Why is pump protection against dry running needed and how does it work? Dry running sensor for a water pump: varieties, principle of operation, connection diagram Protection against dry start of the pump
What is a "dry running" pump? This is an emergency mode of operation, in which the electric motor rotates, but water does not enter the pump or it does not enter in sufficient quantities. The design of the pump is such that the pumped medium plays the role of lubricating and cooling liquid in it. No cooling and lubrication - the electrical components of the engine overheat, moving parts are subject to increased wear. Without water, a running pump can fail in just a few minutes, a breakdown will be very expensive to repair. To exclude the possibility of functioning in emergency mode, it is necessary to protect the well pump from dry running.
For submersible pumps, dry running is due to the absence or insufficient amount of water at the level of the pump intake holes in the well or well. We list the reasons that can cause it:
- Water level drop below the critical level as a result of incorrect selection of the pump suspension height in the working string. An appropriate calculation of the dynamic level was not carried out or the well flow rate was incorrectly measured. With active water intake, the pump begins to “pick up” air.
The submersible pump must be located below the dynamic water level
- Degradation of a previously normally functioning well, as a result of which the amount of water that it can produce has decreased (the flow rate of the source has fallen).
If the source has not dried up completely, the water level temporarily drops, then recovers and the owners may not always notice that the equipment periodically operates in emergency mode.
If the well or well is shallow (up to 10 m), a surface pump can be used to supply water. In this case, a dry run may occur not only due to a drop in the water level. The cause may be a leak in the suction pipe or its blockage.
Equipment protection and financial costs
A little about money:
- Downhole vibration pump "Brook" or its equivalent costs about 3,000 rubles. Its protection against dry running will cost approximately the same amount if you do all the installation and connection work yourself. Does it make sense to invest in additional equipment with such a cheap pump?
The domestic "Brook" is cheap, so it's hardly worth spending money on protecting it
- Expensive borehole pumps are initially equipped with protection, and often multifunctional. For example, all Grundfos models have protection not only against dry running, but also against overload, overheating, power surges and reverse axial displacement. The cost of high-quality equipment from a good manufacturer includes the necessary automation to prevent its operation in emergency mode. Separately, there is no need to worry about protection, when mounting to the estimated depth, additional sensors are not needed - "all inclusive".
High-quality equipment is already equipped with the necessary automation, it does not need additional protection
- Mid-range equipment can also be protected from running without water. Dry running sensors can be located inside the housing or be remote. For wells, this does not matter, but for a narrow well, the built-in option is preferable, there is less risk of damage. As for the lower price category, here you need to carefully study the package, read the product passport. The cheaper the pump, the higher the chance that protection will be absent in it. It is available as an option for many models. In any case, before buying, you need to find out exactly from the seller whether there is protection against dry running in a particular model. If not, add the price of additional equipment and its installation to the cost of a cheap pump - you get the amount of real costs.
- Most complete waterworks, where a surface pump is used, have protective automation. However, here you should also be interested in the configuration of a particular model.
When is a well pump protected against dry running?
There are no regulatory requirements for private developers regarding the protection of equipment for individual water supply. It's up to you whether you spend money on it.
For those who can afford it, we recommend purchasing high-quality equipment, initially equipped with all the necessary automation. Entrust the installation to competent installers and sleep peacefully in the future, without encountering any problems.
For those who are forced to save, we suggest approaching the issue rationally. Do you always need additional protection for a downhole pump that is not originally equipped with it?
In our opinion, in the country, where the pump is used for watering and washing in manual mode and the owners always have the opportunity to notice that the water has stopped flowing from the pipe or hose, the protection of well pumps is not a strictly mandatory function. The power supply can be turned off by unplugging the power plug. Not very convenient, but free.
Another thing is if the water supply system operates in automatic mode. The automatic watering of the garden turns on when the owners are not at home, the large bathtub is filled, the washing machine or dishwasher is running at a time when all family members are watching TV. For those who want to have a comfortable residential building and not have problems with water supply, we advise you not to save money and install protection.
