Series and parallel installation scheme of pumps

Series installation

Series installation of pumps is used in two cases:

• One pump cannot provide the required pressure, and replacing it with a more powerful one is impractical.
• Due to the conditions of the technological process, there is a need for a short-term increase in head, and installing a more powerful pump with a frequency converter is impractical.

Series connection of two pumps with the same characteristics allows creating a mode with twice the head, while the flow rate remains the same as when one pump is working.

Series installation of pumps with different characteristics should be checked by calculation, since there is a possibility that a more powerful pump will create too high a flow rate, and not coping with it, a less powerful pump will turn into hydraulic resistance in the path of the flow.

Parallel installation

The parallel installation scheme of pumps is used in the following cases:

• One pump cannot provide the required flow rate, and replacing it with a more powerful one is impractical.
• According to the conditions of the technological process, there is a need for a short-term increase in flow rate, and the installation of one more powerful pump with a speed regulator is impractical.
• It is necessary to gradually increase the flow rate, which is often used in pump stations for water supply systems with high peak flows.
• For the purpose of increasing reliability, in such cases, the second pump serves as a backup.

Parallel connection of two identical pumps results in a mode with doubled flow rate, while the head remains the same as when operating with a single pump.

Parallel connection of pumps with different characteristics to a single head collector should be carefully checked by calculation, as there is a possible operating mode in which the more powerful pump creates too high a pressure in the head pipeline, which the less powerful pump cannot resist, allowing the flow to pass in the reverse direction.

To prevent reverse flow at the head connection of each parallel-connected pump, a check valve should be installed, and pumps should be selected with similar characteristics.

Regardless of the pump installation scheme, it is important to remember that increasing flow rate in a circulation system with a constant hydraulic resistance (such as a heating system) will result in a quadratic increase in head loss. For example, doubling the flow rate (pump delivery) in the circulation system will increase head loss in it by 4 times, while doubling the head will increase flow rate in the circulation system by 1.4 times (1.4 is the square root of two).

Therefore, the parallel and series connection of two pumps shown above did not result in a significant increase in flow rate in the circulation system. The hydraulic characteristic of the circulation system on the head-flow characteristic of the pump is represented in the form of a parabola.

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