Automatic pumping station: implementation of protection against dry running. Dry running protection for pumping station

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 runs idle, it may become unusable after just a few minutes. 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 not even be possible to carry out warranty repairs if the examination proves this cause of the breakdown. 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. In the source naturally the amount of water has 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 large number 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 operating cheaper units, a dry-running sensor for the submersible pump must 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 the minimum value, the current stops flowing, the sensor is activated 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 separate element. If the water pumping system includes a hydraulic accumulator, then a protective relay is 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.

Example of a flow sensor
Such units turn off the pumping equipment if there is no water flow and turn it on if the pressure in the system drops below a predetermined level

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

Which protection should you choose?

Selecting the right type of protective device is not easy. Several factors must be taken into account simultaneously:

  • depth of water tank;
  • well diameter;
  • features of the used pumping equipment. 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.

The equipment installed in the water intake system is not cheap and requires professional installation skills. Required condition uninterrupted operation– well-organized protection of the well pump from dry running. The danger of working in dry mode lies in the difficulty of diagnosis: the device will stop working only after failure. The cost of restoration is comparable to the price of a new device, and in the event of a malfunction due to improper operation, the equipment is not subject to warranty repair; the manufacturer must indicate the working environment in the instructions. For this reason, it is recommended to install special protective electrical devices on all types of well pumps.

Well protection must be comprehensive. It is necessary to take into account all the main factors that can render the water pumping device unusable:

  • Water hammer: a sharp increase in inlet pressure. As a result of sudden pressure fluctuations, mechanical damage to the housing elements and impeller occurs.
  • Suspensions of solid particles. Poor filtration is the reason why small insoluble impurities get inside the device.
  • Dry run. The device works by pumping water. If air appears inside instead of water, the situation is fraught with overheating, deformation of parts, and loss of power.

Consequences of dry running: damaged impeller

Causes of breakdowns of well pumps

Situations when downhole equipment begins to operate abnormally can be caused by:

  1. Incorrect power calculation. The most common mistake is installing a powerful submersible device into a well with low flow rate. The device quickly pumps out a large volume of liquid, and the water does not have time to fill the container.
  2. Incorrect installation. If the pump is installed on insufficient depth, at the slightest drop in level there is a danger of dry running. If the device is lowered excessively, a situation may arise when the equipment sucks in sand along with silted liquid, and the inlet hole becomes clogged with dirt.
  3. Seasonal change in flow rate. Protection of well pumps will ensure correct operation in hot weather, when the water level drops and it becomes necessary to adjust the power of the equipment.

Dry running: what is dangerous and how to deal with the problem

Why is dry running dangerous for equipment? Model design submersible pumps provides for the use of water as a means of protection. Cold liquid cools internal surfaces mechanism, provides working pressure. In addition, for equipment used at depth, it is not possible to organize a classic system for lubrication of rubbing parts: this function is also performed by water. The result of even short-term operation in dry mode is overheating, deformation of parts, and engine combustion. To protect the equipment, it is necessary to install devices that immediately turn off the pump when the water supply stops.

How to choose the right mechanism to protect against dry running

Protection of a well pump from dry running must be selected taking into account the type of equipment and characteristics of the well. Manufacturers offer systems for wells, general centralized pipelines, and wells of different depths. Experts also recommend taking into account the performance of the source and the power of the pump. The specifics of the well design can significantly limit the choice: pipe diameter, location and type of pumping equipment. Definitely worth getting a consultation experienced specialist before purchasing and installation.

Ready solutions with pressure sensors

Types of devices and features of their application

All electronic protection systems operate according to general principle: turn off the pump if there is a danger of dry running or if a lack of water is detected inside the device. After the water level normalizes, the equipment starts up as usual.

Device types:


Self-installation or professional installation: is it possible to save money?

It is better if the well protection is thought out and organized before the first start-up of the equipment. In this case, it is possible not only to prevent equipment malfunctions, but also to promptly identify mistakes during well construction and equipment installation.

