The In parallel pumps, loss of head

            The article discussed was about
cases in which water use located near pump stations needs to be taken into
consideration. It also explains on how to properly interpret and use a pipe
network model to be able to determine a system head curve for those said conditions.
Water engineers commonly give questions about how much water can a pump station
put out. This can be answered immediately by looking up the nominal discharge
of the pumps and assume these will operate in such flow; however, actual
discharge may vary as it only depends on the head difference across the pump
while it is running.

A pump or
several pumps in parallel can operate at any point along the pump’s head
characteristic curve. The rate of discharge in
the main line is equal to the sum of discharge in each of the parallel pipes.
In parallel pumps, loss of head in each parallel pipe is same as well. The
difference in head between the suction and discharge sides of a pump would give
the actual discharge. The relationship between this head difference and the
pump discharge is known as the system head curve. An intersection occurs
between the pump characteristic curve and the system head curve; this gives us
the discharge and head produced by a pump.

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            The effects of varying tank levels
and the operation of other pumps can be described in simple graphical
procedures to be able to determine the pump discharge. Moreover, when two tanks
are connected by pumps with a difference in length, diameter, and roughness, all connected in series, then the difference in water
surface levels is equal to the sum of head losses in all the sections.

conclude, an engineer who is supposed to select the pump and discharge line
must first evaluate the operating points for a range of water consumption
patterns, and not limited to just a range of tank levels and pump combinations.
When there is a large water use between the pumps and the downstream tank, it
is recommended not to add lift head and friction head because it may result to
an incorrect way of generating system head curves. On the other side of the
coin, generating system head curves can be done analytically by lumping water
users at a single node or by using a water distribution model, when used on a
more complex system, to determine system heads.