Dry running protection for a pumping station. Reliable protection of a borehole pump from dry running: sensor selection and connection diagram Dry running pump connection diagram

The working process of water pumps is associated with numerous threats to the structure. These include pollution, engine overheating, breakdowns due to violations in the connections, etc. But even the correct organization of the operational process in accordance with the instructions does not guarantee the elimination of indirect threats. Dropping the pumped water level below the minimum value can lead to equally serious damage. To prevent this from happening, manufacturers recommend using a dry-running sensor for the pump, which captures the critical level of the working environment and decides to turn off the equipment.

General principle of operation of the device

Most protective devices of this type are associated with control automation. The controller fixes the operating parameters for subsequent correction of the supply volumes, turning the unit on or off. In this regard, dry or idling sensors are only one of the signaling devices about the state of the working environment. Determination of water shortage can be made different ways depending on the type of dry running sensor used for the pump. The principle of operation of devices such as pressure gauges, for example, is based on fixing the pressure level. When the threshold level is reached, the detector sends a signal to the controller, which, in turn, automatically turns off the pumping equipment. Moreover, the sensor can continue its work as a pressure gauge. And when a sufficient pressure level is restored, it also resumes the pump function via the control controller. Again, the signs of water shortage can vary.

Multifunctional relays are connected to several types of detectors, which increases the accuracy of determining the level of the serviced medium.

Dry running sensor classifications

The simplest systems of this type provide protection, guided by the readings of mechanical signaling devices. These are models of float and flow type, which can be directly structurally related to the target equipment. For effective work such devices, even the introduction of automation is not necessary. Most often, mechanical protection is used for well pump. In this case, the dry-running sensor should not even determine the critical level of shortage of the pumped medium, but its approach to the place of intake. For example, optimal height water column at pumps downhole type averages 150-200 cm, and a drop to 100 cm will be a critical point. Automatic systems, as noted above, involve control through automation. The control relay cuts off the power supply and the equipment stops. But in both cases, the principles for determining the parameters of water supply may be different.

float switches

Such models are widely used in equipment that pumps water from wells, storage tanks or drainage systems. When the water level drops at the point of intake, a short circuit occurs and the sensor turns off the power. This occurs in parallel with the lowering of the float detector connected to the contacts in the phases of the power supply system. If we are talking about submersible systems, then the sensor for protecting the pump from dry running is located above the protective grate of the nozzle or the bottom valve. The device can be integrated optionally, or, in the basic design, be part of the pump.

Flow switches with pressure sensors

AT this case press control is implemented. The normal mode of operation of the control system fixes temperature regime and pressure readings. The second parameter is treated as target value to determine the risks of idling. By default, press control is set to a standard value of 1.5-2 atm. This is the threshold level, the achievement of which turns the system on or off, depending on the dynamics to increase or decrease. Of course, the user can set the dry running sensor for the pump to other peak values, taking into account the characteristics of the equipment and the conditions of the water supply in general. Some models of downhole units with such controllers do not provide automatic switch on. After stopping in the operating mode, they are entered only manually if the water level has risen to an acceptable level.

Level sensors

The principle of operation of electrical liquid level meters is most common in industry. Such devices are used to accurately control the level of technical media in production tanks, and recently they have also been used in plumbing.

How does the dry running sensor work for this type of pump? The control relay includes an electronic board and several electrodes. Sensing elements are installed at different points of the tank in which water is pumped out, and during operation they exchange signals with each other. The liquid acts as a conductor for low-frequency currents, so the termination of communication will mean that there is no water on sufficient level. When the signal is interrupted, the circuit is opened and the power is turned off.

What to consider when choosing a sensor?

Beyond the definition suitable principle operation of the device, it is important to consider the conditions in which it will be used. The control unit itself can be installed in technical room. It does not have to be immersed in the working environment. But the sensor should be selected with an emphasis on temperature range and risks of physical damage. As for the first parameter, the spectrum from -1 to 40 ºС is considered optimal. In case of circulation pumps can be served and hot water, so the upper temperature bar increases to 70-90 ºС. From the point of view of the workflow, the pressure range that the dry-running sensor for the pump in a particular system can in principle be able to control is important. This indicator varies on average from 0.5 to 3 atm, and some versions reach a maximum of 10 atm. The protection class is also taken into account. The optimal solution for home use will be a model marked IP44.

Dry running relay connection

Installation of control valves is carried out at the stage of assembly of the pumping structure. First of all, a non-return valve with a filter is mounted on the suction line, after which it is possible to proceed with the integration of the protective relay. Again, the controller and sensors are located at different points. The main thing is that physically the moment of registration of the critical level is ahead of the start of idling.

The electrical connection of the dry running sensor for the pump is carried out in the following sequence with power from 200 V: socket - relay - pressure gauge - engine. Wiring loops usually operate with a current of about 10 A, while you should not forget about grounding and installing a stabilizing fuse.

Controller setup

The electrical circuit after installation will be an open two-contact relay. In this state, the pump cannot be started, as it will start to function at the same idle speed. Initially, the accumulator should be filled with water until the pressure reaches the optimum level. For this technological period, the dry running sensor for the pump must be activated. The principle of its operation at this stage is adjusted to the service mode, in which idling is allowed, but without an alarm, followed by shutdown of the equipment. When the accumulator is able to maintain sufficient pressure, the relay with the sensor is switched to normal operation. But before that, you should also set the threshold pressure value at which the electrical circuit will open again.

Pump controller manufacturers

High-tech relays with automation and the ability to prevent dry running are produced by Sturm, Elitech, Metabo, etc. The most successful developments come from the direct pump manufacturers. For example, Grundfos is working on a combination of centralized control panels, which include water fittings and a multifunctional package of protective automation. Domestic developers of controllers also succeeded in this direction. The dry running sensor of the Whirlwind 68/4/4 pump, for example, is distinguished by the support of a switching current of 12 A and maximum pressure at 10 atm. Its features include a high protection class - IP65. Worthy offers in terms of price and quality are also produced by Belamos, Dzhileks and Zubr.

When should you not use dry run protection?

Not always the additional load in the form of sensors justifies itself. Obviously, pumping water from a lake, reservoir or pond does not involve the risks of dry running. Another thing is that a change in the position of the equipment itself can lead to a shift in the level of water intake, but such problems should be solved by a more reliable installation. It is also not recommended to use a pump controller in high flow wells. The dry running sensor in this case simply will not work, wasting energy in vain. At the very least, for wells and wells, a seasonal schedule can be established, when the risks of a sudden change in water level rise and fall. Accordingly, for these periods it is necessary to adjust the operating mode of the control equipment.

Finally

It is also not worth underestimating the consequences of idling for pumping equipment. For some models, long-term operation in this mode will make itself felt in the form of breakdowns of individual consumables, which can be replaced with minimal cost. But there are also whole groups of units that are directly dependent on water supply. In modifications with rotary units, the pumped liquid can be used as a technical lubricant or coolant. Therefore, a dry running sensor for the pump can prevent very significant engine damage. For the same reason, the manufacturers themselves in the basic configurations increasingly provide for the presence of control equipment. Moreover, refusal to use protective devices is a condition for the loss of warranty, since the instruction manual for the equipment is violated. These nuances should be taken into account even when developing a water intake scheme, evaluating the possibility of connecting the most effective means control.

Modern pumping stations are often equipped with either a full-fledged dry-running protection, or at least protection against engine overheating. The benefit of having such elements in the design is obvious: where necessary, protection can prevent pump failure.

But the presence of protective modules leads to an increase in the cost of the structure. That is why it is worth considering in advance how important dry run protection is for you, and whether it is worth spending money on a more expensive station - such as.

The presence of a device that will turn off the pump when water stops flowing into the system is highly desirable in such cases:

• The pump is used to increase the pressure by tapping pumping station to the mains water supply. This is done quite often, and in order to insure the equipment in case of a water supply shutdown, protection is installed.
• The station is used to draw water from a reservoir. Here, the relevance of protection against “dry running” is obvious: as soon as the container is emptied, the pump will begin to “grab” air, and if it is not turned off in advance, it will quickly fail.
• As a source autonomous water supply a well or a well with a low debit is used. Here, too, there is a risk that the hose with which the intake is carried out will be above the water level, and this will lead to breakage.

The latter case is relevant for almost all private households. AT summer time the water level is already falling, but it is additionally lowered due to intensive selection for irrigation. So a pumping station pumping water from a well or shallow well, necessarily tedious to protect.

Ways to implement protection

Dry running protection can be implemented in different ways. Here are the most common patterns.

float switches

A float is the simplest device that is used when equipping autonomous water supply systems based on tanks or wells:

• The float is fixed in such a way that the system works when the water is just above the level of the intake pipe.
• When the water level drops, the float opens the contacts.
• When the contacts open, the phase supplying the pump is broken, and the pump stops working.

Pressure/flow switch

Another device (example -), which is equipped with many pumping stations. It works quite simply:

• The manufacturer sets a certain pressure level at which the relay is activated. Usually this value does not exceed 0.5 -0.6 bar and cannot be changed by the owner of the pump.
• As soon as the pressure in the system drops below this level (and this does not happen even with intensive simultaneous water withdrawal), the relay registers a “dry run” and the pump is de-energized.

Note! Restart must be carried out in manual mode, after the cause of the relay operation has been eliminated and the system has been filled with water.

A prerequisite for the effective operation of the pressure switch is the presence of a hydraulic accumulator. However, automatic alluvial stations are completed initially.