The choice of a system that will reliably protect an expensive device should be entrusted to a specialist. It is difficult to take into account all the criteria on your own. The wizard will help you determine the type of system that is optimal for specific conditions.

You won't be able to save on self-installation: the process requires preliminary calculations. Some systems involve intervention in the design and power supply system of the device, so it is better if the installation is carried out by a qualified specialist.

Video: how to protect the pump from dry running

A common cause of failure of submersible pumping equipment and superficial appearance the fault is the idle speed. Regardless of the material of manufacture, in the absence of water in the unit, parts become deformed and the engine overheats.

Failure due to dry running is not covered by the warranty period, since the passport for the pump always indicates the inadmissibility of idle operation. Repair of such cases entails additional financial costs.

1 What is dry running?

Dry running is the process of operating injection equipment in conditions of absence or insufficient flow of water, which serves as a lubricating and cooling material for parts.

In the absence of water, parts become deformed and overheated and, as a result, the engine burns out. Due to engine combustion, the equipment fails.

1.1 In what situations does idling occur?

During operation, it is not always possible to monitor the operation of the pump. Therefore, you should be aware of the most common cases of the problem:

  • when pumping water from a container. When the reservoir is empty, the unit continues to run dry. When performing such work, it is necessary to control the process and turn off the device without waiting until the container is empty;
  • transportation of water from wells. When using a pump with increased capacity in summer period. In the summer, if there is no rain, the water level in the wells drops, so there is a shortage of water. When the water level is low, the pump will run dry;
  • operation of devices for increasing pressure in the pipeline. In the city highway of multi-storey buildings, lack of pressure becomes the cause idle speed pump

Dry running can be prevented with special devices.

2 Devices for protecting pumping units

There are several devices for idle protection:

  1. Pressure switch with protection. The device has an additional function in the form of protection. Used when connecting pumps directly to the pipeline. In a relay, the contacts open when the pressure drops below a certain level. The level is determined by the manufacturer and is 0.6 Bar. Pumping equipment is operated under pressure conditions of one bar. The pressure drops below this limit when there is no water. If there is no water, the contacts open and the pump turns off. The disadvantage of this method is that the pump can only be turned on manually; to do this, you will have to refill the device with liquid. This method is used in conjunction with a hydraulic tank and automatic operating mode. Installed together with submersible, surface units and pumping stations.
  2. Press control It is recommended to install it instead of a hydraulic tank or pressure switch. Thanks to the device, the pumping equipment turns on when the pressure drops to two and a half bar. If there is no liquid passing through the flow switch, water suction stops and the device turns off. The relay protects against dry running of the pump by registering the passage of liquid through the relay. The advantage of the method is additional function in the form of current and voltage protection. The device is lightweight and small in size. In the flow part of the device there is a float with a magnet or a spring check valve. The fluid flow displaces the valve, at which point the contacts close. When the liquid supply stops, the valve goes into starting position, the float lowers and the contacts open, the pump turns off. The shutdown occurs with a time delay. The delay is necessary to reduce switching on and off at low fluid flow. This is due to the absence of an upper pressure limit for shutdown. And the pressure corresponds to the pressure level. And the unit turns off when there is no pressure. To prevent you from purchasing a low-quality device, you must buy a device at a price of one hundred dollars or more. Then you won’t have to change the device after a year. The advantage of the device is small sizes and protection against water hammer thanks to the intermediate tank.
  3. Float used when transporting liquid from a container or well. It has a low price. There are two types of float switches. The first one is triggered when the container is full. Opening occurs when the container is filled with liquid to a certain point. When the contacts open, the pump turns off. This type of device prevents the tank from overfilling. The second type turns off the pump by opening the contacts when the liquid reaches a minimum permissible value. Limit level is set by installing a float in in the right place. The device wire is mounted in such a way that when the water level drops and, accordingly, the device is lowered, there is still liquid in the container. When using a surface or submersible apparatus, the device is placed so that the water is above the valve of the apparatus when the contact is opened. Some types of pumping equipment are manufactured with built-in floats, the level of which can be adjusted depending on need. This type of idle protection comes in two types: heavy and light. The lightweight type is used in water supply and sanitation. The heavy type is used for fecal, drainage systems. According to the length of the cable, they are divided into two, five and ten meters. The disadvantage of this method is that it cannot be used in wells and pipelines. There is also a limitation on the diameter of the well, which is at least forty centimeters. For this reason, this type of protection is not universal.
  4. Level relay consists of an electronic type board with three electrodes. One carries out control, two works. The function of the sensors is to send a signal. The sensors are immersed into the well at different heights. The control sensor is installed above the pump level. When the liquid level decreases, the signal from the sensor enters the level relay, which turns off the pump. When the liquid level rises above the sensor, the pump turns on. When the sensor is immersed, the contacts are closed and the pump operates. The shutdown delay time is set by a special potentiometer located on the front panel of the relay. When setting, it is necessary to take into account that the position on the left is the minimum delay, and on the right is the maximum. When the delay time has passed, the device turns off. The unit turns on when the water reaches the sensor. This type of protection is used in single-phase pumps with a power of one and a half kW. To be able to combine it with a single-phase pump of higher power or with a three-phase pump, a magnetic type starter suitable for power is used.

