Most private houses have an autonomous water supply, which is provided by a pump. With various configurations 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 speed and the pump turns off.
1 What is dry (idle) running?
Each natural source of 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, there are accidents and planned outages.
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.
2 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.
2.1 Protection relay
A simple electromechanical element that responds to changes in pressure in the water supply system. When the pressure drops below a 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.
2.2 How to connect a dry-running relay to the pump (video)
2.3 Water flow control
The use of a pump with dry-running protection involves the inclusion in the system of devices that control water flow:
- relay (sensor);
- controller.
The former belong to the group of electromechanical devices, the latter are electronic.
2.4 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 an electromagnetic field by a turbine rotating in a flow of water. 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 entered into the system particulate matter(sand), interruptions in operation or their complete stop are possible, which requires partial dismantling of the water supply system.
2.5 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 responsive 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.
3 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.
3.1 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. turn off the pump both when the water level drops and when it excessive quantities in a limited space.
The principle of operation is as follows: the sensor is placed so that the float is on the surface of the water at 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 open phase wire, 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.
3.2 Electronic
Such devices perform the same functions as float devices, but their operating principle is different.
Two electrodes are lowered into the water of a source or storage tank. One to a depth to the minimum 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, control of 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.
Significantly reducing the service life of the pump is an emergency operating mode without water, the so-called “dry running”. Water performs both lubricating and cooling functions. Without fluid, the pump quickly overheats, parts become deformed, and the motor can burn out. Short-term dry running negatively affects equipment performance, regardless of the type of pump (drainage, submersible or surface pump).
To prevent breakdowns, automation is used:
- float switch;
- dry running sensor for pump;
- dry running relay.
Protection must be provided in a timely manner, since repair costs after a “dry run” are not included in the list warranty cases. Having disassembled the pump, a specialist will quickly determine the cause of the breakdown. The operating instructions indicate that operating the pump without water is prohibited.
Let's consider the main situations of insufficient water supply:
1. Wrong choice pump Happens more often in cases with wells if:
- the pump productivity exceeds the well flow rate;
- the dynamic level of the well is below the pump installation level.
2. Clogging of the pumping pipe (typical for surface models).
3. Violation of the tightness of the pipe through which water flows.
4. If there is low water pressure (or lack thereof) in the water supply system to which the pump is connected. Without automatic devices the pump itself will not turn off and will continue to “idle” until it is turned off or it breaks.
5. When supplying water from an excised source (container), it is necessary to constantly monitor the level of the incoming liquid.
Methods for protecting pumps from operating without water
Protection against “dry running” of the pump is provided by automation - sensors and relays that block the power supply at the moment the “waterless” mode appears or in advance. Triggering occurs differently in devices, and depends on the definition of the following quantities:
- water level;
- pressure in the outlet pipe;
- water flow;
- combined indicators.
Let's take a closer look individual species automatic protection.
Water level switch and float
The level switch and float sensor operate to monitor the water level. The level control relay regulates the operation of the water control valves and pump starters. It is one of the most reliable, but also expensive methods of protection. The main advantage is that it turns off the pump before it runs dry.
The relay includes an electronic board, sensors (three electrodes: two working, one control) and connecting single-core wires.
Operation scheme: control sensor is installed above the pump, working sensors are installed on different levels wells; When the water level drops to the control sensor, the pumping unit stops. When the water reaches the level of the control sensor again, the pump will automatically start working.
The main sensor board is located in a dry place, usually inside the house.
A float sensor (switch) can effectively solve the problem of “dry running” in wells and water supply from containers. It is mounted above the pumping unit. The trigger level is controlled by the length of the float cable and the specified location of the sensor.
The switch cable is connected to the phase supplying power to the pump. When the water level drops below the float sensor, the electrical circuit opens and the pump stops.
The fixed float level is selected taking into account the presence of water in the container at the moment the sensor is triggered. For submersible and surface pumps The “critical” water level should be located above the bottom valve or suction grille of the pump.
