How Does a Liquid Level Relay Control the Water Level?

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A liquid level relay is an automated component used to control the liquid level. It mainly achieves the control of the water level by cooperating with a liquid level sensor and utilizing the electromagnetic principle and circuit control. The following is the specific working process of how it controls the water level:
### Working Principle
- **Float-type Liquid Level Relay**: A float-type liquid level relay usually consists of a float and a reed switch. The float floats up or down with the rise or fall of the water level. When the water level rises, the float also rises. When the set high water level is reached, the magnet inside the float approaches the reed switch, causing the contacts inside the reed switch to close. At this time, the normally open contacts of the liquid level relay close, and the normally closed contacts open. Through the change in the state of these contacts, the circuit of devices such as water pumps is controlled, thus stopping the injection of water into the container. When the water level drops and the float drops to the set low water level, the magnet inside the float moves away from the reed switch, and the contacts of the reed switch return to their initial state. The normally open contacts of the liquid level relay open, and the normally closed contacts close. The control circuit acts to start devices such as water pumps to inject water into the container, thus achieving the control of the water level.
- **Electrode-type Liquid Level Relay**: The electrode-type liquid level relay works by utilizing the conductivity of water. Several electrodes are installed inside the container, corresponding to different water level control points such as the low water level and the high water level. When the water level rises and touches the high water level electrode, water, as a conductor, forms a circuit between the high water level electrode and the common electrode. After the liquid level relay detects this signal, the control circuit acts to stop the operation of the water inlet device. When the water level drops and is lower than the low water level electrode, the circuit between the low water level electrode and the common electrode is disconnected. The control circuit of the liquid level relay makes a corresponding action to start the water inlet device, thereby maintaining the water level within the set range.
- **Pressure-type Liquid Level Relay**: The pressure-type liquid level relay works based on the principle that the liquid pressure is proportional to the liquid level height. A pressure sensor is installed at the bottom or side of the container. When the water level rises, the pressure exerted by the liquid on the pressure sensor increases. The pressure sensor converts the pressure signal into an electrical signal and transmits it to the liquid level relay. When the pressure signal reaches the set value corresponding to the high water level, the control circuit of the liquid level relay acts to stop the water inlet. When the water level drops and the pressure decreases to the set value corresponding to the low water level, the control circuit of the liquid level relay starts the water inlet device again, thus achieving the control of the water level.
### Control Circuit Connection
- The liquid level relay needs to form a complete control circuit together with executing devices such as water pumps and the power supply. Taking the control of a water pump by a common float-type liquid level relay as an example, the output contacts of the liquid level relay are usually connected in series with the coil of a contactor, and the main contacts of the contactor are connected to the power supply wires of the water pump motor. When the contacts of the liquid level relay act due to the change in the water level, they will control the energization or de-energization of the contactor coil, and then control the closing or opening of the main contacts of the contactor, achieving the start and stop control of the water pump motor and achieving the purpose of controlling the water level.