When designing fluid transport systems special attention it is necessary to pay attention to protecting the pump from “dry running”. This problem can be solved in various ways. In some cases it is necessary to install additional sensors, in others - electrical devices.

What is “dry running”?

“Dry running” is a pump operating mode in which no liquid (usually water) is pumped through the pump. This can happen if the tank runs out of water, the tank leaks, all the water is pumped out of the well, etc. “Dry running” is very dangerous for the pump, because liquid performs a series useful functions for the pump, one of them is cooling. If it runs dry, the pump may overheat and fail.

To prevent breakdown of an expensive pump, it is necessary to provide protection against such a phenomenon as “dry running”.

All methods of protection can be divided into two groups.

1 Protection against “dry running” by monitoring the physical parameters of the liquid in the pipeline:

  • water level control;
  • pipeline pressure control;
  • control of water flow in the pipeline.

The essence of all these methods is that the sensors detect a decrease in level, a drop in pressure, a decrease in flow and issue a signal to turn off the power to the pump.

Disadvantage: they require installation of sensors on the pipeline (in a container).

Dignity: high reliability protection.

2 Protection against “dry running” by monitoring the electrical parameters of the pump supply network.

During “dry running,” a change in the electrical parameters of the pump occurs. By controlling the necessary parameters, you can perform dry-running protection.

The electric motor driving the pump can be considered in itself as a “dry running” sensor.

In normal mode, the power factor (cos) of the pump is 0.7-0.8, but when “dry running” occurs, cos drops to 0.3-0.4. Thus, to monitor “dry running” you can use a power factor control relay. For example, G2CU400V10AL10 manufactured by the Austrian company TELE.


The power factor relay analyzes the voltage and current that the motor draws and, based on this information, calculates the power factor (cos). The current sensing input is designed to directly measure current up to 10A, so if rated current motor is more than 10A, then the G2CU400V10AL10 relay must be connected via a current transformer.

More details about the operating modes and connection diagrams of the power factor control relay G2CU400V10AL10 can be found in technical documentation, which is available at the link below:


Here is what the manufacturer of these relays answered to some of my questions:

The cosine phi drops instantly in the absence of water, but the relay will turn off the pump after the time you set: set a second - it will turn off after a second, set it to 30 seconds - it will turn off after 30 seconds.

Yesterday I went to production, there was a pump with a 7.5 kW motor, they set the setting to 0.7 - the water pump worked, they set it up to run dry... at the set point of 0.7, the relay detected a dry run.