Expensive engineering equipment of a full-fledged individual residential building must be protected from emergency operation
Dry run protection
Perhaps one of our readers decides to select and install water supply equipment on their own. Do-it-yourself protection of a well pump from dry running can be performed using various technical solutions. Protection is provided by sensors (relays) that cut off the power supply before or after the emergency mode occurs. Let's see what dry running sensors are, how they work and how they are installed:
Water level measurement
The first group of sensors measures the water level in a well or well:
- Pressure switch that measures the dynamics of changes in the water level in the well. It consists of two sensors located at different levels. One monitors the minimum possible water level for the operation of the pump and turns off the power when it drops. The other is located at a level that guarantees a stable flow of water into the water intake. When the water rises to this mark, the pump will automatically turn on.
The electrical circuit of the dry-running protection relay, the signals come from two sensors located in the working string of the well
- A float sensor that measures the water level in a well. The sensor is located in a sealed air-filled casing (float), fixed on the body of the submersible pump. It floats in the water column above the water intake. When the water level drops, it goes down. When the mark overcomes the lower permissible limit, the water pressure on the float disappears, the relay opens the electrical circuit. If the equipment does not include additional automation, the pump with float protection must be turned on manually after it is triggered.
Float switches are practically non-existent on modern well pumps: there is simply no room for a float in a narrow casing pipe. But submersible pumps for wells, where there are no size restrictions, are very often equipped with float sensors.
Sensors and relays that measure the water level directly in the well and well are good because the pump is turned off even before the critical drop in water level. Thus, dry running is completely excluded and the equipment always operates in normal mode.
Pressure and flow sensors
Sensors that respond to the characteristics of the flow created by the pump are inferior to the water level control system in terms of efficiency. Flow and pressure sensors turn off the pump after the pumping of water has stopped. True, the period of work in emergency mode is short. However, this is not the best solution. But such protection of pumps for wells is cheaper, besides, their installation, repair and replacement, if such a need arises, is easier.
- Pressure sensor installed on the outlet pipe (supply pipe) after the pump. In general, the sensor is set to a value of 0.5 bar, a lower pressure with the pump motor running is considered critical. If the pressure value drops below, the electrical circuit opens. To control the pump (on-off) paired with a hydraulic accumulator, in any case, it is necessary to install a pressure switch. Often, the pressure switch is combined with a protection sensor in one device, which reduces the cost of automation.
Pressure sensors to turn on the pump and protect it from dry running are connected to the outlet pipe and the circuit supplying the electric motor in series
The pressure sensor has an adjustable spring design
- The flow sensor is also placed on the outlet pipe. The flow rate of water when the pump is running drops below the permissible value - it turns off.
The flow sensor determines the speed of water movement along the bend of the membrane (plate)
Pressure and flow sensors are not installed in the well, but in front of the entrance to the accumulator. Can be used with both submersible and surface pumps.
Dry running protection according to the electrical parameters of the pump
The sensors and relays listed above must be in direct contact with the pumped medium. There is a technical solution in which there is no need to mount measuring instruments in the working string or install them in the pipeline. Such well pump protection is based on reading the electrical parameters of the pump motor. When liquid enters the suction hole, the electric motor operates in normal mode and its power factor cos φ tends to the nominal value of 0.7 ... 0.8. Water stops flowing, pumping stops - cos φ drops to the level of 0.25 ... 0.4.
Graph of cos φ change depending on the pump operation mode
A special control relay, based on the parameters of voltage and current, calculates the power factor of the electric motor and switches it off if the value of cos φ drops below the critical value. Depending on the power of the pump motor and the relay model, the automation is connected directly or through a transformer. The reliability of this method of protection is quite high, but not all experts consider it 100%.
