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One of the most common reasons for pump damage is the so-called dry run. A dry run occurs when the pumped liquid does not flow through the pump, and air is drawn in instead. A lack of water leads to a sudden increase in internal temperature, which can have destructive consequences for some parts of the pump.
To protect the pump, we recommend installing a level sensor.
Conductivity probes operate on the principle of a closed electrical circuit and are an inexpensive and reliable protection against dry running. The advantage of this solution is that it shuts off the pump before it runs dry or starts drawing in air. In control units and control units with a frequency converter, the pump is shut off only after a few seconds of dry running.
From our range, we recommend the SHR-2 probes for level monitoring, or the SHR-3 switch HRH-7 and a two or three-core cable certified for drinking water from ELKO EP.
1. Pump Protection Against Dry Running Using Conductivity Probes
Conductivity probes protect submersible and sewage pumps against dry running when pumping out flooded areas.
The installation for pump protection against dry running consists of two SHR-2 probes, a HRH 7 switch, and a cable certified for use in drinking water installations. One probe determines the minimum level, while the other serves as a reference and must always be submerged. Once the water rises above the set minimum level, the HRH-7 switch activates the pump, which begins to pump out the water.
2. Well Level Monitoring
For controlling the pump in a well, we install 3 SHR-2 probes, a HRH 7 switch, and a cable certified for use in drinking water installations. The probes are installed at the desired minimum and maximum water levels. The third probe serves as a reference and is placed below the probe determining the minimum level. As the water level in the well decreases, the pump shuts off upon reaching the minimum level. Conversely, when the maximum level is reached through natural replenishment, the pump turns on and starts pumping again. We recommend level monitoring for all well pumps.
3. Refilling Water in Tanks
For refilling tanks, we recommend installing 2 SHR-3 probes and a HRH 7 switch. The probes are installed using a weld-on fitting or mounting nut at the minimum and maximum water levels, either on the tank wall or its lid. The probes can be positioned horizontally, vertically, or at an angle. The HRH-7 switch is connected to the probes with a two-core cable certified for use in drinking water installations. If the water falls below the minimum level, the probe activates the refill valve and fills the tank to the maximum level, where the valve closes. We recommend monitoring liquid leakage by installing a flood sensor on the floor near the tank. In the event of water leakage and electrode flooding, the switch activates a connected GSM Communicator, which sends a text message to your mobile phone.
More information about conductivity probes can be found here.
The electronic flow switch automatically turns the pump on and off. When the pressure in the system drops (i.e., when a tap is opened and water is drawn), the pump is turned off until 1/3 of the water from the pressure tank is used. At this point, the pressure switch activates the pump, which begins to replenish the missing water. After water use is finished (i.e., when the tap is closed), the pump does not turn off until it replenishes the water in the pressure tank to its original amount. If there is no water in the pump, the flow switch turns it off, thus protecting it from dry running.
It can only be used with centrifugal pumps, such as the Grundfos home waterworks MQ 3-45 or the Grundfos submersible well pump SB 3-45M. It cannot be used with vibrating and screw pumps.
From the range of flow switches, we recommend the automatic flow and pressure monitor Wilo HiCONTROL 1, which maintains constant pressure, protects the pump from dry running, and is virtually silent.
More information about the product can be found here.
The control unit with a frequency converter automatically turns the pump on and off. The device activates the pump when the pressure in the system drops (i.e., when a tap is opened and water is drawn) and gradually begins to replenish water into the system. After water use is finished (the tap is closed), the unit turns the pump off again.
For small water withdrawals, the frequency converter runs the pump at lower power, reducing electricity consumption.
If the pressure drops due to air intake, the control unit turns the pump off, protecting it from dry running.
It can only be used with centrifugal pumps and cannot be used with vibrating and screw pumps.
We recommend the control unit with a frequency converter Wilo SIRIO 3x230, which ensures that you do not experience a pressure drop during increased water use.
More information about the product can be found here.
In our e-shop, you can also purchase a pump from Grundfos with a built-in frequency converter SCALA 2, which continuously measures the pressure value at the outlet. If the pressure value falls below the required level, SCALA2 immediately increases the power and compensates for the pressure losses.
More about SCALA 2 can be found here.
The control unit automatically measures and calibrates the current draw (overload protection) and motor power factor (COS φ) after starting the pump, and stores the data after approximately 15 seconds.
The response to dry running protection is very fast, with the unit shutting off the pump after about 5-10 seconds when the pump starts drawing in air. The unit then signals a fault on the display. In this mode, the unit performs the first restart after 10 minutes (if there is still no water in the pump, then subsequently after 20, 40, 80, and 120 minutes). If the water column is restored during the restarts and the pump starts pumping normally, the system returns to normal operation. If there is still not enough water after 5 restarts (120 minutes), the system goes into fault mode, and the pump must be restarted manually.
It cannot be used with sewage, vibrating, and screw pumps.
From our range, we recommend the control unit CU 301, which is specially developed for submersible pumps SQE in applications where constant pressure must be maintained.
More information can be found here.
Float switches are mainly used for level monitoring and operate on a simple principle. The float is directly connected to the pump and is equipped with a tilt switch. If the pump is sufficiently submerged and the float is buoyant in a vertical position (ON), the contacts in the float are closed, and the pump can operate. When the water level drops to a certain point during pumping (OFF), the weight in the tilt switch opens the contacts, interrupting the power supply to the pump, which immediately shuts off.
Installation is recommended only if the space around the pump is large enough to allow the float to move freely.
It can be used with all types of pumps.
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