Home' Smart Farmer : September 2009 Contents SEPTEMBER, 2009
BY DAVID EAST
WITH wintry conditions following
widespread rains, it may seem
the wrong time of the year to
be writing about choosing the right
pump for an intended job.
The fact of the matter is, it is the right
time to be thinking about summer water
needs and how to pump it.
With the vast expansion of irrigated
agriculture, intensive livestock and
improved home and living conditions,
water has suddenly become one of every
landholder's most valuable assets.
The old windmill and the muddy dam
are really not adequate to fill the water
needs on most properties today.
The new heart of most farm water
systems is the pump, whether it is for
household or livestock needs or
There is also a drive by manufacturers
to develop pumps of superior design and
Landholders buying a new pump are
confronted with a vast array of options
for managing their water systems.
Before buying a new pump it makes a
lot of sense to thoroughly check out
what is available, how it works and that
it is suitable (the right type and capacity)
for the job planned.
There are two broad groups of pump
types: the positive displacement type of
pump and the rotary dynamic type, and
within these two categories, there are
many different designs.
Examples of the positive displacement
pumps are the reciprocating types -- the
bucket, plunger, piston, ram and
diaphragm pumps -- plus a few others
which can be classified as less common
including the swinging vane, screw, semi-
rotary and gear types.
These pumps must discharge against
whatever pressure prevails in the system
-- thus the title positive -- and they draw
the water in, hold it, then push it out in
cycles -- the other aspect of the name,
A positive displacement pump must
put out as much water as it takes in -- the
flow cannot be restricted by valves etc,
without damaging either the pump
and/or its drive.
With these pumps, the quantity of
water pumped is directly proportional to
pump speed and their efficiency is
generally rated around the 50 per cent
mark, regardless of the flow capacity.
It is fair to say that in recent years the
popularity of positive displacement
pumps has been overtaken by the more
flexible centrifugal types of pumps, but
they (positive displacement pumps) are
still most useful for low volume -- high
head operations -- 20 litres a minute at
45 metres head.
Much more common are pumps which
work by spinning the water at high
speed to create the pumping pressure.
These are known as rotary dynamic or
pressure raising pumps and include spur
gear units (used on many crop spraying
machines and in many tractor hydraulics)
as well as axial flow or impeller types
and the universal centrifugal pump.
Modern pumps best
for multiple tasks
For general work on the land today, it is
the centrifugal that comes to the fore.
With centrifugal pumps, mechanical
energy from the impeller propels the
water at increasing speed as it rotates.
At the outer edge of the impeller --
where the water hits maximum speed --
pressure builds up and forces the water
through the outlet.
This system has several advantages over
standard positive displacement type
Output can be controlled by an outlet
valve without causing any damage.
Multiple use pumps available
Two broad group hypes
Advanced plastics improve efficiency
MULTI-USE: Water is now such a valuable commodity that the farm pump may be used for
firefighting, household use or supplying water from dams for livestock use.
It is fair to say that in recent years the popu-
larity of positive displacement pumps has
been overtaken by the more flexible centrifu-
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