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 of 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 of 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 down.
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 at individual types of 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 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 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 foot valve or suction screen of the pump.
A float switch can be used to protect drainage and well pumps. To protect pumping units operated in network pipelines or wells, other automatic units must be used.
Relay and pressure sensor
To determine the pressure level at the outlet pipe, a pressure switch and a pressure sensor operate. The relay sets the minimum permissible pressure rate - 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.
Wider range of action for 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 water flow pressure 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. It 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 (low 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 for emergency modes is the 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 against emergency situations, small dimensions and power 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.
Dry running is the operation of the pump without liquid. For most models, this mode is extremely undesirable and can lead to failure. Let's figure out how to protect the pump from dry running.
The pump is a necessary part of the water supply system for a private home. But in order for the pump to work for a long time, it must be turned on and off periodically, preventing operation without water. To protect the pump from dry operation, several technical solutions have been invented. Let's get acquainted with their advantages and disadvantages and choose the best method of protection against dry running.
What is dry running
Most models are not designed to operate the pump in conditions where there is no water. This type of operation is called dry (sometimes idle, which is not entirely correct) running.
Most manufacturers explicitly state in their instruction manuals that dry running is not acceptable.
Let's figure out the reasons for this phenomenon and why it should not be allowed.
No matter where the water comes from, a situation periodically arises when the water runs out. For example:
- If the well's flow rate is small, it can simply be emptied during large-scale analysis. It will take some time for the well to fill again.
- If the pump is located on the surface, the pipe through which water is pumped from the well may become clogged.
- If water is supplied centrally, it may run out of water in the main due to a pipe break or technical work on the line that involves a temporary interruption of supply.
Why is dry running unacceptable in pump operation? The fact is that in most models, the water pumped out of the well plays the role of a coolant. In the absence of water, the parts begin to rub against each other more intensely, and as a result they heat up. The process then develops as follows:
- Heating parts expand and increase in size. Heat is conducted by the metal and to adjacent nodes.
- Parts begin to deform.
- The mechanism jams due to changes in the shapes and sizes of parts.
- In the electrical part, due to a sharp surge in voltage when the mechanical part stops, the motor windings burn out.
For the pump to break irreversibly, five minutes of dry operation is enough. Therefore, dry-running protection is a necessary component of any pumping station.
When calling for service, technicians can easily diagnose dry running as the cause of a breakdown - because of this, a number of characteristic distortions of parts occur in the mechanism.
Dry operation in most cases is grounds for refusal of warranty service.
How to protect a pumping station from running dry
Today, several solutions have been developed that will protect the pump from dry running by turning it off when the water supply is stopped. Each of these solutions has its own strengths and weaknesses, so the optimal effect is achieved by several protection systems combined together.
But to determine how to create effective dry-running protection for your pump, you must first find out what features are typical for individual components.
Protection relay
This is a fairly simple mechanism in design. It reacts to the water pressure in the system. As soon as the pressure drops below the permissible norm (this is a signal that water has stopped flowing into the pump), the device closes the electrical contact and the pump’s power circuit is broken. When pressure is restored, the circuit closes again.
Depending on the model and settings set by the manufacturer, the relay is capable of operating from a pressure drop from 0.6 (highest sensitivity) to 0.1 (least sensitivity) atmospheres. Typically, this sensitivity is quite enough to detect the occurrence of an idle situation and turn off the pump.
This mechanism is most common for pumps located on the surface. But some models have a housing protected from water getting inside and can be mounted on deep pumps.
It is not recommended to install such a device if the system has a hydraulic accumulator (HA). The fact is that usually in this case the installation of the protection device looks like this: “pump - check valve - protective relay - water pressure switch - GA”. This scheme does not provide 100% confidence that the pump will turn off when running dry, since the water contained in the accumulator can create a pressure of 1.4 - 1.6 atmospheres, which will be perceived as normal.
