Parallel and Series Operation
Sub-basement SB-92. (Manual is available)
This experiment illustrates the basic operation and characteristics of centrifugal pumps.
The experiment will explore flow rates, pressure head, and efficiency of a single pump
and of two identical pumps that are run in series or in parallel.
In this experiment, there are two pumps connected through a pipe work that allows for
them to be operated individually, in series or in parallel.
When identical pumps are in series the pressure head is doubled but the flow rate remains
the same. This is useful when a high pressure is needed but the same flow rate as of a
single pump is sufficient. In this case however the second pump in the series must have
the ability to operate at a higher suction pressure, which is produced by the first pump.
When pumps are run in parallel the flow is increased and the pressure head produced is
around the same as a single pump (these are for identical pumps run in parallel like the
ones used in this experiment).3
Another concept illustrated in this lab is the efficiency of a pump. Energy can take
different forms and a part of engineering is transferring the most of one type of energy to
another and quantifying the efficiency. The energy in this experiment is actually put
through two transformations. First electrical energy, which is the energy put into the
system, is transferred to mechanical energy, which is the energy required to spin the shaft
and impeller. Second, the mechanical energy is transferred into energy of the fluid. This
is accomplished through the pumps rotation, which transfers the velocity energy of the
water to pressure energy. The overall efficiency is the product of the mechanical (shaft)
efficiency and the thermodynamic efficiency, as shown below:
Overall efficiency is calculated by: