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The water supply system of a private house is impossible without a pump. But it must somehow be turned on and off, to ensure that it does not work in the absence of water. The water pressure switch is responsible for turning the pump on and off, and protection against dry running of the pump should monitor the presence of water. How to implement this protection in different situations and consider further.
What is a dry running pump
Wherever the pump pumps water, sometimes a situation arises that the water is over – with a small flow rate of a well or well, you can simply pump out all the water. If water is pumped from a centralized water supply, its supply can simply be stopped. The operation of the pump in the absence of water is called dry running. Sometimes the term “idling” is used, although this is not entirely correct.
What’s wrong with dry running, besides wasting electricity? If the pump runs without 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 the dry running of the pump is one of the components of automation that will have to be purchased. There are, however, models with built-in protection, but they are expensive. Cheaper to buy automation.
How can the pump be protected from running dry?
There are several different devices that will turn off the pump in the absence of water:
- dry run 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 in the absence of water. They just work differently and have different applications. Next, we will understand the features of their work and when they are most effective.
Dry run protection relay
A simple electromechanical device controls the presence of pressure in the system. As soon as the pressure drops below the threshold, the power circuit breaks, the pump stops working.
The relay consists of a membrane that reacts to pressure and a contact group that is normally open. When the pressure drops, the membrane presses on the contacts, they close, turning off the power.
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 at all, the filter is clogged, 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 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. Works more effectively with surface pumps when a check valve is installed downstream of the pump.
When it does not guarantee shutdown in the absence of water
You can put it in a system with GA, but you will not get 100% protection against dry running of the pump. It’s all about the features of the structure and operation of such a system. They put a protective relay in front of the water pressure switch and the 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 accumulator. This is the usual pattern. But with this method of switching on, a situation is possible when a running pump, in the absence of water, does not turn off and burns out.
For example, a dry running situation has been created: the pump has turned on, there is no water in the well / well / tank, there is some water in the accumulator. Since the lower pressure threshold is usually set on the order of 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 accumulator. Only then will the pressure drop to critical and the relay will be able to work. If such a situation arose during the active use of water, nothing terrible will happen in principle – a few tens of liters will run out quickly and everything will be fine. But if it happened at night, they let the water out of the tank, washed their hands and went to bed. The pump has turned on, there is no signal to turn off. By the morning, when the analysis of water begins, it will be inoperative. That is why in systems with hydroaccumulators or pumping stations it is better to use other devices to protect against the 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. Relays or flow sensors are electromechanical devices, controllers are electronic.
Relay (sensors) of the flow
There are two types of flow sensors – petal and turbine. Flap has a flexible plate that is in the pipeline. In the absence of water flow, the plate deviates from the normal state, contacts are activated that turn 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. In the presence of a flow of water or gas, the turbine rotates, an electromagnetic field is created, 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: protection against dry running and a water pressure switch. Some models, in addition to these features, 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, providing the pressure required in the system, turning off the equipment when there is insufficient water flow.
| Name | Functions | Parameters of operation of protection against dry running | Connecting 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 |
| Dzhileks 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, a hydraulic accumulator is an extra device. The system works perfectly on the appearance of a flow – the opening of a tap, the operation of household appliances, etc. But this is if the headroom is small. If the gap is large, both a GA and a pressure switch are needed. The fact is that the pump shutdown limit in the automation unit is not adjustable. The pump will only turn off when it reaches maximum pressure. If it is taken with a large margin of pressure, 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, they put a pressure switch and a hydraulic accumulator. This scheme makes it possible to regulate the pressure at which the pump is turned off.
Water level sensors
These sensors are installed in a well, borehole, tank. 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 tank (protection against overflows) and for emptying – just protection against dry running. The second option is ours, the first one is needed when filling the pool. There are also models that can work this way and that, and the principle of operation depends on the connection scheme (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 pulled up, the pump can work 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 a break in the 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 pool water supply.
Electrodes are lowered into the water. Their number depends on the parameters they track. If you only need to monitor the presence of a sufficient amount of water, two sensors are enough. One – falls to the level of the minimum possible level, the second – the base – is located a little 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 / tank. If there is no current, it means that the water has dropped below the minimum level sensor. This command opens the power supply circuit of the pump and it stops working.
These are the main ways in which protection against dry running of the pump is organized in the water supply systems of a private house. 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 off due to energy savings.