A float switch can be used to protect drainage and well pumps. For protection pumping units operated in a network pipeline or wells, it is necessary to use other automatic installations.
Relay and pressure sensor
To determine the pressure level at the outlet pipe, a pressure switch and a pressure sensor operate. The relay is installed minimally permissible norm pressure - usually 0.5 bar. You cannot adjust the maximum pressure level yourself. You can use a pressure switch as protection if the pump operates with a hydraulic accumulator.
When the pressure switch operates, the contacts open if the pressure drops to the set limit. It should be noted that the entire range of household pumping units can pump water at a pressure of 1 bar. Therefore, in practice, the pressure switch is activated when the water supply is completely stopped.
The relay does not warn of emergency danger, but simply detects the beginning of the “dry running” mode, turning off the pump. After the liquid supply is restored under appropriate pressure, it will be possible to turn on the pumping unit manually. Before each start, you must fill the pump with water yourself.
More wide range actions of pressure sensors. They signal that the pump stops working when the pressure drops to 1 bar or below. Pressure sensors have found their application in domestic pumping installations of network pipelines, fire extinguishing and water supply pumping stations.
When the pressure of the water flow at the pump inlet decreases, sensors are triggered and send a signal to the control panel of the pumping unit.
Water flow sensor
The operating principle of the flow sensor is based on measuring the flow of water passing through the pump. The sensor consists of a valve (“petal”) located in the flow part and a reed switch microswitch. The petal is spring loaded and has a built-in magnet on one side.
Scheme of operation of the sensor: under the influence of water pressure, the petal valve moves - the spring begins to compress, and the magnet interacts with the reed switch relay. Closing the contacts causes the pump to operate. Without any liquid entering, the valve spring expands, moving the magnet to its original position - opening the relay contacts turns off the pumping unit.
The flow sensor is built into booster pumps with low capacity. Works to determine two values (pressure level and flow) of the flow switch, with additional function pressure switch, so-called “press control”. The device is distinguished by its compact dimensions ( light weight and volume).
At a pressure level in the range of 1.5-2.5 bar (depending on the automation model), the pump receives a command to start working. The pump performs its functions until the water supply stops. Due to the flow sensor built into the relay, the pump stops working. The sensor very quickly registers the appearance of a “dry running”, which allows you to avoid a long stay in the “waterless” operating mode.
Mini AKN
A universal device from emergency modes is a Mini AKN. It is based on electronic protection of single-phase pumping units. The mini AKN reacts to the power factor and current of the pump motor. The main advantages of the device: comprehensive protection from emergency situations, small dimensions and energy consumption, ease of installation, reliability.
Situations when protection may not be used
You can do without installing a pump dry running sensor only in certain cases:
- constantly monitoring the water supply from a well or borehole (you will have to be nearby to respond in time to changes in water flow);
- pumping is carried out from an inexhaustible source;
- the drilled well has a high flow rate;
- the person controlling the operation of the pump has operational experience and knows the principle of operation and design of the pump.
If the operation of the pump becomes intermittent, or it shuts down completely, it cannot be restarted without identifying and eliminating the causes of the breakdown.
Pumping equipment operates correctly only when the flow of liquid through it is constant. If the fluid supply stops, dry running occurs, and, as a result, the pump breaks down.
To prevent the pump from running dry, special devices are installed on the water supply system.
1 Dry running relay: purpose and design
There are several types of devices that will turn off equipment without water supply:
- dry running relay for pump;
- liquid flow control sensor;
- water level sensor.
Each of these devices has different area application and operating principle.
The dry running protection relay is a simple electromechanical device, which controls the presence of pressure in the water supply: if the pressure drops below the permissible level, electrical circuit will open and the pump will turn off.
The relay device contains a sensitive membrane that responds to pressure and a contact group that is open in the normal state. As soon as the pressure drops, the membrane presses on the contacts, they close, and the power supply is turned off.
A drop in pressure is possible when the water supply in the pipeline stops, the filter becomes clogged with debris, or the suction pipe is above the liquid level. In each of these cases, a “dry running” of the pump occurs, which must be stopped, which is what the protective element does.