Motor power factor relay TELE G2CU400V10AL10 can be used in both single-phase and three-phase networks
How to choose the right dry run protection, which sensor or relay to install? There is no single answer to this question. Each of the technical solutions has its pros and cons. The depth of the well, the parameters of the pump, the presence of a hydraulic accumulator, the type of control automation, and equipment compatibility should be taken into account. It is possible and even desirable to duplicate the dry-running protection function in one system by various devices, provided that they are built on different principles for measuring parameters.
Video: 100% pump dry running protection
The video will be useful to those who plan to install water supply equipment on their own.
If you are not ready to study in depth the features of individual water supply yourself, we recommend entrusting the calculation of the necessary equipment parameters, its selection and installation to specialists. In this case, you can be sure that the protection of the well and expensive equipment is done at the proper level.
Dry running is the operation of a pump without liquid. For most models, this mode is highly undesirable and can lead to failure. We figure out how to protect the pump from dry running.
The pump is a necessary part of the water supply system of a private house. 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 devised. Let's get acquainted with their advantages and disadvantages and choose the best way to protect against dry running.
What is a dry run
Most models are not designed to operate the pump in the absence of water. Such work is called a dry (sometimes idle, which is not entirely correct) move.
Most manufacturers explicitly indicate in the instruction manuals that dry running is unacceptable.
Let's figure out what causes this phenomenon and why it should not be allowed.
Wherever the water comes from, periodically there is a situation when the water runs out. For example:
- If the well flow rate is small, with a large analysis, it can simply be emptied. It will take some time for the well to fill up 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 dry up in the mains due to pipe breaks or technical work on the line, associated with a temporary interruption of supply.
Why is dry running unacceptable in the operation of the pump? 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 intensively, as a result they heat up. Then the process develops as follows:
- Heating parts expand, increase in size. Heat is conducted by the metal to neighboring nodes.
- Details begin to deform.
- The mechanism jams due to changes in the shape and size of parts.
- In the electrical part, due to a sharp voltage surge, when the mechanical part stops, the motor windings burn out.
In order for the pump to break down irreversibly, five minutes of running “dry” is enough. Therefore, dry-running protection is a necessary component of any pumping station.
When contacting the service, the masters easily diagnose dry running as the cause of the breakdown - because of this, a number of characteristic distortions of parts occur in the mechanism.
Dry running is in most cases grounds for denial of service under warranty.
How to protect the 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 interrupted. Each of these solutions has its own strengths and weaknesses, so several protection systems combined together give the best effect.
But in order to determine how to create effective dry-running protection for your pump, you must first find out what features are characteristic of 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 the water has stopped flowing into the pump), the device closes the electrical contact, and the pump power circuit is broken. When the pressure is restored, the circuit closes again.
Depending on the model and the settings that the manufacturer has set, the relay is able to operate from a pressure drop from 0.6 (most sensitive) to 0.1 (least sensitive) of the atmosphere. Usually this sensitivity is enough to determine the occurrence of an idle situation and turn off the pump.
The most common such mechanism for pumps located on the surface. But some models have a housing protected from water ingress and can be mounted on deep pumps.
Such a device is not recommended to be installed if a hydraulic accumulator (HA) is provided in the system. 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". Such a scheme does not give 100% certainty that the pump will turn off during a dry run, since the water contained in the accumulator can create a pressure of 1.4 - 1.6 atmospheres, which will be taken as the norm.
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 GA. And if for some reason water does not come from the well, then by morning the pump will already burn out due to dry running. Therefore, for hydraulic accumulator systems, it is better to look for other solutions to provide protection.
Water flow control
To determine if there is water flow through the system, two types of sensors are used:
- The most simple in design are petal relays. In them, the flow of water bends the plate, which, in the absence of pressure, will unbend and bridge the relay contacts. Then the circuit that supplies electricity to the pump will turn off.
- The turbine relay is more perfect, but more complicated in design. Its main element is a small turbine mounted on a shaft. The flow makes it spin, and the sensor reads the pulses generated by an electromagnet attached to the axis of the turbine. 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 switch 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 with a submersible pump, but there are models designed for use with ground pumping stations.
