Page 18 - Chemical Technology

16 Chemical Technology • January 2013
pumps, valves and actuators
By design, the peristaltic pump is ideal for the de-
pendable handling of abrasive, corrosive, viscous,
high density and high solid content fluids. It thrives
in those applications where other types of pump fail. Water
and waste water industries, mining and chemical process-
ing are all prime markets for this workhorse. But being
equal to the tough demands of these applications is far
from its only strength. The peristaltic pump can also be
extremely versatile.
Different hose and tube options allow this pump to
handle an exceptionally wide range of fluids; there’s also a
huge choice of flow rates and pressures to suit almost every
application. And perhaps somewhat overshadowed by its
dominance in heavy-duty slurry and sludge handling, is the
peristaltic pump’s eminent suitability for handling shear
sensitive products. It has a smooth, squeezing action that
makes it ideal for use with flocculants, sensitive polymers
and fragile cell cultures.
The growing awareness of the peristaltic pump’s wider
potential is leading to its increased use in less arduous
fields of application. It is regularly specified by the printing
and packaging industries in place of air diaphragm pumps
as it is gentle on the product but still able, for example, to
handle viscous metallic inks. The food, drink and pharma-
ceutical industries are also regularly installing this type of
pump. This is because the pumped product is isolated from
the workings, there’s no danger of contamination and it’s
easy to sterilize.
Another key factor in the rising popularity of the peristal-
tic pump is its fit-and-forget quality. Its lack of valves, seals
and glands makes it inexpensive to maintain. Indeed the
only replacement part on a peristaltic pump is the hose
or tube, a relatively low cost item that is easily exchanged.
These are important qualities as companies strive to opti-
mize production processes and minimize costly downtime.
Design basics
In order to expand on why a peristaltic pump is the best
choice for a wide spectrum of applications, we first need
to consider the design principles. Key to its success is the
fact that the medium being pumped is completely con-
tained within a reinforced hose. A rotating shoe or roller
passes along the length of the hose creating a total seal
between the suction and discharge sides of the pump.
As the pump’s rotor turns, this sealing pressure moves
along the hose forcing the product to move from the pump
Peristaltic
pumps -
A lot more than just
heavy duty
Verderflex ® industrial peristaltic
pumps are extremely robust,
ideal for heavy duty operations on
continuous or intermittent duty
cycles. They are a simple to use,
easy to control, versatile and a
reliable way to pump liquids.
and into the discharge line. When the pressure has been
released, the hose recovers, creating a vacuum which
draws the product into the suction side of the pump, the
priming mechanism. Combining these suction and dis-
charge actions results in a self-priming positive displace-
ment pump.
The advantages of this design are numerous. The perfect
seal between the two sides of the pump means that there is
no product slip. In addition, when coupled with the pump’s
linear speed-flow characteristic, it makes the peristaltic
pump ideal for dosing. Additionally, as the pumped liquid
is totally contained within the hose or tube, the design is of
considerable benefit to hygiene conscious applications. The
total containment of the fluid has the added advantage that
no moving parts can clog or react with chemically aggres-
sive fluids.
High tech hoses
Developments in tube and hose technology have a signifi-
cant role in the peristaltic pump’s wide application scope
and high reliability. The choice includes resistance to high
temperatures, corrosive chemicals, oils, fuels, solvent and
mineral acids and of course includes special grades for
food, drink and pharmaceutical handling tasks
Advances have also been made in the way hoses are manu-
factured. Historically hoses would fail due to early fatigue.
The rubber layers and the reinforcement layer become
dis-bonded, a process that is often accelerated by externally
machining the hose to achieve equal wall thickness. However,
a new hose production process has been developed by some
manufacturers. This ensures a uniform wall thickness without
the need for secondary machining and this significantly
extends the service life of the hose.