For continuous and trouble-free operation of the pump (pumping station), a prerequisite for operation is the presence of a sufficient amount of water. Regardless of where the intake comes from (well, well, open reservoir, centralized or drainage systems), pumping equipment must be equipped with protection against idle move. This is due to the fact that water, when passing through the pump, provides its lubrication and cooling. In the absence of water or its insufficient quantity, the operating pump overheats and fails.
In order to exclude damage that is not covered by the manufacturer's warranty obligations, a pump dry-running protection relay should be installed.
1 Causes of dry running
It is necessary to connect a dry-running relay to protect pumping equipment in the following cases:
- when the performance (power) of the borehole pump significantly exceeds the resource capabilities of self-recovery of a sufficient volume of water in the well;
- the natural water level in the source is significantly lower than the installation level of the pump;
- there is constant clogging with sand, silt, foreign objects of the intake pipe or filter mesh;
- the tightness of pipes and their connections is violated from the physical influences of the soil or due to improper installation;
- the circulation pump operates at low water pressure or insufficient water in heating (cooling) systems;
- water is taken from a source being filled - a well (well) slowly restoring the water level, a storage tank, an unstable water supply system.
Connecting the idle relay to the pumping station is a prerequisite, since it operates in automatic mode without third-party control.
2 Dry running protection devices
The main devices that exclude the possibility of pumping equipment without water in automatic mode include:
- dry running sensor for the pump;
- dry running relay for the pump;
- pressure switch;
- float switch.
Under certain conditions, sensors and relays interrupt the power supply to the pump motor, causing it to stop. The protection operation is determined by the following parameters:
- water level;
- outlet pressure;
- by the strength of the water flow.
The combined control on several parameters at the same time is possible.
2.1 Float switch
Float-type dry-running sensors work effectively when installed in wells, drainage systems and storage tanks. The actuation process (power off) occurs when the water level in the source drops to a minimum value. When, together with the decreasing water, the float drops to the lower operating level, the contacts open in the power supply phase of the pump, which leads to its stop.
The float switch can be connected to submersible or surface pumps. In this case, its location should be above the bottom valve or the protective grille of the suction pipe with fixation of operation by insufficient water level.
Installation of such a sensor is not possible when taking water from wells and centralized water supply systems.
2.2 Level switch
With the help of this device, the water level in the source (tank) is monitored. When the level drops to a critical value, the control relay is activated to adjust the operation of the flow valves or turn off the pump.
The main advantage of this protection is that the power supply to the pump is switched off before it starts running in idle mode.
The level switch consists of an electronic board and three electrodes (sensors) that are mounted on different height in close proximity to each other. The electrodes, being immersed, exchange low-frequency currents, since water is a good conductor of electricity. When the water level drops to the lowest control sensor, the electrical connection between the electrodes is interrupted, which leads to the operation of the relay to stop the pumping device. When the working water level is restored, the pump is switched on again.
2.3 Pressure switch
The principle of operation of the pressure switch is based on determining sufficient pressure (from 1 bar) at the outlet pipe of the device pumping water. In the event of a pressure drop below 0.5 bar, the contacts are opened by the pressure switch.
When the pressure is restored, with sufficient for safe work pressure pump, you must manually fill the dry pump with water and turn it on yourself.
Pressure switches are used when installing household pumps connected to centralized water supply networks, water supply and fire extinguishing stations. Installation is recommended at pumping stations that work with a hydraulic accumulator (storage tank).
2.4 Flow sensor
The device is a petal valve, which is installed in the flow part of the pump. The principle of its operation is to respond to the force of the flow (the passage of a certain volume of water in the pipe per unit of time).
The spring-loaded petal of the sensor, under the action of passing water, compresses the spring and interacts with the reed relay through the magnet fixed to it. In this case, the contacts included in the power supply circuit of the pump are connected. In the presence of a strong flow, the petal sensor is constantly deflected and the pump motor is running.
Without liquid in the pipeline or its weak movement, the spring deflects the petal with the magnet to its original position, which leads to the opening of the contacts and the stop of the pumping device.
The flow sensor has compact dimensions and low weight, which allows it to be used not only in industrial, but also in household devices.
3 Is it possible to do without protection against dry running?
In some cases, this is acceptable provided that:
- the pump does not work often and for a short time (seasonal water supply in the country);
- constant control (observation) of the operation of the pumping device is carried out;
- water is taken from a guaranteed inexhaustible source;
- the user has sufficient operating experience, is familiar with the design and technical specifications water supply device.