There are two types of construction:
In addition to the mechanisms described, there are many other systems to prevent dry running, for example, frequency converters. But these solutions are not used on domestic plumbing because they are too expensive, bulky or consume too much electricity.
Necessary tools and materials
To connect a pressure switch and a dry-running protection relay, you will need to prepare:
- the relay itself.
- Tools for working with electrical wires: a knife for stripping contacts, screwdrivers.
- Wires to create an electrical circuit.
- Keys for mounting the relay on highways.
- Means of sealing connections: sealants, rubber gaskets (usually come with the relay).
Having prepared everything you need, you can get to work.
Do-it-yourself installation of protection against dry running of the pump. Step-by-step instruction
You can see the connection diagram of the pressure switch and protection against falling dry running in the figure:
The installation order is as follows:
After that, it remains only 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 going 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 is what professionals advise about the selection, installation and configuration of protective mechanisms against dry operation:
- Before buying, 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 examine the passport directly in the store or find it on the page of the manufacturer of the protective device and download it in pdf format.
- Make sure that all wires and elements of the created circuits are sufficient for the power used. Otherwise, there is a risk that the conductor or relay will burn out.
- The most perfect protection system can be powerless if used ineptly. If any of the components have tripped, do not turn on the pump again until the cause of the malfunction is found and you are sure that it has been completely eliminated.
- Remember that each relay requires periodic verification and replacement. Replace expired protective system components in a timely manner.
In addition, we offer several videos so that you can see with your own eyes how to connect the relay:
Dry running protection is a precaution that should not be neglected when connecting the pump.
Although the purchase and installation of the necessary devices requires some time and money, these costs are much lower than the losses that will have to be incurred if the pump burns out.
Therefore, it is simply unreasonable to refuse to install protection in most cases.
Often used in home water supply systems. But in order for it to be able to fully and, most importantly, function smoothly, it is important to protect the device as much as possible from possible overheating, etc. This can be achieved using certain protective elements (sensors) that prevent the pump from running dry. It is important to understand the principle of operation of these elements, as well as their connection schemes. This will be discussed further (for clarity, a video instruction is attached).
"Dry running": what is it, the reasons for its occurrence
"Dry running" is usually referred to as the operation of the pump without water. It is considered emergency and, accordingly, very dangerous for a device that pumps out water. The fact is that the lack of water is a threat to the functional elements of the pump, because it is a kind of cooler and performs a lubricating function. Even a short operation of the pump on a “dry run” (regardless of its type) is enough for it to fail ahead of schedule.
Advice. Some owners of water pumps are in no hurry to install protective elements that prevent the device from running idle (without water), but it would be worth it, because breakdowns resulting from dry running are not included in the number of warranty cases. So, you will have to do the repair at your own expense.
To begin with, it is worth understanding why insufficient water supply may occur:
- Poor pump selection. A typical problem when operating the device in a well. The absence of water is possible if the performance of the pump "interrupts" the well flow rate or the level of installation of the device is located above the dynamic water level.
- Blockage in the suction pipe.
Dry running relay
- Violation of the tightness of the water pipe.
- Low water pressure. If this problem occurs and the pump is not equipped with a dry-running protection system, it will run until it fails or is manually turned off.
- Lack of control over the water level in a drying up source.
Dry run protection devices: varieties, principle of operation
To prevent the possibility of a "dry run", several devices were created that differ in design and operation scheme:
Dry running sensor: connection diagram
The sensor is connected in two stages: mechanically and by connecting to the mains. First, the sensor is physically attached to the pump. Usually the device has a special socket.
Advice. Some pumps do not have this socket. As a replacement, you can use a brass tee, to which, by the way, you can connect a pressure gauge and even a hydraulic accumulator.
Before screwing the relay onto the tee or socket, the thread must be sealed. This can be done either with the help of a special (and rather expensive) thread, or linen.
Advice. For reliable fixation of the thread, its winding is carried out towards the end in a clockwise direction.
