A pump is a special mechanism for creating and controlling fluid flows in pipelines for various purposes. In order for the pump to work, it must be connected to the appropriate drive. Drives are divided into manual, mechanical, electrical. The mechanism connected to the electric motor is an electric pump (the most common in both industrial and domestic applications).
Basic requirements for the pump
The operating mode of the pump should provide all the requirements for the network in which it is included. Most often, this is the “on-off” function (when filling or pumping liquid in containers), maintaining the necessary pressure while increasing or decreasing the volume of consumption, uninterrupted operation in the circulation mode, emergency shutdown, connecting the backup pump. Fulfillment of these requirements is the key to cost-effective work, extending the life of equipment.
What the automation system consists of
To control operating modes, automation is being developed for pumps, which eliminates human intervention in the operating mode. Typically, the control circuit provides a transition to "manual mode" in the event of an emergency (for example, the failure of any sensor that is part of the automation). As a rule, automation for pumps includes the following elements:
1. A pressure switch is an aneroid-membrane device that, when a certain pressure is reached, closes or opens the electrical control circuits .
2. Electrocontact manometers (ECM) with movable and fixed electric groups. contacts.
3. Float system (installed in refillable containers) with el. contacts.
4. Pressure sensors with tansometric bridges that change the resistance for the passage of current when the pressure in the system changes.
5. Mechanical or electronic meters for the volume of fluid consumed, giving a signal in the control circuit when the set volume is reached.
6. Converters of frequency of the current supplying el. pump motor.
Elements 1, 2, 4, 5 are directly installed (crashed) into the pipeline. Automation for pumps also includes:
- electromagnetic starters;
- email schemes for switching to standby pumps;
- switching equipment for switching to the "AUT" or "MANUAL" mode;
- light fixtures signaling normal operation, emergency shutdown, transfer to reserve, etc .;
- electronic protection equipment pump motors, control circuits.
The above equipment is mounted in pump control cabinets in accordance with the requirements of the Electrical Installation Code (Electrical Installation Rules).
Principle of operation
How does automation work for pumps? Most often, the on-off mode of the pumps is found. For example: a tank (capacity) is filled with liquid to the desired level, while the float system closes (opens) the coil circuit of the electromagnetic starter, which turns the pump on (off). The same thing happens when lowering the float to a certain level. According to the same principle, automation works from a pressure switch, el. contact pressure gauge, liquid volume meters. To maintain the required pressure, the method of changing the frequency of rotation of the electric power is used. pump motor. This mode provides a frequency converter for the current supplying electric. pump. The frequency of the converter varies depending on the signal level from the pressure sensor. The continuity of fluid circulation in a closed circuit (this is mainly heating systems) is ensured by the presence of a backup pump, which is included in the emergency switching circuit when the main pump fails.