3.1 How to connect a dry-running relay to the pump? (video)
Pump protection methods
In the "General" section, we will consider ways to protect pumps from "dry running". "Dry running" is the operation of the pump without fluid flow, most common cause failure centrifugal pumps. The problem, the operation of the pump without a fluid flow, is relevant to any type of centrifugal pumps: surface, circulation, borehole, fecal or drainage. During the operation of pumping equipment, the pumped liquid performs the functions of "lubricating" the working surfaces of the pump and cooling them. In the absence of flow, even if the pump is filled with water, due to friction at speed induction motor components 2850 - 2900 min -1 there is a rapid heating and boiling of the liquid. The working elements of the pump (diffusers, wheels) begin to heat up and deform. This primarily applies to pumps in which the working elements are made of heat-resistant plastic - noryl. The first indication that a pump has run dry is a reduction in its head and flow performance. More severe consequences lead to jamming of the pump shaft and overheating of the stator windings (the motor burned out). Manufacturers of pumping equipment in the installation and operating instructions indicate the unacceptable mode of using pumps without fluid flow. Which of the ways to protect pumping equipment from operation in the "dry running" mode to choose, the buyer determines independently. To facilitate its selection, consider the most commonly used and used methods. And so, these include the following protection methods: a float switch, a pressure switch with a dry-running protection function, a pressure switch and a dry-running protection switch, a flow switch, a level switch. Short review ways to protect centrifugal pumps.
float switch
Protecting pumping equipment from "dry running" with the help is one of the cheapest and most commonly used methods. The main advantage of this method of protecting and controlling pumps is that float switches can be used both as a water level sensor and as an actuator at the same time. They are mounted in storage tanks, reservoirs, tanks, pits, wells and are used to control household and industrial pumps in water supply, sewerage and sanitation systems. The required level of operation of the float switch is set by the length of the cable and the location of its installation. By changing the length of the arm, you can change the level of filling or emptying the tank. Several float switches can be installed in one container, and they can perform various functions, control the main or backup pump, control an automatic pumping station, or be used as a level or overflow sensor. Some types of well, drainage and fecal pumps available with built-in float switches. The pumps also have the ability to change the length of the float and thereby adjust the level of switching on and off the pump. Float switches come in two types, light and heavy. The light ones are mainly used in water supply and sanitation systems, and the heavy ones are used for drainage, fecal (sewer) effluents. Float switches are available with various cable lengths of 2 - 5 - 10 meters depending on the model. The maximum switching current for reactive loads (pumps, fans, compressors, etc.) is 8A: For normal operation of the float switch, it is necessary that the minimum diameter of the well be at least 40 cm. For this reason, floats cannot be used as a universal means of protection pumps from "dry running".
Pressure switch with dry run protection
This is a conventional pressure switch with additional function protection against the "dry running" mode when the pressure drops below the level set by the manufacturer. A pressure switch with dry-running protection controls the switching on and off of surface, borehole or well pumps based on pressure setpoints when they are used in conjunction with or the operation of an automatic pumping station. The shutdown pressure of the relay in the "dry run" mode is usually 0.4 - 0.6 bar, this is the factory setting and cannot be changed. If the pressure in the water supply system changes within the settings set on the pressure switch, the pump works without failure. When the pressure at the outlet of the pump drops to a level of 0.4 - 0.6 bar, and this can happen when the pump starts to work in the absence of water. At this pressure, the relay is switched off on a "dry run". To restart it, you must first eliminate the cause of the pump shutdown in the "dry run" mode. Then fill the pump with the pumped liquid. After forcibly press the lever and turn on the pump.
Pressure switch RM - 5, RM - 12 and dry run relay LP3
Pressure switch and dry run switch
Another is the joint useWith . The pressure switch controls, according to the set pressure values, the on and off of the surface, borehole or well pumps when they are used in conjunction with hydraulic accumulators or the operation of an automatic pumping station. Adjustable with pressure switch autonomous system home water supply or irrigation system for specific tasks. And the "dry running" relay LP 3 in this case is used to protect the pump or automatic pumping station from working in the "dry running" mode. The "dry run" mode is controlled according to the pre-set pressure values on the relay. Relay LP3 turns off the pump when the pressure in the system becomes lower than the preset value. To start the device into operation, it is necessary to press and hold down the red button until the pressure in the water supply system rises higher than that set on the relay. Relay LP3 can also be used to protect pumping equipment from "dry running", when connected directly to the network pipeline. The dry-running switch is activated when the pressure in the water supply system becomes higher than the preset value. When using a dry-running relay to control pumping equipment, the maximum switching current is 10A.