The relay is installed in the power panel and does not require additional sensors.

Using a power factor control relay, you can get enough good protection from "dry running".

In one of the projects I used a current relay to protect a pump. It’s hard for me to judge how reliable this protection is, no questions were asked, apparently everything works. The essence of this method of protection against “dry running” is that when dry running, the current consumption also changes. We set the required current range on the current relay and thus turn off the pump when the current goes beyond the set limits.

In my opinion the most in the best possible way is to install a power factor control relay.

The most common emergency situation associated with the failure of a household or pumping station for home plumbing, this is the operation of the unit idling, that is, without pumping water or pumping with low pressure. This situation is called “dry running”. It should be noted that this type emergency situation is not covered by warranty. Because this is not the manufacturer’s fault, and he is not responsible for it. Improper operation of the pumping station is to blame.

Why is dry running dangerous?

During idle operation, a so-called zone of stable cavitation occurs. That is, under the influence of emerging elevated temperatures, changes in the design of some components and parts of the pump occur. That is why the term dry-running protection for a pumping station is increasingly heard.

Deformed impeller pump

The thing is that the pumped water is a cooling medium for such parts of pumping equipment as the impeller (impeller), sealing cuffs and guide devices (nozzle, inlet pipe). By the way, it should be noted that the impeller is a rather expensive part, and replacing it is not so easy. It is very important to understand that the impeller itself is located in separate compartment. And the gap between its edges and the compartment body is not very large. When thermally loaded, the impeller expands and begins to come into contact with the housing. This is an emergency situation. By the way, it is this that can damage the electric motor, which is much worse and more expensive.

Therefore, regardless of the device local water supply purchased as a whole or, it is recommended to install a dry running relay. An exception may be in some cases: when the pump operates intermittently, for example in a country house, when constantly monitoring the device, water is drawn from inexhaustible source, the consumer has extensive experience in operating the device. But even in these cases, many experts still recommend installing a safety relay to completely eliminate the possibility of breakdown.

Reasons

If we talk about external reasons appearance of dry running, then we can say that there are quite a lot of them. But they are all concentrated on one thing - the complete or partial absence of water in the working compartment of the pump. As for the partial absence, as a result of this, inside working chamber air bubbles appear. It is in them that zones are formed elevated temperature. Experts note that the critical performance of a pumping station, at which we can talk about dry running, is 5 l/min. What can affect this?

  • Lack of water in a hydraulic structure.
  • Depressurization of the supply hose or pipeline, due to which the pump inside the system begins to suck in air.
  • The check valve is clogged.
  • The voltage in the power supply network has dropped.

Pump parts after dry running

By the way, it should be noted that friction of rotating parts leads to an increase in temperature. This is from the course school curriculum in physics. Insufficient quantity water that flows inside the working chamber of the pump causes it to boil. It’s good if the impeller is made of metal, but today many manufacturers have switched to plastic, which reduces the cost of the product. But exactly polymer material reacts negatively to saturated steam, which deforms the plastic impeller.

Purpose of the dry running relay

As you can see, an emergency situation can lead to irreparable losses. The pumping station not only stops working, but after long-term operation in dry running mode it simply breaks down. After which you will have to do either expensive repairs or complete replacement unit. To prevent this from happening, manufacturers began to install a dry-running relay for the pumping station in the design of the device. Its main task is to turn off the power to the pump motor if the water pressure in the supply pipeline drops below critical. That is why the device is mounted on the pipeline after the pumping station.

Attention! The dry-running relay is not installed separately from the pressure switch. Both devices complement each other, working in pairs.

