SERIES AND PARALLEL COMBINATION PUMP

Why do we need to connect number of pump?

A single pump may be insufficient to produce the performance required. Combining two pumps increases the pumping capacity of the system.

• Two pumps may be connected in series, so that water passes first through one pump and then through the second. When two pumps operate in series, the flow rate is the same as for a single pump but the total head is increased.

• Two pumps may be connected in parallel, so that half the flow passes through one of the pumps and the other half through the second pump. When two pumps operate in parallel the total head increase remains unchanged but the flow rate is increased.

Series Pumping

The discharge of one pump feeds the suction of a second pump. When two or more pumps are operated in series, the flow through all of the pumps is equal. Since whatever flows through one pump has to flow through the next pump in series, provided there are no side streams.

Purpose for pumping in series

1) One purpose for operating pumps in series is to insure that commercially available equipment can be used in a particular system, while at the same time reducing system costs.
2) The system with a long pipeline and a large amount of friction loss is across the entire pipeline.
3) This would result in a pump with an extremely high head, and thus an extremely high horsepower

Parallel pumping

The primary purpose of operating pumps in parallel is to allow a wider range of flow than would be possible with a single fixed speed pump for systems with widely varying flow demand.

Usually there are no more than three or four pumps operating in parallel

Examples of applications for parallel pumping include

• Municipal water supply 
• Wastewater pumps
• Pumps in water chilled heating, ventilating and air conditioning systems (HVAC)
• Main process pumps in variable capacity process plant
• Condensate pumps in a steam power plant