Pressure switch RM - 5, RM - 12 andrelay "dry running" Spin
Next way to protect pumps from "dry running"- this is the combined use of the pressure switch RM-5 and RM-12 with. Turning on and off surface, borehole, well pumps when they are used in conjunction with hydraulic accumulators, as well as automatic pumping stations occurs according to the given pressure values. pre-set on the relay, When the maximum set pressure value in the water supply system is reached, the relay turns off, and when the pressure drops to the minimum set value, the relay turns on. With the help of a pressure switch, an autonomous water supply system at home or an irrigation system is configured for specific tasks. Spin is used to protect pumping equipment from running without fluid flow or, more simply, from “dry running”. The device turns off the pumping equipment when the water in the tank, well or well runs out, as well as after all taps are closed. When energized, the Spin relay starts the pump and keeps it running. When the water flow stops completely, the device starts a timer, which provides a delay in turning off the pump for a certain period of time, pre-set when setting up the device. After this time, the pump switches off. In the process of putting the equipment into operation, it is necessary to set the delay time for turning off the relay due to the lack of liquid flow. The shutdown delay time depends on the volume of the accumulator and the type of pump used. The pump is put into operation when the check valve with a magnet inside the device moves under the action of the water flow (when the water tap is opened), the magnet closes the contacts of the reed switch and the automation gives a command to turn on the pump. Electrical connection must be carried out in the following sequence: Socket → Pressure switch → Spin → Pump. The Spin relay has an auto-restart feature (multiple attempts) that turns on the pump at regular intervals after it goes dry due to lack of fluid flow. After the implementation of these attempts, the device finally goes into an accident. To put it into working mode, you must press the restart button. The maximum switching current is 12A.
Pressure and flow regulators
Unlike a pressure switch in its various combinations, where it is necessary to install a hydraulic accumulator together with pumping equipment, if you use pressure and flow regulators, a hydraulic accumulator is not needed. When turned on, the regulator starts the pumping equipment and maintains this state as long as there is water consumption. When water consumption stops completely, the pumping equipment is turned off due to the lack of liquid flow with a time delay. In the control circuit of pressure and flow regulators there is: a magnetic relay (reed switch). Either a spring-loaded check valve or a float with permanent magnet, The flow of water displaces the check valve with a magnet, and the contacts of the reed switch close under the action of the magnet, thereby the electronics determines that the pump is pumping water to consumers. As soon as, for some reason, the pump stops supplying water, under the action of a spring, the check valve returns to its original state, and the float goes down, the reed switch contacts open, and after a delay time, the pump turns off. The time delay is necessary to reduce the number of switching on / off of the pump, if the water flow is very low. In pressure and flow regulators there is no limit on the upper limit of the shutdown pressure. The pressure in the system is equal to the maximum head of the pump, and shutdown occurs only in the absence of flow. When the pressure in the water supply system drops to a value of 1.5 bar (in Brio and Flusstronic series 3 it is possible to change the lower switch-on value), the pumping equipment is switched on. The main advantage of the relay is its small dimensions and weight. In case of a temporary power outage, the devices start the pumping equipment automatically after it is supplied. Due to the presence of a buffer tank, the possibility of hydraulic shocks is excluded when the pump is turned on and off.
Dry running relay with level sensors
Dry running relay
The "dry running" relay allows you to control the level of liquid in the well and controls the power supply of the downhole pump to prevent its operation without liquid. The control of the required liquid level is carried out by an electric microcurrent circuit "level sensor - pump housing". On the front panel of the relay there are control and indication elements:
- LED "NETWORK" - signals the presence of supply voltage to the relay;
– LED "LEVEL" - indicates the presence of water in the controlled pipeline (reservoir, well capacity);
– potentiometer for changing the value of the delay for switching off the relay in the absence of water (0.5 ... 12 sec.).
The principle of operation of the relay is as follows. When installing the pump in a well or in a tank, a level sensor is additionally mounted, which is connected to the relay using a single-core cable with a cross section of not more than 2.5 mm 2. The signal cable is attached to the cable or pipeline going to the pump. The pump housing is used as the second electrode. If the level sensor is submerged, then a microcurrent flows between it and the pump housing. In this case, the pump operation control contacts are closed, and the pump pumps water. In the case when the level sensor comes out of the water (the pump has pumped out the water), the microcurrent circuit breaks and the timer starts to count down the delay time specified during the settings. The shutdown delay time is set using the potentiometer displayed on the front panel of the dry-running relay. In the extreme left position - the delay will be minimal, in the extreme right - maximum. After this time, the contacts of the relay controlling the operation of the pump are switched off. The pump is switched on when the level sensor is back in the water. The dry-running relay can be used with low power single-phase borehole pumps (up to 1.5 kW, 11 A). If it is necessary to connect a more powerful single-phase pump, or a three-phase pump, it is necessary to use a magnetic starter or a contactor of the appropriate power.
There are a huge number of varieties of "dry running" relays with level sensors. We have considered the simplest option when using one level sensor and a pump housing. There are schemes with two and three level sensors. The principle of their work is similar to the option discussed above.
This is not a complete list of devices for protecting pumping equipment from the "dry run" mode, and we did not set ourselves the task of considering all existing methods and methods of protection of centrifugal pumps.
Thank you.
Significantly reduces the life of the pump, emergency operation without water, the so-called "dry running". Water performs both lubricating and cooling functions. Without fluid, the pump quickly overheats, deformation of parts occurs, and the engine may burn out. A short dry run adversely affects the performance of the equipment, regardless of the type of pump (drainage, submersible or surface).
To prevent breakage, automation is used:
- float switch;
- dry running sensor for the pump;
- dry run relay.
Protection must be provided in a timely manner, since the cost of repairs after a "dry run" is not included in the list of warranty cases. Having disassembled the pump, the specialist will quickly determine the cause of the breakdown. The operating instructions indicate that the operation of the pump without water is prohibited.
Consider the main situations of insufficient water supply:
1. Incorrect choice pump. More often occurs in cases with wells if:
- pump performance exceeds well flow rate;
- the dynamic level of the well is below the level of the pump installation.
2. Clogging of the pumping pipe (typical for surface models).
3. Violation of the tightness of the pipe through which water enters.
4. With low water pressure (or lack thereof) in the water supply to which the pump is connected. Without automatic devices the pump itself will not turn off and will continue to "idle" work until it is turned off, or it breaks down.
5. When water is supplied from a source (tank) to be cut off, it is necessary to constantly monitor the level of the incoming liquid.
Ways to protect pumps from running without water
Protection against "dry running" of the pump is provided by automation - sensors and relays that block the power supply at the time of the appearance of a "waterless" mode or in advance. The operation occurs in different devices, and depends on the definition of the following quantities:
- water level;
- pressure in the outlet pipe;
- water flow;
- combined scores.
Let's consider in more detail certain types automatic protection.
Water level switch and float
Tracking the water level, the level switch and the float sensor work. The level control switch regulates the operation of the water control valves and pump starters. It is one of the most reliable, but also expensive ways of protection. The main advantage is that it turns off the pump before a “dry run” appears.
The relay includes an electronic board, sensors (three electrodes: two working, one control) and single-core connecting wires.
Scheme of work: control sensor is installed above the pump, working sensors - at different levels of the well; 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 turn on.
The main sensor board is located in a dry place, usually in the house.
The float sensor (switch) is able to effectively solve the problem of "dry running" in wells and water supply from containers. It is mounted above the pumping unit. The level of operation is regulated 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 switch, the switch opens. electrical circuit– the pump stops.
The fixed float level is selected taking into account the presence of water in the tank at the time the sensor is triggered. For submersible and surface pumps, the “critical” water level must be above the bottom valve or suction grate of the pump.
You can use a float sensor to protect drainage and well pumps. For guard pumping units operated in a network pipeline or wells, other automatic installations must be used.
Relay and pressure sensor
To determine the pressure level at the outlet pipe, a pressure switch and a pressure sensor function. The minimum allowable pressure is set in the relay - usually 0.5 bar. You cannot adjust the pressure limit yourself. It is possible to use a pressure switch as protection if the pump operates with a hydraulic accumulator.
