Page 94 - Know and Understand Centrifugal Pumps

Understanding Pump Curves

The information on the dash panel is located right in front of the eyes
of the operator of the car. It’s a shame that most pump operators don’t
have their control panel (the curve) before their eyes, or even within
reach, as they operate the pumps. This is the source of many problems
with pumps.

History
. .. ~
Some three thousand years ago, the ancient Romans and Greeks
understood the hydraulic laws that govern today’s modern pumps.
They had already calculated the physics and math required to bring
water from the mountain streams, down through giant aqueducts and
underground clay pipes, and spray a stream of water 12 fi up into the
air in the fountain at the public square. They understood the laws of
gravity and the concept of atmospheric pressure. They knew at what
volume, and at what speed, the water had to fall through the troughs in
the aqueducts, to arrive into the heart of the cities and supply the needs
of the growing population.
About 2,200 years ago, a Grecian named Archimedes, developed the
first practical pump. He took a hollow tree trunk, and carved an
internal spiral corkscrew type groove from one end of the trunk to the
other. By lowering one end of the tree trunk into a mountain lake and
rotating the trunk (on its axial centerline), the water flowed upward
through the spiral groove and dropped out of the upper end of the tree
trunk. By positioning the upper end of the tree trunk over a trough of
an aqueduct, the water began flowing down the aqueduct to irrigate
crops, or to supply the city below with fresh water.

In those days, there were no oil refineries, nor bottlers of carbonated
soda, nor sulfuric acid plants. There was only one liquid to consider,
and move in large quantities ... fresh water from the mountains. With
only one liquid under consideration, fresh water, and no sophisticated
instrumentation, they measured the water’s force, or pressure, in terms
of elevation. It is for this reason that today all over the world, pump
manufacturers use the term ‘Head’ measured in meters or feet of
elevation to express pressure or force. The term ‘flow’ expresses volume
over time, such as gallons per minute, or cubic meters per second.

Head versus pressure
__
There’s a language barrier between the pump manufacturers and the
pump users. They use different terminology. Pump users, the operators
and mechanics, use pressure gauges that read in psi, pounds per square

77 w