Dry running relay installation location

However, it should be noted that a dry-running relay is just a device that responds to a certain signal coming from some sensor that responds to changes in water parameters within the local water supply network. For example, protection against dry running of a well pump consists of a relay and a float switch. The latter monitors the water level in the hydraulic structure and sends a signal to the dry running relay, which interrupts the supply of electricity to the pump motor. Instead of a float switch, you can use a fluid flow sensor to monitor the speed of water in the pipeline. That is, you can always find a specific option that would track specific parameter water and reacted to its change.

Relay operating principle

Currently, manufacturers offer various models of dry running relays. But they all work on the same principle. In principle, this device works like a regular two-pin relay. That is, it is an intermediate device between the power supply network and the device that consumes electricity. Latest in in this case the pump of the pumping station acts. Therefore, the relay itself is installed in the network in series.

LP-3 device

This is how the Italian model Italtecnica LP3 works.

  • In the initial state, the relay contacts are always open.
  • To turn on the pump, you need to press the red button on the relay body and hold it in this state for a while.
  • That is, the contacts close, through which electric current begins to flow to the electric motor.
  • As soon as the pressure in the water supply network drops to 0.5 bar, the contacts simply open.

Attention! The presence of water in the water supply system creates conditions for its splashing. Therefore, all dry-running relays, regardless of the manufacturer’s brand, are manufactured with electrical safety requirements. Therefore their class electrical protection– IP44.

To respond to pressure in the water supply, a spring is installed inside the relay, which is adjusted to certain low and high critical values ​​of a given water parameter. It is with its help that the contacts inside the device are opened and closed.

Installation method

How to install correctly

As mentioned above, a dry running sensor for a pumping station is installed in conjunction with a pressure switch and mounted on the supply pipeline.

  • First of all, it should be noted that the entire installation process is carried out with an empty pipeline and pumping station.
  • The dry-running relay itself must be connected to the water supply line through a fitting, usually a tee. Installation must be carried out according to all plumbing standards, that is, with complete sealing of the joints.
  • It is very important to make the electrical connections of the devices correctly. As already mentioned, in this system the connection must be serial. By the way, this is clearly visible in the photo below.
  • All that remains is to connect the wires through the terminal box (contact group), which must be routed through the sealed leads. It is clear that working with electrical wiring Only necessary when the power to the unit is turned off.

Scheme electrical connection dry running relay

It should be noted that the diagram shown above is not standard. That is, it is not necessary to install a dry-running relay before the pressure switch. These devices can be swapped. The main condition is the sequential installation of both in the electrical supply circuit. Moreover, many models of pumping stations are already equipped at the factory with a pressure switch, which is installed directly at the outlet supply pipe of the pumping unit.

New generation relays

Currently, manufacturers have begun to offer new devices that include a check valve and an electronic plateau. But the control of the device is based on a micro switch and a magnetic relay. The latter are contacts sealed in a glass tube, but they respond well to a changing magnetic field.

A permanent magnet is installed on the check valve, which is spring-loaded. As pressure increases, the valve moves to the side glass flask, where under the influence magnetic field contacts close. That is, the circuit is closed and current is supplied to the pump motor. As soon as the pressure in the pipe drops, under the action of a spring the valve moves back, dragging the magnet along with it. That is, contacts open inside the flask. This opens the power supply to the motor, which immediately stops, interrupting the dry running of the pumping station.

New generation relays of the Brio series

This dry-running relay model has several useful options.

  • In order for the check valve with a magnet to connect the relay itself, it is necessary to create pressure inside the pipeline. Therefore, the electric motor starts without a relay, the operating time is 7-8 seconds. It is during this time that he can pump water into the water supply network to create pressure.
  • After the water supply stops, that is, the formation of a dry run, the relay turns off. But after a certain time it will turn on automatically. And if there is no pressure, it will turn off again. And this can be repeated several times. If after all attempts the water pressure is plumbing system did not increase, the relay switches off completely. You can only restart it manually.

This is how the dry running relay works, which protects pumping stations from emergency situations associated with the lack of water in the water supply system. A small device that increases the duration of trouble-free operation of pumping units.



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