When the pressure switch is operating, the contacts open if the pressure has dropped to the set limit. It should be noted that the entire range of domestic 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 an emergency, but simply states the beginning of the "dry run" mode, turning off the pump. After the resumption of the fluid supply under the appropriate pressure, it will be possible to turn on the pumping unit manually. Before each start, you must fill the pump with water yourself.
Wider range of action for pressure sensors. They signal the cessation of the pump when the pressure drops to 1 bar and below. Pressure sensors have found their application in household pumping installations of network pipelines, fire fighting and water supply pumping stations.
When the pressure of the water flow at the inlet to the pump decreases, sensors are triggered that send a signal to the control panel of the pumping unit.
Water flow sensor
On measuring the flow of water passing through the pump, the principle of operation of the flow sensor is built. The sensor consists of a valve ("petal") located in the flow part and a reed 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. Closing the contacts causes the pump to work. Without the flow of liquid, the valve spring is unclenched, moving the magnet to its original position - opening the relay contacts leads to the shutdown of the pumping unit.
The flow sensor is built into booster pumps with a small capacity. Works to determine two values (pressure level and flow) of the flow switch, with an additional function of the pressure switch, the 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), a command is sent to the pump to start working. The pump performs its functions until the withdrawal of water is stopped. Due to the flow sensor built into the relay, the pump stops working. The sensor very quickly registers the appearance of a "dry run", which avoids a long stay in the working "waterless" mode.
Mini AKN
The universal device from emergency modes is Mini AKN. It is based on electronic security single-phase pumping units. The mini ACV responds to the power factor and current of the pump motor. The main advantages of the device: comprehensive protection against emergencies, small size and power consumption, easy installation, reliability.
Situations when you can not use protection
It is possible to do without installing a pump dry running sensor only in some cases:
- constantly monitoring the water supply from a well or well (you will have to be nearby in order to respond in time to a change 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 experience in operation, knows the principle of operation and design of the pump.
If the operation of the pump has become intermittent, or it has turned off altogether, it must not be restarted without identifying and eliminating the causes of the breakdown.
Dry running switch - a device that monitors the level of liquid in the source, and when it falls, turns off the well pump to protect it from overheating as a result of idling. Any pumping equipment that pumps water becomes unusable in the absence of a working medium. Therefore, the presence of its sufficient level and pressure is monitored by a water flow sensor for the pump. "Plumber Portal" will talk about the features of choosing this device.
Dry running of a pump is the most common cause of pump failure. In addition, in this case, the equipment is not eligible for repair under warranty, as the owner allowed the device to be used incorrectly.
The pump starts to work in "idle" mode most often for the following reasons:
- Incorrect selection of the height of the suspension of the water pump in the well or well shaft. Often this happens when the depth of the source has not been calculated in advance. When the equipment pumps out the liquid medium to the level of its location, it begins to suck in air, due to which the electric motor of the device overheats.
- In the source, for natural reasons, the volume of water has decreased. For example, the bottom of the well silted up or the liquid did not have time to accumulate in the well after a recent pumping out. Therefore, after pumping out the water, you need to wait a certain period for the source to fill up again.
- If a surface pump is used, placed on the water surface, then the reason for its malfunction is often that the suction pipe loses its tightness, and water is captured along with air, as a result, the engine of the device is not cooled enough.
So, the pump is not equipped with protection in the form of a sensor and a dry-running relay, then the pump quickly overheats and the electric motor, as well as other parts of the structure, burn out. The plastic elements of the pumping unit, in the absence of sufficient lubrication and cooling, are deformed, which will first lead to a reduction in the performance of the device, and then initiate its overheating, self-jamming of the shaft and engine breakdown.
Varieties of dry running sensors
Expensive modifications of pumping units are already equipped with built-in dry-running protection sensors. For example, all pumps of the Grundfos brand, as well as some models from the manufacturer Sterwin, Watt, Whirlwind and Wilo are also equipped with such devices.
When operating budget devices, sensors must be independently connected to submersible pump. Let's take a closer look at various types these devices and how they work.
- protection relay;
- level sensors;
- water flow and pressure sensors.
Protection relay
It is an electromechanical device that controls the pressure of water flowing through pump unit. When the pressure drops, the power circuit opens.
The pump protection relay against dry running consists of a membrane, a contact group and several wires. The membrane controls the fluid pressure. In working condition, it is open. When the pressure drops to 0.1-0.6 atmospheres, the membrane compresses the relay contacts and the pump turns off. Lowering the pressure to this value indicates the occurrence of the following violations:
- the liquid pressure has dropped to a minimum level due to the depletion of the source;
- clogging of the pump filter;
- the pump is above the water level, so the pressure has dropped to zero.
