The design of the water pump is designed in such a way that the water pumped by it is used inside the device as a coolant and lubricant for rotating parts and assemblies. Therefore, if the pump unit operates without water, its service life will begin to decline sharply due to the abrasion of these parts and assemblies. The situation today can be resolved without problems. There are several options - connecting a dry running relay to a pumping station, installing a sensor, float switch or pressure switch.
Dry running relay
The relay is an electromechanical device of the simplest type, inside which a sensitive membrane is installed. It reacts to the pressure inside the water supply network. The dry-running device itself is installed after the pump, connecting both with a pipe fitting.
The principle of operation of the relay is that the membrane bends under water pressure. She presses on a pair of contacts, which rise and press against the other pair. An electrical circuit closes, from which the pump is powered. The relay in this case performs the functions of a conventional switch.
As soon as the pressure inside the water supply begins to drop and reaches a certain level, the membrane returns to its original position. The contacts open, that is, the power supply to the pumping unit is cut off. The latter stops working. A drop in pressure can happen in two cases:
- lack of water in the reservoir (well, well), from which water is taken;
- insufficient amount of fluid;
- clogged filters;
- wrong location (high) of the suction pipe or hose.
If a dry-running relay is not installed on the pump, the water pumping unit will quickly fail. The reason is the strong heating of the rotating parts, plus the lack of lubrication, which will lead to sticking of metal assemblies to each other or breaking them. This is especially true for bearings that support a rotating shaft. The latter has an impeller - a working body that is responsible for pumping water.
There is one nuance that concerns the installation of the relay, depending on the type of pump used. For example, after pumping stations, this dry-running protection device cannot be installed, since the hydraulic accumulator, which is an integral part of the station, constantly maintains the pressure inside the water supply network located after the device.
If a relay is installed after the HC, it will always be under pressure. Regardless of whether there is water in the supply tank or not, the pump motor will run all the time, because the membrane in the relay is in a bent state. Contacts are always pressed together. The pump does not turn off, even if it does not pump enough water.
The process may not last long, but even this time is enough to reduce the operating life of the pumping station. In this situation, the fluid flow sensor can solve the dry running problem.
Dry running sensor
The device is presented on the market in two versions: electromechanical and electronic. The latter are called controllers.
Electromechanical
There are two designs in this category: petal and turbine. The former are somewhat reminiscent of a membrane relay, only instead of a membrane, a metal plate is installed here.In the presence of water pressure inside the water supply system, it bends and closes the contacts for connecting the power supply of the electric motor. As soon as the pressure drops below a certain level or disappears altogether, the plate expands, opening the electrical contacts, that is, it stops the pump.
The turbine model of the dry running sensor is so named because there is a small turbine inside the device. It rotates under the action of moving water, creating an electromagnetic field, because the turbine rotor is an electromagnet. The field generated by the rotation sends out electrical impulses, which are picked up by a specially installed sensor. Depending on how many pulses the sensor receives per unit of time, the system itself decides to turn on or off the pump.
Electronic
This type of sensor performs two functions at once: it works as a pressure switch and protects the pump from dry running, that is, it replaces the fluid flow switch. There is no mechanical part in them, so these devices work much more accurately and longer. But their price is higher than all the others.
It is recommended to install electronic devices in water supply networks, in which pumps are installed with a small margin of pressure. If the headroom is large, it is better to use a separate pressure sensor, which is installed after the pumping equipment.
Float switch
The pump dry-running protection is only installed in downhole or submersible models. At pumping stations and surface units, the float is not mounted, here it is useless.
The principle of operation of the device is that when the water level in the well is high, the float is in the upper position, closing the electrical contacts through the lever. As soon as the water level begins to fall, the float descends, opening the contacts of the trigger mechanism.
Electronic relays
The electronic version of the pump dry-running protection relay is a new approach to solving the problem. Its main feature is contacts that sink into the water. In this case, the device itself is located separately from the water supply network and the pump.
Contacts can be lowered into a well or borehole. Then they work on the principle of determining the water level, so they are lowered below the water intake part of the pumping unit. Can be cut into the pipe of the water supply network. In this case, the device will work on the principle of a pressure sensor or a fluid flow switch.
The principle of operation of electronic relays is based on the use of water as a transmitter of electrical impulses. As long as there is water between the electrodes, which passes a current through itself, the electrical circuit is in a closed position. As soon as the water level falls, the electrodes are exposed, the circuit is opened - the pump motor remains without power.
The devices presented on the market make it possible to increase the time of trouble-free operation of pumping units. The purpose of dry-running sensors for a pumping station or individual pumps is the same - to prevent the unit from overheating. Sometimes, one installed relay is not enough to ensure the safe operation of the entire system, therefore, it is necessary to more carefully approach the design of an autonomous water supply system, taking into account the parameters of the supplied water. It is recommended, in addition to a relay or sensor, to install a check valve, a hydraulic accumulator and other protective devices.
