that the pump body is still immersed in water when the sensor is triggered.

2. Water level control sensor. Let's take a closer look at this dry-running sensor for a pump and its operating principle. This is a relay consisting of two separate sensors lowered to different depths. One of them is immersed to the minimum possible level of pump operation. The second sensor is located slightly lower. When both sensors are underwater, a small current flows between them. If the water level decreases below minimum value, the current stops flowing, the sensor is triggered and opens the power circuit.

Sensors that monitor the water level are good because they allow you to turn off the pump even before the unit body is above the surface of the water. Consequently, the equipment is reliably protected from damage.

Protection relay

This is an electromechanical device that controls the pressure of water flowing through the pump. When the pressure drops, the pump power circuit opens. The pump dry running protection relay consists of a membrane, a contact group and several wires.

The membrane monitors water pressure. In the working position it is open. When the pressure drops, the membrane compresses the relay contacts. When the contacts close, the pump turns off. The membrane operates at a pressure of 0.1-0.6 atmospheres. Exact value depends on the settings. A drop in pressure to this level indicates the presence of the following problems:

• The water pressure has dropped to its minimum value. This can happen for several reasons. Including loss of performance by the pump itself due to exhaustion of its resource;
• the pump filter is clogged;
• the pump was above the water level, causing the pressure to drop to zero.

The protection relay can be built into the pump housing or mounted on the surface as a separate element. If the water pumping system includes a hydraulic accumulator, then protective relay installed together with a pressure switch, in front of the hydraulic accumulator.

Water flow and pressure sensors

There are 2 types of sensors that monitor the passage of the working medium through the pump unit and provide protection against dry running of the pump. These are flow switches and flow controllers, which will be discussed below.

1. The flow switch is an electromechanical type device. They come in turbine and petal types. The principle of their operation also differs:

• Turbine relays have an electromagnet in their rotor that produces an electromagnetic field as water passes through the turbine. Special sensors read the electrical impulses generated by the turbine. When the pulses disappear, the sensor turns off the pump from power;
• Paddle relays have a flexible plate. If water does not enter the pump, the plate deviates from its original position, causing the mechanical contacts of the relay to open. In this case, the power supply to the pump is interrupted. This relay option is characterized by its simple design and affordable cost.

2. Flow controllers (automation unit, press control). These are electronic devices that simultaneously monitor several important parameters of water flow. They monitor water pressure, signal when its flow stops, and automatically turn the pump on and off. Many devices are equipped with . High reliability also determined the high cost of these devices.

Which protection should you choose?

Choose the right option protective device not easy. Several factors must be taken into account simultaneously:

• depth of water tank;
• well diameter;
• features of the pumping equipment used. For example, a submersible or surface pump is used;
• your financial capabilities.

For example, the simplest and cheapest means of protecting a pump from dry running is a float sensor. However, it must be taken into account that its use in a small diameter well is impossible. But for a well it is ideal.

If the water in the working container is obviously clean, then the most the best option will use a water level sensor. If you are not sure of the quality of the water supplied to the pump, it is better to use a flow switch or water pressure sensor.

Note: If there is a possibility that the pump filter is clogged with debris or dirt, then it is not advisable to use a level sensor. It will show the normal water level, although no water will be supplied to the pumping unit. The result will be a burnout of the pump motor.

A small conclusion can be drawn. You can use a pump without dry-running protection only if it is possible to constantly monitor the flow of water from a well or well. In this case, you can quickly turn off the power to the pump if the water stops flowing from the source. In all other cases, it is better to play it safe by installing a protective sensor. Its price is well worth it, considering the cost of purchasing a new pump to replace burned-out equipment.

Dry running is the incorrect functioning of a well pump for a water supply system, as a result of which liquid stops being pumped out. This mode of operation is unsafe because it can cause the equipment to malfunction at any time.

The borehole pump is designed so that the pumped water acts as a lubricant and cooling system in the device. If it does not reach the required level, the equipment may overheat. In case of operation in dry running mode for long term

the main parts of the device are damaged, as a result of which the pump motor may be destroyed.

For this reason, it is necessary to monitor the operation of the well pump during operation of water supply equipment. Dry running protection is achieved through system automation. Special thermostats, relays and float controllers will be able to turn off the equipment when dry running is detected.

Main factors of dry running The main factor in the incorrect operation of the pump is the lack of fluid. It makes no difference which source is used when pumping water. An artificial reservoir, a large container, a drilled well, a well - in each of the listed sources the water runs out and borehole device

appears above the liquid level.

Thus, the pump begins to run idle, and problems soon arise in it. This may be due to the fact that the equipment for pumping water was incorrectly selected or placed inside the well. To eliminate the possibility of idle operation, the installation of a well pump is usually carried out at the dynamic level of the well, that is, where the water never decreases.

Minor factors of pump idling are usually observed in equipment that is designed to operate from the surface of the well. There are often cases when pipes for pumping liquid become clogged, as a result of which water begins to flow poorly. Sometimes a pipe loses its seal due to damage or deformation. As a result, air penetrates the water supply system and gets inside its main devices, disrupting their operation. Mechanisms connected to the water supply system in country houses , most often installed as a water pressure amplifier. In this case, the idle operation of the device does not occur due to a lack of liquid, but due to low pressure in the centralized system

Based on this, we can say with confidence that dry running is manifested by similar factors, that is, it is associated with the loss of the necessary liquid or the presence of air in the water supply system. If the device operates only with human participation, it does not require defense mechanism. Its need also disappears in case of pumping water from permanent source, which may be a natural body of water. But if an automated water supply network is used, the pumping devices need constant monitoring and protection.

Dry running protection for the pump

To protect the water pumping system from idle operation, it is necessary to equip it with special thermostats and relays designed for automatic shutdown power supply when the pump overheats. Idle operation of a device can be detected based on three factors:

• well filling level;
• pressure forces on the outer pipe of the pumping mechanism;
• force of water pressure pumped out by a pump.

Float controllers and liquid level switches function by monitoring the degree of required height water.

Because the controller is placed above the fluid transfer equipment, it allows it to function. If this level drops below normal, the controller circuit will be disconnected, resulting in no power to the water supply. Most controllers will require manual connection of the pumping mechanism.

The relay is the most advanced technological solution. It contains 2 controllers located on the lowest and highest high levels wells. If a deviation from the norm occurs, the equipment turns off. In case of backfilling and reaching the required level, the mechanism begins to function again. The main advantage of the pressure switch is that the system is turned off before idle operation occurs.

The second factor is the pressure force on the outer pipe of the pumping mechanism. If the pressure drops below the established norm, this means that the equipment is not pumping out water. Accordingly, it needs to be disconnected from the power supply.

The third and final factor is the force of fluid pressure that is supplied through the pump via the flow controller. When the pressure level decreases, a critical point is reached, which causes the device to instantly shut down.

The second and third methods involve operating the pumping mechanism in idle mode for some time, since the controller must detect incorrect operation of the equipment in order to turn it off. Although this is a small drawback. It is worth considering that it will take at least 5-10 minutes for the mechanism to become faulty.

Protection of the water supply network from idle operation will be required in country houses, but in most cases it is not used alone, but in combination with automated mechanisms, the installation of which is determined by the implementation scheme water pipes and the presence of a water battery.

“Dry running” is a pump operating mode during which no water is pumped through the pump. This mode is extremely undesirable and emergency; it reduces the service life of the pump. The water pumped by the pump is both a lubricant and a coolant. Without it, the pump overheats; during prolonged operation in the “dry running” mode, the working elements of the pump can become deformed and the motor can burn out. To ensure long and reliable operation of the pump and all water supply systems in general, this should not be allowed. To protect the pump from dry running, automation is used: dry running sensors, dry running relays, float sensors, etc. They will turn off the pump when running dry.

Causes of dry running

The very first and most obvious reason is the lack of water. It doesn’t matter where the water is pumped from - a tank, a reservoir, a well, the water may run out, or its level will be lower than the position of the submersible pump (or the surface suction pipe). In the case of a well, this situation may mean that the pump itself is incorrectly selected and its productivity is greater, or its location is incorrectly chosen - it is located higher.

Other cases of dry running are typical for surface pumps: the water suction pipe may become clogged and water will stop flowing in the required quantity, or the tightness of this pipe may be broken, air will leak in and enter the pump.

For pumps that are connected to the water supply network (for example, in gardens or villages) to increase the water pressure in the home water supply network, dry running can occur not only when there is a complete absence of water in the centralized water supply system, but also when the pressure in it is low.

Thus, dry running has similar causes in all cases and is associated with a complete or partial absence of water and air entering the pump. In the very simple case When the pump is used only to supply water from a well or well and there is a person nearby when it is operating, there is no need for protection against dry running. There is also no need for it if pumping occurs from a known inexhaustible source, for example from a lake. But if you have an automated plumbing system, such protection is necessary.

Dry running protection for the pump

To protect against dry running, sensors and relays are used that turn off the power either immediately after dry running occurs, or in advance. Dry running is detected by determining one of three quantities:

1. water level
2. pressure at the pump outlet
3. water flow through pump

Float sensors and level switches work by monitoring the water level. located above the submersible pump (or above the suction pipe surface pump) and when the water level drops below it, it opens electrical circuit turning off the pump. Restarting the pump after the water level has been restored is most often done manually. A pressure switch is a more advanced tool that has two sensors located at the minimum and maximum water levels. When the water level drops below the minimum, the pump is turned off, and when it is restored to the maximum, the pump is turned on again (if necessary). The advantage of such devices is that they turn off the pump before it runs dry.

The second approach is to measure the pressure at the pump outlet. It is logical that if the pressure there drops below critical (usually considered 0.5 bar or less), then the pump has stopped pumping water and needs to be turned off.

And finally, the third option is to measure the water flow through the pump using a flow sensor. As soon as the flow rate drops below a critical level, the power to the pump is turned off.

The last two methods involve short-term operation of the pump in dry running mode: first dry running occurs, then the sensor detects this and turns off the pump. This can be considered a disadvantage, although in order for the pump to be damaged and fail in dry running mode, it must operate for several minutes (or even tens of minutes).

Protection of the pump from dry running is necessary in water supply systems of country houses, but most often it is not used on its own, but in combination with other automation devices, the installation methods of which depend on the water supply system, the availability