If there is no accumulator, then a compact flow switch can be used instead of a pressure switch. But it works on a similar principle, but turns off the system when water passes through the device. The response time of such devices is short, so the pump receives effective protection.

Level switch

If the water source is a well, then a level switch can be used to protect the pump from "dry running":

• The relay is a board to which the electrodes are connected (usually two working and one control).
• The electrodes are lowered into the well and fixed in such a way that the control electrode is located just above the level of the well pump installation.
• As soon as the water level in the well drops, the control sensor is activated and the pump is turned off. After the water level rises, the system automatically starts on a relay signal.

To begin with, let's go over the theory, answer the question: “why do you need a dry-running protection relay for a borehole pump?”, And then we will consider the principle of operation and how this relay is connected.

Dry running of the pump is a condition in which the pump runs empty, without water. In this state, the pump quickly overheats and can fail in a matter of minutes. To provide safe work pump, a dry-running protection relay was invented.

Let's take a quick look at what can cause a pump to run dry:

1. When the pump power is incorrectly selected - for example, a pump with a high capacity is selected, which pumps out all the water from the well.
2. When the water level in the well naturally dropped.
3. Water pipe leakage.

The principle of operation of the dry-running relay

Now let's look at how the dry running relay works. If we disassemble the relay, then under the cover we will see: a safety button, a group of normally open contacts to turn off the pump and two springs for regulating the shutdown pressure.

When water disappears in the water pipe, the pressure in the water supply system drops sharply. At this moment, the relay, under the action of a spring, opens the contact group, which in turn turns off the supply electric current to the pump.

The relay is reactivated by pressing the safety button. The contacts are closed, thereby the circuit for turning on the pump is assembled, which creates the necessary pressure in the system, is in the range of 1 - 1.5 atmospheres. At this pressure in the system, the contacts of the dry-running relay will be permanently closed.

Relay adjustment

At the factory, the dry-running relay is set to a pressure of 0.5 - 0.8 atm. At this pressure, the contacts open and turn off the pump.

Consider the process of adjusting the shutdown pressure using the example of the LP / 3 relay. To do this, you need to do a number of operations:

1. Disconnect the pump from the power supply.
2. Open the protective cover of the relay.
3. On the small spring, tighten the nut clockwise, thereby increasing the initial switching pressure.
4. On the big spring, Tightening the nut clockwise will raise the pump shutdown pressure.
5. After adjusting the relay, we need to determine the shutdown pressure: for this, it is necessary to analyze the water in the system, for example, open a tap in the sink, as the water supply system is empty, the water pressure will decrease. On the pressure gauge, track at what pressure the relay contacts open. There should be a click and the safety button will pop out of the housing.

Through such simple manipulations, we can set the shutdown pressure we need.

How to connect a dry running relay

The dry-running protection relay is mounted in the water supply system through the so-called five-pin, this is a fitting that has five connection pins:

1. Water supply to the system
2. Exit to hydraulic accumulator
3. Gauge output
4. Output for connecting a dry-running relay
5. Water outlet to the system.

This can be clearly seen in the following figure:

Since the dry-running relay is paired with pressure switch then circuit diagram The connection of these relays is as follows.

A dry-running protection relay is mandatory for installation, as it guarantees long term pump service. In case of failure of the pump due to dry running, it is considered not guaranteed!

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A dry running sensor is required in water supply systems to protect the pump from running without water. occurs when its suction pipe is above the water level. This can happen when the tank from which the pumping occurs is empty, or when the water level in the well or well drops. Sensors detect dry running and turn off the pump before it fails.

AT electrical circuit the sensors are connected in series with the pump and, when a dry run is detected, they open the circuit, turning off the power. The circuit diagram of the connection is shown in the figure.

To detect dry running, the sensors measure one of three quantities:

1. The water level where the pumping is from

2. Water pressure at pump outlet

3. Water flow from pump outlet

Dry running float switch

Dry running sensors that measure the water level are most often. They are placed so that at a critically low water level the float is in the lower position and thereby opens the electrical circuit.

The dry running sensor can use a pressure switch to monitor the water pressure at the pump outlet. Such a sensor can be installed either directly after the pump (usually 1 m from its outlet), or in front of the accumulator at the beginning of the house's plumbing system. When using borehole pumps, it is impossible to place such a dry-running sensor inside the well, so it is already placed on the surface. The essence of the operation of the sensor based on the pressure switch is that when the pump runs dry, the water supply stops and the pressure drops. A drop in water pressure below critical (usually below 0.5 bar) can only mean one thing - there is no water. The dry-running relay is activated and the pump turns off as soon as it starts to run dry.

Connecting a pressure switch in front of the pump - that is, on its suction pipe - will not give the desired result, because when sucked, the pump creates a vacuum, and the pressure there will be zero, which will trigger the dry-running relay.