And then, if, for example, at night someone flushed the water in the tank and washed their hands, this will turn on the pump, but will not empty the water pump. And if water does not flow from the well for some reason, then by morning the pump will burn out due to dry running. Therefore, for systems with a hydraulic accumulator, it is better to look for other solutions to provide protection.
Water flow control
To determine whether there is water flow through the system, two types of sensors are used:
- Paddle relays are the simplest in design. In them, the flow of water bends the plate, which, in the absence of pressure, will straighten out and bridge the relay contacts. Then the circuit supplying electricity to the pump will turn off.
- The turbine relay is more advanced, but more complex in design. Its main element is a small turbine mounted on a shaft. The current makes it rotate, and the sensor reads the pulses created by an electromagnet attached to the turbine axis. If the number of pulses falls below the reference value, the circuit is switched off.
There are also combined water flow controllers. They may additionally include a pressure gauge, a check valve, a membrane relay to protect against a drop in water pressure and other components.
Such blocks are the most reliable, but due to the technical complexity, the cost of such a block can be quite significant.
Water level sensors
The water level sensor is placed in the shaft. It is most often installed in conjunction with a submersible pump, but there are models designed for use with above-ground pumping stations.
By design, there are two types:
In addition to the described mechanisms, there are many other systems to prevent dry running, for example, frequency converters. But these solutions are not used on home plumbing because they are too expensive, bulky or consume too much electricity.
Required tools and materials
To connect the pressure switch and dry running protection relay, you will need to prepare:
- The relays themselves.
- Tools for working with electrical wires: contact stripping knife, screwdrivers.
- Wires to create an electrical circuit.
- Keys for installing relays on highways.
- Means for sealing connections: sealants, rubber gaskets (usually included with the relay).
Having prepared everything you need, you can start working.
Installing protection against dry running of the pump yourself. Step-by-step instruction
You can see the connection diagram for the pressure switch and dry run protection in the figure:
The installation procedure is as follows:
After this, all that remains is to test the system, make sure that the relay does not interfere with the normal operation of the pump and properly turns it off after it goes dry.
Despite the fact that connecting any dry-running protection relay is not particularly difficult, there are some nuances, the understanding of which comes with the accumulation of practical experience. Therefore, it is especially important to listen to the recommendations of specialists in each case. Here's what professionals advise regarding the selection, installation and configuration of protective mechanisms against dry work:
- Before purchasing, carefully study the passport of the selected relay and make sure that its sensitivity and other characteristics are at the proper level for your well and pump. You can study the passport directly in the store or find it on the website of the manufacturer of the protective device and download it in pdf format.
- Make sure that all wires and elements of the circuits created are sufficient for the power used. Otherwise, there is a risk that the conductor or relay will burn out.
- The most advanced protection system may be powerless if used inappropriately. If any of the components operate, do not restart the pump until you have determined the cause of the problem and are sure it has been completely corrected.
- Remember that each relay requires periodic testing and replacement. Promptly replace expired protective system components.
In addition, we offer several videos so that you can see for yourself how to connect the relay:
Dry running protection is a precaution that should not be neglected when connecting the pump.
Although purchasing and installing the necessary devices requires some investment of time and money, these costs are much lower than the losses that will have to be incurred if the pump burns out.
Therefore, in most cases it is simply unreasonable to refuse to install protection.
The water supply system of a private home is impossible without a pump. But you have to somehow turn it on and off, and make sure that it doesn’t work in the absence of water. A water pressure switch is responsible for turning the pump on and off, and the presence of water should be monitored by protection against dry running of the pump. We will consider further how to implement this protection in different situations.
What is dry running of a pump?
No matter where the pump pumps water from, at times a situation arises that the water has run out - if the flow rate of a well or borehole is small, you can simply pump out all the water. If water is pumped from a centralized water supply, its supply may simply be stopped. The operation of the pump in the absence of water is called dry running. The term “idling” is sometimes used, although this is not entirely correct.