After winding the thread, you can begin to twist the relay. This must be done very carefully. When it goes tight, you need to tighten the relay with a wrench.
Now you can connect the sensor to the mains. First of all, find two groups of contacts on the sensor. In each group of wires, find the free ends and screw the wire strand to them. We connect the ground separately, attaching it to the screw on the relay.
Connected dry running sensor
Now you can connect the relay directly to the pump. A regular wire will do. We connect one end of it to the free wires of the relay, the other to the pump wires. Do not forget that the colors of the wires to be connected must match each other.
It remains only to check the operation of the system in action. We connect the pump to the mains and observe. If during the operation of the pump there is an increase in the indicator on the pressure gauge, and when the maximum allowable indicator on the sensor is reached, the pump turns off - the installation was carried out correctly. The device can be operated in real conditions.
This concludes our review of the existing types of protective devices for the water pump, as well as their connection diagrams. Be careful when installing the device. Good luck!
How to connect a dry running sensor: video
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 idling. 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 a breakdown 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 they are 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), which are installed at different heights 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 pressure sufficient for the safe operation of the 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 characteristics of the water supply device.
3.1 How to connect a dry-running relay to the pump? (video)
Modern pumping stations are often equipped with either a full-fledged dry-running protection, or at least protection against engine overheating. The benefit of having such elements in the design is obvious: where necessary, protection can prevent pump failure.
But the presence of protective modules leads to an increase in the cost of the structure. That is why it is worth considering in advance how important dry run protection is for you, and whether it is worth spending money on a more expensive station - such as.
The presence of a device that will turn off the pump when water stops flowing into the system is highly desirable in such cases:
- The pump is used to increase pressure by tapping the pumping station into the mains water supply. This is done quite often, and in order to insure the equipment in case of a water supply shutdown, protection is installed.
- The station is used to draw water from a reservoir. Here, the relevance of protection against “dry running” is obvious: as soon as the container is emptied, the pump will begin to “grab” air, and if it is not turned off in advance, it will quickly fail.
- A well or a well with a low debit is used as a source of autonomous water supply. Here, too, there is a risk that the hose with which the intake is carried out will be above the water level, and this will lead to breakage.
The latter case is relevant for almost all private households. In the summer, the water level drops anyway, but it is additionally lowered due to intensive selection for irrigation. So a pumping station pumping water from a well or a shallow well must be tediously protected.
Ways to implement protection
Dry running protection can be implemented in different ways. Here are the most common patterns.
float switches
A float is the simplest device that is used when equipping autonomous water supply systems based on tanks or wells:
- The float is fixed in such a way that the system works when the water is slightly above the level of the intake pipe.
- When the water level drops, the float opens the contacts.
- When the contacts open, the phase supplying the pump is broken, and the pump stops working.
Pressure/flow switch
Another device (example -), which is equipped with many pumping stations. It works quite simply:
- The manufacturer sets a certain pressure level at which the relay is activated. Usually this value does not exceed 0.5 -0.6 bar and cannot be changed by the owner of the pump.
- As soon as the pressure in the system drops below this level (and this does not happen even with intensive simultaneous water withdrawal), the relay registers a “dry run” and the pump is de-energized.
Note! Restart must be carried out in manual mode, after the cause of the relay operation has been eliminated and the system has been filled with water.
A prerequisite for the effective operation of the pressure switch is the presence of a hydraulic accumulator. However, automatic alluvial stations are completed initially.
If there is no accumulator, then a compact flow switch can be used instead of a pressure switch. But it works on a similar principle, but turns off the system when water passes through the device. The response time of such devices is short, so the pump receives effective protection.
Level switch
If the water source is a well, then a level switch can be used to protect the pump from "dry running":
- The relay is a board to which the electrodes are connected (usually two working and one control).
- The electrodes are lowered into the well and fixed in such a way that the control electrode is located just above the level of the well pump installation.
- As soon as the water level in the well drops, the control sensor is activated and the pump is turned off. After the water level rises, the system automatically starts on a relay signal.