The action of the dry-running relay is based on a flexible membrane, which is distorted under water pressure, and, due to this, the contacts are closed. If the pressure drops so much that the membrane straightens, then the contacts open.

A dry-running sensor based on a flow switch measures the water flow at the outlet in the same way as a pressure switch. If the water supply stops while the pump is running, this means that the pump has started to run dry and the flow switch cuts off the power.

Read also:

• "Dry running" is a pump operation mode during which no water is pumped through the pump. This mode is extremely undesirable and emergency, it reduces the life of the pump. The water pumped by the pump is both a lubricant and a coolant. Without it, the pump overheats and fails.
• A float switch is a device for automating the operation of pumps in water supply and sewage systems of private houses, the essence of which is that it turns the pump on or off at a certain water level.
• This article will consider a typical diagram for connecting a hydraulic accumulator to submersible pump and private water supply system country house. The source of water can be a well or a well, a hydraulic accumulator is used to provide an acceptable on / off mode for the pump.

A common reason for the exit of submersible pumping equipment and superficial failure is idling. Regardless of the material of manufacture, in the absence of water in the unit, parts are deformed and the engine overheats.

Failure due to dry running is not eliminated at the expense of 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 a dry run?

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

In the absence of water, deformation and overheating of parts occur and, as a result, combustion of the engine. Due to the combustion of the engine, 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 tank. When the tank 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 an overestimated capacity in summer period. In the summer, when there is no rain in the wells, the water level drops, so there is a lack of water. When the water level is low, the pump will run dry;
• operation of devices for increasing pressure in the pipeline. In the urban highway of multi-storey buildings, the lack of pressure causes the pumps to idle.

Dry running can be prevented by special devices.

2 Protection devices for pumping units

There are several devices for protection against idling:

1. Pressure switch with protection. The device has an additional function in the form of protection. Used when connecting the pump directly to the pipeline. In a relay, the contacts open when the pressure falls below a certain level. The level is determined by the manufacturer and is 0.6 bar. Pumping equipment is operated under pressure from one bar. The pressure drops below this limit in the absence of water. In the absence of water, the contacts open and the pump turns off. The disadvantage of this method is that it will be possible to turn on the pump only manually, for this you will have to refill the device with liquid. This method is used in combination with a hydraulic tank and automatic operation. It is installed together with submersible, surface units and pumping stations.
2. Press control recommend installing instead of a hydraulic tank or pressure switch. Thanks to the device, pumping equipment turns on when the pressure indicator drops to two and a half bar. If there is no passage of liquid through the flow switch, the suction of water stops and the device turns off. The relay provides protection against dry running of the pump by detecting 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 differs in the small weight and the sizes. 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 fluid supply stops, the valve returns to its original position, the float drops and the contacts open, the pump turns off. Shutdown occurs with a delay in time. The delay is necessary to reduce cut-in and cut-outs at low fluid flow. This is due to the lack of an upper pressure limit for shutdown. And the pressure corresponds to the pressure level. And the unit turns off in the absence of pressure. To prevent the purchase of a low-quality device, you must buy a device at a price of one hundred dollars. Then you do not have to change the device after a year. The advantage of the device is its small size and protection against water hammer due to the intermediate tank.
3. Float used when transporting liquid from a tank or well. Is different low price. There are two types of float switches. The first is triggered when the container is full. Opening occurs when the container is filled with liquid up to a certain level. When the contacts open, the pump turns off. This type of device prevents overfilling of the tank. The second type turns off the pump by opening the contacts when the liquid reaches the minimum allowable value. The limit level is set by mounting the float in the right place. The wire of the device is mounted in such a way that when the water level drops and, accordingly, the device is lowered, there is still liquid in the tank. When using a surface or submersible device, the device is placed so that the water is above the valve of the device when the contact opens. Some types of pumping equipment are made with built-in floats, the level of which can be adjusted depending on the need. This type of protection against idling is of two types: heavy and light. The light type is used in water supply and sanitation. Heavy type is used for fecal, drainage systems. According to the length of the cable are divided into two, five and ten meters. The disadvantage of the method is that it cannot be used in wells and pipelines. As well as a limitation in the diameter of the well, which is at least forty centimeters. For this reason, this type of protection is not universal.
4. Level switch consists of board electronic type with three electrodes. One controls, two work. The function of the sensors is to give a signal. The sensors are immersed in the well at different heights. The control sensor is installed above the level of the pump. When the liquid level drops, the signal from the sensor enters the level switch, 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 is working. The trip delay time is set by a special device-potentiometer, which is located on the front panel of the relay. When setting, you must take into account that the position on the left is the minimum delay, and on the right is the maximum. When the delay time expires, the machine turns off. The unit is switched 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 compatible with single phase pump higher power or with a three-phase pump, a magnetic type starter is used, suitable for power.