In pumps for domestic use, the main material of the impellers is thermoplastic (plastic, which is durable). It is characterized by great work potential and low cost. Material perfectly performs its functions for many years. But if it works without water, which acts as a lubricant and a source of heat removal, then the internal components of the pump undergo deformation. In extreme cases, jamming of the shaft and failure of the motor may occur. Usually, after this the pump cannot supply water, or it supplies it of very poor quality.
Who can diagnose a breakdown?
Dry running can be easily diagnosed by a specialist when disassembling a pump. It does not apply to warranty damage.
Rules to be followed
Any manufacturer of the device indicates that you cannot use the pump without water. Therefore, it is important to comply with certain standards, especially in places with a high level of risk.
The main reasons for the breakdown of the unit include the following:
- Wells and wells with a low rate of production. The dry run can be caused by the selection of the wrong pump configuration, which is distinguished by a high power level. Or the cause may be natural phenomena. For example, in hot summers, the water level in wells and boreholes drops, and their flow rate becomes lower than the rate of pump performance.
- The process of pumping water from containers. It is recommended to carefully monitor that the device does not pump out absolutely all the water, and turn it off in time.
- When pumping water from a network pipeline, the pump is cut directly into it. It helps to increase pressure. Since the pressure in the system is low, this is a fairly frequent application of the pumping station. It is very difficult to determine the moment when there is no water in the network.
Dry run protection is mandatory. When the container is empty, the device will not be able to turn off automatically. It will continue to function until it breaks, or until it is turned off by inattentive users.
Float
The pump is protected against dry running when pumping water by a float. The cost of such a switch is low.
The following types of device are distinguished:
- Devices that are designed only for filling the tank. Raising the water level to a certain limit causes the contacts to open inside the unit, and the pump system stops its work. This kind of floats serves as protection against transfusion, but not against dry running.
- Another modification involves working to empty the tanks. This is just what is required. The device cable is connected to the break of one of the phases that feeds the pump. The contacts inside the device open, and if the liquid level in the tank drops to a certain level, the pump will stop. The required response limit is determined by the installation location of the float. The cable of the device is fixed at a fixed level so that when the float is lowered at the moment the contacts open, there is still water in the tank. If water is pumped out of the well by a pump with a surface (self-priming) design, then fastening should be carried out in such a way that when the contacts open, the water level is above the grate, which absorbs water.
It should be noted that such protection of the pump against dry running is used in almost all wells with pumps. Devices are produced by various companies.
Unfortunately, the float is not versatile. In a well or network pipeline, it simply does not fit. Other types apply here.
Using a dry running pressure switch
The dry running protection relay of the pump is an ordinary device equipped with an additional function of opening the contacts when the pressure drops below the extreme level.
Typically, this level is set by the pump manufacturer and ranges from 0.4 to 0.6 bar. This indicator is not regulated. With proper operation, the pressure in the system will not drop below this mark, since all pumps used for private needs operate at high pressure.
Falling to the limit threshold can only be observed if there is no water in the pump. Without water, there is no pressure, and the relay, responding to a dry stroke, opens the contacts that power the device. The pump can only be started manually. Before this, the cause of the failure must be identified and eliminated. The pump is again filled with water before the next start.
What type of design is this pump guard designed for? Dry running of the pressure switch will help to avoid only an automatic configuration (together with a hydraulic tank). Otherwise, the operation of the device loses its meaning.
As a rule, the relay is designed for the deep configuration of the pump, as well as for the surface system or stations. It also protects the submersible pump against dry running.
Pressure switch equipped with pressure function
Many manufacturers propose replacing the hydraulic tank and pressure switch with another compact device - a flow switch, or press control. This device provides a command to start the pump when the pressure in the system drops to an indicator of 1.5-2.5 bar. After the water supply stops, the pump is turned off, since the liquid no longer passes through the relay.
Dry running of the pump is ensured by a sensor integrated in the relay. System shutdown occurs after fixing the dry run, which takes a little time and does not affect the functionality of the pump. In addition, press control provides protection against increased voltage in the mains.
The main advantage of the unit is its small size and weight. Unfortunately, the market is crowded with devices that are made unclear by which countries. Understanding the quality of a particular model is sometimes very difficult.
On average, the device works for about 1.5 years, provided that the assembly is carried out at a high level. The device, which has been certified and has high performance, is manufactured by ACTIVE. Its cost is about $ 100.
Using a level switch
The basis of the level switch is an electronic circuit board to which the dry-running protection sensors of the pump are connected. As a rule, the design of the device involves three electrodes, one of which performs a control function, and two - a working one. They are connected to the device through an ordinary single-core electric wire. Electrodes are used to signal.
The principle of operation of the device
Protection against dry running of the well pump is carried out by immersing the sensors in the tank at different levels. When water drops below the control sensor, which is installed slightly above the installation of the pump itself, the electrode transmits a signal to the level switch, and the pump stops working.
After raising the water above the control sensor, the pump automatics are activated. Dry run protection is characterized by a high level of reliability, but the cost of such a relay is much higher than that of other devices. The device is also used when pumping water from wells and boreholes. The level switch itself is installed indoors or in any place where there is no moisture.
Which device to choose?
The use of the device depends on the model of pump and the taste of the user. Experts note the following.
Protection against dry running of the downhole pump, as well as devices located in tanks or wells, will be fully implemented with the simultaneous use of a pressure switch and a float. These devices will complement each other. At a cost, this option will not be more expensive than installing an expensive level switch.
It should be noted that to protect the pump, designed for work in wells, more often resort to the use of pressure switches. It is better to use models of an expensive segment, as well as a level switch, which is distinguished by a high degree of reliability.
Note that the use of protective equipment is optional if:
• the well is deep and has a good flow rate indicated in the technical data sheet;
• You have proper experience using pumps in a well or well;
• You are sure that the water level in the system practically does not drop.
When operating the pump should be extremely careful. As soon as you notice that the water has disappeared or a thermal relay has tripped , which caused the pump to turn off, try to find out the cause of the incident, and only then activate the pump system.
Electrical modifications
Despite the fact that protective measures have been developed that operate on elementary principles and understandable criteria, it should be remembered that in addition to mechanical components (pipes, pressure switches, receivers, valves and valves), there are configurations that operate on electricity.
Do-it-yourself protection of the pump from dry running can be done by using relays, transistors, and resistors. The process is not particularly difficult.
But at present, a wide range of electronic devices is available on the market, and this greatly simplifies the task. There are even special automatic units that combine the function of a safety relay and a pressure switch. Some models perform a smooth restart of the pump.
For example, reviews indicate that the LC-22B model can cope with all the problems that arise in the pumping system promptly.
Users note the EASYPRO pressure controller from the Italian manufacturer Pedrollo. It provides maintaining a constant water pressure, automatically starts and stops the pump. The pressure regulator in this device is supplemented by an expansion tank and the function of changing the outlet pressure in the range from 1 to 5 bar. In addition, the device displays all the necessary information about the operation of the pumping system.
Conclusion
Applying your knowledge and skills when implementing a pumping system protection scheme is not so difficult. Any mechanical configuration is simple.
Having not only a theoretical base, but also knowledge of several solutions to this problem, you can ensure the smooth functioning of your pumping system.