In order for the water supply at home to work normally, you need not only a pump, but also a dry water protection system and automatic on-off switching.
What's wrong with dry running, other than wasting electricity? If the pump operates in the absence of water, it will overheat and burn out - the pumped water is used to cool it. No water - no cooling. The engine will overheat and burn out. Therefore, protection against dry running of the pump is one of the components of the automation that will have to be purchased in addition. There are, however, models with built-in protection, but they are expensive. It is cheaper to buy additional automation.
How can you protect the pump from dry running?
There are several different devices that will turn off the pump if there is no water:
- dry running protection relay;
- water flow control devices;
- water level sensors (float switch and level control relay).
All these devices are designed for one thing - turn off the pump when there is no water. They just work differently and have different areas of application. Next, we will look at the features of their work and when they are most effective.
Dry running protection relay
A simple electromechanical device monitors the presence of pressure in the system. As soon as the pressure drops below the threshold, the power supply circuit is broken and the pump stops working.
The relay consists of a membrane that responds to pressure and a contact group that is normally open. When the pressure decreases, the membrane presses on the contacts, they close, turning off the power.
This is what protection against dry running of the pump looks like
When is it effective?
The pressure to which the device responds is from 0.1 atm to 0.6 atm (depending on factory settings). This situation is possible when there is little or no water, the filter is clogged, or the self-priming part is too high. In any case, this is a dry running condition and the pump must be turned off, which is what happens.
An idle speed protection relay is installed on the surface, although there are models in a sealed housing. It works normally in an irrigation scheme or any system without a hydraulic accumulator. It works more efficiently with surface pumps when a check valve is installed after the pump.
When it does not guarantee shutdown in the absence of water
You can install it in a system with HA, but you will not get 100% protection against dry running of the pump. It's all about the particular structure and operation of such a system. Place a protective relay in front of the water pressure switch and the hydraulic accumulator. In this case, there is usually a check valve between the pump and the protection, that is, the membrane is under pressure created by the hydraulic accumulator. This is a common scheme. But with this method of switching on, it is possible that a working pump in the absence of water will not turn off and will burn out.
For example, a dry running situation has been created: the pump is turned on, there is no water in the well/borehole/tank, and there is some water in the accumulator. Since the lower pressure threshold is usually set to about 1.4-1.6 atm, the protective relay membrane will not work. After all, there is pressure in the system. In this position, the membrane is pressed out, the pump will run dry.
It will stop either when it burns out or when most of the water supply is used up from the hydraulic accumulator. Only then will the pressure drop to critical and the relay will be able to operate. If such a situation arose during the active use of water, nothing terrible will happen in principle - several tens of liters will dry up quickly and everything will be normal. But if this happened at night, they flushed the water in the tank, washed their hands and went to bed. The pump turned on, but there was no signal to turn off. By the morning, when water collection begins, it will be inoperative. That is why in systems with hydraulic accumulators or pumping stations it is better to use other devices to protect against dry running of the water pump.
Water flow control devices
In any situation that causes the pump to run dry, there is insufficient or no water flow. There are devices that monitor this situation - relays and water flow controllers. Flow relays or sensors are electromechanical devices, controllers are electronic.
Flow relays (sensors)
There are two types of flow sensors - petal and turbine. Petal has a flexible plate that is located in the pipeline. In the absence of water flow, the plate deviates from its normal state, contacts are activated, turning off the power to the pump.
Turbine flow sensors are somewhat more complicated. The basis of the device is a small turbine with an electromagnet in the rotor. When there is a flow of water or gas, the turbine rotates, creating an electromagnetic field, which is converted into electromagnetic pulses read by the sensor. This sensor, depending on the number of pulses, turns on/off the power to the pump.
Flow controllers
Basically, these are devices that combine two functions: dry-running protection and a water pressure switch. In addition to these features, some models may have a built-in pressure gauge and check valve. These devices are also called electronic pressure switches. These devices cannot be called cheap, but they provide high-quality protection, serving several parameters at once, ensuring the required pressure in the system, turning off the equipment when there is insufficient water flow.
| Name | Functions | Dry running protection parameters | Connection dimensions | Manufacturer country | Price |
|---|---|---|---|---|---|
| BRIO 2000M Italtecnica | Pressure switch + flow sensor | 7-15 sec | 1" (25 mm) | Italy | 45$ |
| AQUAROBOT TURBIPRESS | Pressure switch + flow switch | 0.5 l/min | 1" (25 mm) | 75$ | |
| AL-KO | Pressure switch + check valve + dry-running protection | 45 sec | 1" (25 mm) | Germany | 68$ |
| Gilex automation unit | Pressure switch + idle protection + pressure gauge | 1" (25 mm) | Russia | 38$ | |
| Aquario automation unit | Pressure switch + idle protection + pressure gauge + check valve | 1" (25 mm) | Italy | 50$ |
In the case of using an automation unit, the hydraulic accumulator is an extra device. The system works perfectly when a flow appears - the opening of a tap, the activation of household appliances, etc. But this is if the pressure reserve is small. If the gap is large, both a HA and a pressure switch are needed. The fact is that the pump shutdown limit in the automation unit is not adjustable. The pump will turn off only when it has created maximum pressure. If it is taken with a large headroom, it can create excess pressure (optimal - no more than 3-4 atm, anything higher leads to premature wear of the system). Therefore, after the automation unit there is a hydraulic accumulator. This scheme makes it possible to regulate the pressure at which the pump turns off.
Water level sensors
These sensors are installed in a well, borehole, or container. It is advisable to use them with submersible pumps, although they are compatible with surface pumps. There are two types of sensors - float and electronic.
Float
There are two types of water level sensors - for filling the container (protection against overflow) and for emptying - just protection against dry running. The second option is ours, the first is needed when filling out. There are also models that can work either way, but the principle of operation depends on the connection diagram (included in the instructions).
The principle of operation when used to protect against dry running is simple: as long as there is water, the float sensor is raised up, the pump can operate, as soon as the water level has dropped so much that the sensor has dropped, the contactor opens the pump power circuit, it cannot turn on until until the water level rises. To protect the pump from idling, the float cable is connected to the open phase wire.
Level control relay
These devices can be used not only to control the minimum water level and dry running in a well, well or storage tank. They can also control overflow (overflow), which is often necessary when there is a storage tank in the system, from which water is then pumped into the house or when organizing a water supply for a swimming pool.
Electrodes are lowered into the water. Their number depends on the parameters they monitor. If you only need to monitor the presence of a sufficient amount of water, two sensors are enough. One - goes down to the level of the minimum possible level, the second - basic - is located slightly lower. The work uses the electrical conductivity of water: while both sensors are immersed in water, small currents flow between them. This means that there is enough water in the well/well/container. If there is no current, this means that the water has dropped below the minimum level sensor. This command opens the pump's power supply circuit and stops working.
These are the main ways in which protection against dry running of a pump is organized in the water supply systems of a private home. There are also frequency converters, but they are expensive, so it is advisable to use them in large systems with powerful pumps. There they quickly pay for themselves due to energy savings.
First, let's go over the theory, answer the question: “why do you need a dry-running protection relay for a well pump?”, and then we’ll look at the operating principle and how this relay is connected.
Dry running of a pump is a condition in which the pump runs idle, without water. In this state, the pump quickly overheats and can fail in a matter of minutes. To ensure safe operation of the pump, a dry-running protection relay was invented.
Let's take a quick look at what can cause a pump to run dry:
- When the pump power is incorrectly selected - for example, a high-capacity pump is selected that pumps out all the water from the well.
- When the water level in the well naturally drops.
- Leaking water pipe.
Operating principle 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 for turning off the pump and two springs for regulating the shutdown pressure.
When the water in the water pipe disappears, 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 of electric current to the pump.
The relay is reactivated by pressing the safety button. The contacts close, thereby assembling a circuit to turn on the pump, which creates the necessary pressure in the system, which is within 1 - 1.5 atmospheres. At this pressure in the system, the contacts of the dry running relay will be constantly closed.
Adjusting the relay operation
At the factory, the dry running relay is set to a pressure of 0.5 - 0.8 atm. At this pressure, the contacts will open and turn off the pump.
Let's consider the process of adjusting the shutdown pressure using the LP/3 relay as an example. To do this, you need to do a number of operations:
- Disconnect the power supply to the pump.
- Open the relay protective cover.
- Turn the nut clockwise on the small spring, thereby increasing the initial activation pressure.
- On the large spring, tightening the nut clockwise will raise the pump shutdown pressure.
- After adjusting the relay, we need to determine the shutdown pressure: to do this, it is necessary to analyze the water in the system, for example, open the faucet in the sink; as the water supply system empties, the water pressure will decrease. Use a pressure gauge to track at what pressure the relay contacts open. There should be a click and the safety button will come out of the housing.
With these 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:
- Supplying water to the system
- Exit to hydraulic accumulator
- Pressure gauge output
- Output for connecting a dry running relay
- Water exiting the system.
This can be clearly seen in the following figure:
Since the dry running relay works in conjunction with pressure relay then the electrical diagram for connecting these relays looks like this.
A dry-running protection relay is required to be installed, as it guarantees a long service life of the pump. If the pump fails due to dry operation, it is considered out of warranty!
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Any electric pump that pumps water from a well or borehole functions normally only if there is a working medium. Water for this mechanism is both lubrication and cooling. If the pump-pump unit runs idle, it may become unusable after just a few minutes. The dry running sensor for the pump is designed to monitor the presence of water flowing through the pump. At his command, the power supplied to the pump should be turned off in the absence of water.
So, dry running is the most common cause of pump failure. Moreover, in this case it will not even be possible to carry out warranty repairs if the examination proves this cause of the breakdown. This problem can happen in the following situations:
- Incorrect choice of height for hanging the pump in a well or well. This can happen if the depth of the water container has not been measured in advance. When the pump pumps out water to the level of its location, it will begin to capture air, resulting in overheating of the electric motor.
- The amount of water in the source naturally decreased. For example, the well (well) silted up or the water simply did not have time to get into the well after the last pumping. After completely pumping water out of the well, you must wait a certain time to fill the well.
- If a surface pump is used, which is located on the water surface, then the reason for its failure may be different. There are frequent cases when the suction pipe of the pump loses its tightness. Water is sucked in along with air, resulting in the pump motor not receiving sufficient cooling.
So, if there is no protection of the well pump from dry running, then the pump overheats and burns out. This applies not only to the electric motor. Modern pumps have a large number of plastic parts. Plastic, in the absence of cooling and lubrication, can also become deformed. This will first lead to a decrease in the performance of the device, and then cause it to overheat, jam the shaft and cause engine failure. Craftsmen are familiar with this type of failure, which occurs as a result of overheating. Having disassembled the unit, you can easily find those parts that have undergone overheating.
Types of dry running sensors and features of their operation
Expensive pump models already have built-in dry-running protection sensors. In particular, all pumps from the manufacturer Grundfos are already initially equipped with similar sensors. When operating cheaper units, a dry-running sensor for the submersible pump must be installed additionally. Let's try to understand the intricacies of the design and operation of dry running sensors of various types.
Water level sensors
1. Float switch. The connection diagram for the dry running sensor for the pump must be arranged so that its contacts are included in the power supply circuit of the pump motor. The float is afloat. When the water level drops, the float changes its location and its contacts automatically open, causing power to the pump to turn off. This is the simplest type of protection, characterized by reliability and ease of operation. 