The operating pressure of the medium to which the dry-running relay reacts is set by the manufacturer and ranges from 0.1 atmospheres to 0.6 atmospheres. The idle relay is installed on the surface, but there are also models for internal placement in a sealed housing.
1.1 Installation
The device operates normally in any pipeline design that does not include a hydraulic accumulator. It can also be installed in conjunction with a hydraulic accumulator, but such a scheme will not provide complete protection against dry running of the pump.
The reason is the peculiarity of the structure and operating principle: the protective element is installed in front of the fluid pressure switch and the hydraulic accumulator, and a check valve is mounted between the pumping unit and the protective device.
At the same time the membrane of the device is constantly under pressure, which creates a hydraulic accumulator. This standard scheme, but sometimes situations arise when a running pump does not turn off when the water flow stops and fails.
For example, a dry running situation has arisen: the pump is turned on, the container or well is almost empty, but there is a small amount of liquid in the battery. Since the lower pressure threshold is set to work at 1.4-1.6 atmospheres, it is there, but the membrane will be pressed out, and the pump will continue to idle.
It will stop working when most of the water from the accumulator is pumped out or when the engine burns out. This means that the pressure in the pipeline has dropped to a critically low level and the protective relay has tripped. Based on this, in systems with hydraulic accumulators it is advisable to install other devices to protect against dry running of the pump.
It is most effective to connect a dry-running relay paired with a surface pumping unit, when the check valve is installed after the pumping equipment.
2 Float switch
A float switch is the simplest and most cheap way protect circulation pump from overheating and breakdown when running dry. The advantage of the device is that it can be used as a working medium level sensor and as an actuator.
They install switches in tanks, wells, tanks and use them in controlling household and industrial pumps in water supply and sewer lines. The required level of switch operation is determined by the length of the cable.
Several float switches can be placed in one container, each of which will perform a separate function. function for managing main or backup pump equipment.
Dry-running float sensors come in light and heavy sizes. The former are used for supplying and draining water, the latter - in sewers and drainage pipelines.
For correct operation of the device, a minimum well diameter of 40 cm is required. This feature does not allow float switches universal remedy protecting the pump from running dry.
2.1 Safety pressure switch
The device is a conventional pressure switch, equipped with additional protection against idling when the pressure drops below factory settings.
This pressure switch controls the switching on and off of the surface or well pump, if the pipeline diagram includes a hydraulic accumulator or a connection to an automatic pumping station is provided. The relay operates at 0.4-0.6 atmospheres. This parameter is set at the factory and cannot be changed.
If pressure fluctuations inside the pipeline are within specified limits, then the pressure switch does not operate and the pump operates normally. When the pressure drops to the set values, which happens in the absence of water, the dry running sensor is activated, the contacts supplying the circuit are opened, and the device for pressure movement of liquid is turned off.
The process of starting the pump is carried out only manually by pressing the lever. Before this, the cause of the engine stopping is determined and eliminated. Required condition during startup – filling the pump with water.
2.2 Which protective device should I choose?
2.3 Description of connecting the pumping station (video)
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.
Not allowed for use hydraulic equipment with faulty dry-running protection sensors.
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 installation must be disconnected from the power supply, and you must also wait a few minutes for the capacitors to completely discharge. Water must be removed from the accumulator cavity. We also dismantle 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;
- record the readings on the pressure gauge, repeat the operation several times and display the most optimal values pressure empirically.
During adjustment work you will need to take into account the physical capabilities of the pump. Given the rated 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 breakdowns of this equipment with normal energy supply. Popular material For the manufacture of pumps, thermoplastic is used, which can withstand long-term operation and has an affordable cost.
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:
- Float switch
The element relates to budget decisions. It is used to pump water from accessible containers. It only protects against overflow.
- 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.