The protection relay can be built into the device case or mounted on the surface as a separate part.
If the design of the water supply contains a hydraulic accumulator, then the protective mechanism is installed together with a pressure switch, in front of the accumulator.
Water level sensors
This type of equipment is used to establish the actual level of liquid in a well or well. Two types of sensors can be used:
- Float switch. The connection diagram of the dry run analyzer must be assembled in such a way that its contacts are included in the power supply circuit of the pump motor. The float is afloat. When the level of the working medium decreases, the float changes its position, its contacts open, the pump turns off. This is the easiest way to protect, which is durable and easy to operate.
Advice! In order for the float to work in a timely manner, you need to successfully configure it. It is important that the pump housing is still immersed in the liquid medium when the sensor is triggered.
- Water level sensor. This is a relay that consists of two separate devices lowered on different level depths. One fixture is dipped to the lowest possible level of pump operation. The second sensor is located slightly lower. When both devices are located directly under water, a small current flows between them. If the level of the working medium decreases to the minimum value, then the current stops flowing, the sensor is triggered, opening the power circuit.
- Sensors that control the level of the liquid make it possible to turn off the pumping equipment before the body of the device is above the surface of the water surface. This means that the equipment is thoroughly protected from damage.
Water flow and pressure sensors
There are two types of pump water flow sensors that monitor the flow of fluid through the pump and protect it from running dry. These are flow switches and flow controllers.
- The flow switch is an electromechanical type product. There are turbine and petal. The principle of their operation is also different:
- in the rotor of turbine relays there is an electromagnet that generates an electromagnetic field when fluid passes through the turbine. Specialized sensors read the electrical impulses that are generated by the turbine. When the pulses disappear, the sensor turns off the pumping device from the power supply;
- there is a flexible plate in the petal fixtures. If water does not enter the pump, the plate moves away from its original location, as a result of which the mechanical contacts of the relay open. In this case, the power supply to the pumping device is interrupted. This option is characterized by simplicity of design and affordable price.
These block modules turn off the pump if there is no water flow and turn on the device if the pressure in the system falls below a predetermined level.
- Flow controllers (automation unit, press control). These are electronic products that monitor several important flow characteristics simultaneously. They check the pressure, signal the cessation of water suction, automatically turn on and off the pumping equipment. Many mechanisms are equipped check valves. High reliability justifies the high cost.
Which security device should you choose?
It is difficult to select the required model of a dry-running protective sensor, since several important factors must be taken into account at once:
- depth of the water source;
- well diameter;
- features of the pump used. For example, a submersible or surface model is used;
- consumer financial capacity.
For example, the simplest and cheapest device to protect the pump from dry running is a float sensor. But it should be borne in mind that its use in a well of small diameter is impossible. But for the well, it fits perfectly.
If the water in the working tank is obviously clean, then the most the best option will use a water level sensor. If you are not sure about the quality of the water supplied to the pump, it is better to use a flow switch or a water pressure sensor.
If there is a possibility of clogging the pump filter with debris or dirt, then it is not advisable to use a level sensor. He will show normal level water, although no water will be supplied to the pump unit. The result will be a burnout of the pump motor.
In this way , it is possible to use a pump without a dry-running relay only if it is possible to constantly monitor the flow of water from a well or well. Then the user can quickly turn off the pumping station if the liquid stops flowing into it. Otherwise, it is better to install a protective sensor in advance. Its cost pays for itself, given the price of a new pump to replace burned-out equipment.
Recently, many questions have arisen about the causes and consequences of the so-called dry running of pumps. Moreover, there was a clear lack of understanding of the very process of the occurrence of a dry run.
Looking at the top of "Yandex" for the query "dry running of the pump", I was surprised to find that 9 out of 10 proposed definitions, to put it mildly, are not entirely correct. And if you call a spade a spade, then it is not true at all. Namely, in the definition: “dry running is the operation of a pump without water,” at least one very important word is missing. But first things first.
Are pumps dry running?
I don’t know if it will be a discovery for you, but in fact the “dry running of the pump” is a “disease” of exclusively domestic pumps. No industrial pump is "afraid" of running dry. At all. Why? Interest Ask.
