Joint Operation of Pumps

Joint operation of pumps is expedient in the following cases:

• One pump cannot provide the necessary flow rate or pressure, and replacing it with a more powerful one is impossible or irrational.
• According to the requirements of the technological process, there is a need for a peak increase in flow rate or head during operation.
• It is necessary to gradually increase the flow rate or head, which is often used in pumping stations for water supply systems with high peak flows.
• It is necessary to ensure high requirements for the reliability of the system.

Sequential scheme

The sequential scheme of pump installation is used when one pump cannot provide the required head. When two identical pumps are connected in series, their heads are added, while the flow rate remains the same as when one pump is operating.

Sequential connection of pumps with different flow rates can lead to a mode where the pump with a lower flow rate becomes a hydraulic resistance in the path of water flow, unable to handle the volume coming from the more powerful pump. Therefore, it is recommended to install pumps of equal power or thoroughly test the operation of the installation by calculating it for a specific system.

Parallel scheme

The parallel scheme of pump installation is used in systems with a gradual increase in flow rate and in cases where it is impossible to select one pump according to the given parameters. When two identical pumps are installed in parallel, their flow rates are added, while the head remains the same as when one pump is operating.

If there is a possible mode where only one pump will operate, check valves should be installed on the discharge pipes of each pump.

Parallel connection of several pumps of different power to one head collector can lead to a mode where the most powerful pump creates such a pressure in the collector that the less powerful pump cannot resist, allowing the flow to reverse. To avoid such modes, it is recommended to install pumps of the same brand or thoroughly model the operation of two pumps of different power for a specific system.

When two pumps are operating, it should be taken into account that an increase in flow rate in a circulation circuit with constant hydraulic resistance will lead to a quadratic increase in pressure losses in it. Thus, after increasing the water flow rate in the circulation circuit by 2 times, the pressure losses in it will increase by 4 times, and increasing the head by 2 times will lead to an increase in the flow rate in the system by 1.4 times (1.4 is the square root of two).

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