- Flow switch with functions
If there is no water pumping through the relay, automatic shutdown power supply 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
Dry running of a pump is the operation of the unit in the absence of the required amount of pumped liquid. If water or other liquid runs out, the pump is protected from dry running. It can be presented in the form of several different devices, the most common of which is considered to be a dry-running relay for the pump.
Dry running sensor for pump - operating principle and design
There are several most common devices, the main task of which is to protect pumps from running dry. These include:
- Dry running protection relay;
- Sensor for monitoring the volume of pumped liquid;
- Water quantity sensor - float.
Each of the listed devices is used in various pumps with different tasks and functions. The most commonly used in pump production is the dry-running protection relay. It has a fairly simple design, but shows high efficiency when operating centrifugal, vortex and other types of equipment.
A relay is a simple electromechanical device designed to control the pressure inside a pipeline. As soon as the pressure drops below the minimum permissible limits, the electrical circuit will instantly open and the unit will turn off.
The relay device includes a sensitive membrane that responds to pressure fluctuations and a group of contacts, which in the normal state is in the open position. As the pressure rises, the membrane begins to put pressure on the contacts, which leads to them closing and stopping the supply of electricity to the pump motor.
Each dry running sensor for a pump is designed to operate in an environment with a specific pressure. Depending on the manufacturer’s settings, the equipment can operate within the range of 0.1 to 0.6 atmospheres. As a rule, the relay is installed on a surface outside the pump housing, but 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 its design. On the other hand, you can install the relay in conjunction with a hydraulic accumulator, however, such installation will not provide complete protection against dry running.
The reason for this lies in the operating principle and structural features of the sensor: the protective relay should be mounted in front of the hydraulic accumulator and the fluid pressure switch. In this case, a dry running valve is installed between the protective device and the pumping unit.
In this case, the relay membrane will be exposed to constant pressure created by the hydraulic accumulator. This is a fairly typical scheme, but in most cases it will not help protect the pump. For example, consider the following case: when the pump is turned on and pumps out liquid from an almost empty container, the remaining liquid remains in the hydraulic accumulator. Since the lower pressure threshold is set by the manufacturer at 0.1 atmospheres, there is actually pressure, but the pump will run idle.
As a result of this, the pump motor will stop working only in cases where the hydraulic accumulator becomes completely empty, or when the motor 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
Connecting the relay can be done by anyone who has the slightest understanding of how it works electrical appliances. First of all, you will need to remove the protective cover of the device. Under it there are 4 contacts - two for input and two for 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 power of the unit. The outlet must be grounded.
Configuring the connected protective relay
Dry running relay for pumping station or household pump you need to not only connect, but also configure it correctly. This should be understood as adjusting the dependence and rigidity between the switched contacts and the platform, which is susceptible to operating pressure. These characteristics can be adjusted by changing the spring stiffness, which must be weakened or compressed by turning the nuts. Below, as an example, the location of these nuts in the RDM-5 relay is presented. Most other modern protective devices They have a similar design, and the adjusting nuts on them are located in the same way.
According to the factory settings, the minimum pressure for the relay to operate is 1.4 atm. The maximum pressure, in this case, is 2.8 atmospheres. If you need to change the minimum pressure threshold, then to do this, nut “2” must be tightened clockwise. At the same time, the upper pressure threshold will also increase. The difference between them will always be 1.4 atmospheres.
If you need to adjust the difference between the lower and upper threshold pressure, then to do this you need to twist the nut “1”. When you rotate it clockwise, this value will increase, and counterclockwise, it will decrease.
Protective relays LP 3 - description and characteristics
A device of this hydrostop type is used in water supply systems and is intended to shut off borehole and surface pumps in automatic mode. Devices are switched off immediately after the liquid level drops below permissible limits. To the main technical specifications relay refers to:
- The maximum switching current level is 16 A;
- Temperature range of pumped water – from 1 to 40 °C;
- Pressure range during operation – from 0.5 to 2.8 atmospheres;
- Electrical protection class IP44.
The manufacturer provides a 1-year warranty for this type of relay model. The device shows reliability and effective protection pumps during operation.