Because no industrial pump is designed to operate with a working environment exclusively below 50-60 degrees Celsius. It is simply not profitable for manufacturers to save on the quality of materials, risking losing expensive equipment at any time, only due to an increase in the temperature of the water in the pump.
What is the water temperature here? And you read the instructions for any household pump. Almost everywhere it is indicated that the permissible temperature of the pumped water should not exceed 60, 40, 37, 35 degrees. Because the materials from which some parts of the pumps are made begin to deform when the water temperature rises to 50-60 degrees. Manufacturers, as usual, are a little reinsured, indicating lower temperatures in the tolerances.
But the increase in the temperature of the water in the pump is a direct consequence of the dry running of the pump, when a whipped cocktail of air and water can heat up to decent temperatures due to friction against the walls of the pump casing and the impeller.
It turns out that if there were better materials from which pump parts are made, then such a problem as dry running would simply not exist. That's just how much these pumps would weigh, and how much they would cost - this is another question.
Is it so dry - this "dry run"
Let's go back to the definition I pulled from the Internet: "The dry running of the pump is the operation of the pump without water."
Above, we talked about the fact that pump parts are not afraid of the dryest run, but high temperature caused by it. However, from the school physics course, we know that air is an excellent heat insulator, and it is very, very problematic to heat a pan with air by sliding it on a cold metal plate. Yes, in principle, even if it is on a hot stove, the pan will heat up, but not the air in it.
How, then, can the parts inside the pump heat up from the rotation of the impeller, which does not come into contact with them, if “the pump runs without water”? Since there is an exceptionally excellent heat insulator - air, which cannot heat the internal parts.
Another thing is if, together with air, there is water in the pump, which perfectly accumulates and transfers the heat energy that occurs when the pump parts rub against the same water droplets in an airborne suspension whipped up by an idle threshing impeller.
So, it’s not so dry - this “dry run”. At least, completely without water - it is not terrible for the pump. But I don’t advise you to experiment, you can burn the gland, which is cooled just by water.
What is a "dry run"?
So what is this process that takes place in the pump and leads to catastrophic consequences for the pump itself? The time has come to say exactly that word, which, in my opinion, is sorely lacking in the definition of a dry run.
So:
Dry running is the operation of the pump without duct water or with a small flow that does not provide cooling of the pump parts.
It is this definition, it seems to me, that will be correct and reflect the essence of what is happening in the pump.
Thus, even if there is water in the pump, even if the pump creates pressure, even if you use water, if the pump or system characteristics are not properly selected, you risk burning the pump dry due to overheating of internal parts. By the way, such cases are described in the comments.
Therefore, it is very important to do at least an approximate and, based on the necessary parameters - no more, no less.
Dry run protection
To begin with, not every household pump is even afraid of dry running. If the pump parts are made of metal of sufficient thickness (and this thickness is not so large, about 1 mm), and not of technical polypropylene, then such a pump is not afraid of dry running. These pumps include - almost all vortex pumps (depending on the material of the impeller - impellers) and all monoblock.
All other pumps used in water supply, to one degree or another, need protection or dry-running control. And such protections are invented and industrially produced a great variety. They differ both in quality and price, and, most importantly, in the principles for determining the presence of a dry run.
The simplest and cheapest protections define dry running simply as a pressure drop at the pump outlet below a predetermined level. This is not entirely correct, but in some cases it saves. In this case, it is very important to correctly calculate the protection threshold, which, as a rule, can be adjusted.
More advanced ones have a delay in the protection response time, measuring either the pressure build-up time or the pressure loss time.
The best devices really detect the presence of water flow through the pump different ways: using a float, electromechanically (small impeller) or by pressure drop on a special membrane. However, they all have their own advantages and disadvantages. All of them have their own characteristics in the application and configuration.
Which device to install to protect your pump from dry running and whether to install it at all depends on the specific operating conditions of the pump and the parameters of your water supply system. Because a dry run, as we determined in the course of our conversation, is, in fact, violation of the pump operation
, and not the absence of water in it or at the exit from it. And in order to catch this violation and turn off the pump, the dry-running protection must be set accordingly.
What kind of protection to select depending on certain conditions, how to deal with the inadequate operation of the protection against dry running in the electronic control units of pumping stations and how to set up protection, and in some cases “cheat”, depending on the principle of determining the protection of dry move - we'll talk about this some other time.
Well, that's about all for today. Until we meet again, dear readers, on the pages of the blog