Tip: In order for the float to work on time, it must be adjusted correctly. It is important that the pump body is still immersed in water when the sensor is triggered.
2. Water level control sensor. Let's take a closer look at this dry-running sensor for a pump and its operating principle. This is a relay consisting of two separate sensors lowered to different depths. One of them is immersed to the minimum possible level of pump operation. The second sensor is located slightly lower. When both sensors are underwater, a small current flows between them. If the water level decreases below the minimum value, the current stops flowing, the sensor is activated and opens the power circuit.
Sensors that monitor the water level are good because they allow you to turn off the pump even before the unit body is above the surface of the water. Consequently, the equipment is reliably protected from damage.
Protection relay
This is an electromechanical device that controls the pressure of water flowing through the pump. When the pressure drops, the pump power circuit opens. The pump dry running protection relay consists of a membrane, a contact group and several wires.
The membrane monitors water pressure. In the working position it is open. When the pressure drops, the membrane compresses the relay contacts. When the contacts close, the pump turns off. The membrane operates at a pressure of 0.1-0.6 atmospheres. The exact value depends on the settings. A drop in pressure to this level indicates the presence of the following problems:
- The water pressure has dropped to its minimum value. This can happen for several reasons. Including loss of performance by the pump itself due to exhaustion of its resource;
- the pump filter is clogged;
- the pump was above the water level, causing the pressure to drop to zero.
The protection relay can be built into the pump housing or mounted on the surface as a separate element. If the water pumping system includes a hydraulic accumulator, then a protective relay is installed together with a pressure switch, in front of the hydraulic accumulator.
Water flow and pressure sensors
There are 2 types of sensors that monitor the passage of the working medium through the pump unit and provide protection against dry running of the pump. These are flow switches and flow controllers, which will be discussed below.
1. The flow switch is an electromechanical type device. They come in turbine and petal types. The principle of their operation also differs:
- Turbine relays have an electromagnet in their rotor that produces an electromagnetic field as water passes through the turbine. Special sensors read the electrical impulses generated by the turbine. When the pulses disappear, the sensor turns off the pump from power;
- Paddle relays have a flexible plate. If water does not enter the pump, the plate deviates from its original position, causing the mechanical contacts of the relay to open. In this case, the power supply to the pump is interrupted. This relay option is characterized by its simple design and affordable cost.
Example of a flow sensor 
Such units turn off the pumping equipment if there is no water flow and turn it on if the pressure in the system drops below a predetermined level 2. Flow controllers (automation unit, press control). These are electronic devices that simultaneously monitor several important parameters of water flow. They monitor water pressure, signal when its flow stops, and automatically turn the pump on and off. Many devices are equipped with . High reliability also determined the high cost of these devices.
Which protection should you choose?
Selecting the right type of protective device is not easy. Several factors must be taken into account simultaneously:
- depth of water tank;
- well diameter;
- features of the pumping equipment used. For example, a submersible or surface pump is used;
- your financial capabilities.
For example, the simplest and cheapest means of protecting a pump from dry running is a float sensor. However, it must be taken into account that its use in a small diameter well is impossible. But for a well it is ideal.
If the water in the working container is known to be clean, then the best option would be to use a water level sensor. If you are not sure of the quality of the water supplied to the pump, it is better to use a flow switch or water pressure sensor.
Note: If there is a possibility that the pump filter is clogged with debris or dirt, then it is not advisable to use a level sensor. It will show the normal water level, although no water will be supplied to the pumping unit. The result will be a burnout of the pump motor.
A small conclusion can be drawn. You can use a pump without dry-running protection only if it is possible to constantly monitor the flow of water from a well or well. In this case, you can quickly turn off the power to the pump if the water stops flowing from the source. In all other cases, it is better to play it safe by installing a protective sensor. Its price is well worth it, considering the cost of purchasing a new pump to replace burned-out equipment.