The simple and reliable peristaltic pump is increasingly being chosen
by OEMs in preference to other positive displacement types for a variety
of products, from domestic appliances to industrial process equipment
In the peristaltic pump, the pumped product is enclosed within
continuous, flexible tubing from source to delivery. There is no leakage
path, thanks to the total lack of glands and seals, and precise volumes
of product are displaced by each cyclic squeeze/release action on the
tubing. A well designed pump, featuring sprung roller arms, rigid track
and quality tubing, optimum tube occlusion and recovery, combined with
modern control technology, can deliver sustained accuracy to within
+/-0.5%, regardless of variations in product viscosity and without fluid
back-flow or slip.
Low maintenance is another prime consideration. The pump is essentially
simple, and modern elastomer tube technology ensures long tube life. With
no valves, vanes, lobes or impellers to wear corrode or block, predictive
maintenance is, for all practical purposes, confined largely to periodic
changes of tubing - in itself a quick, simple operation requiring neither
special tools nor a high level of skill.
Design points
Peristaltic pumps are lightweight and compact, compared with most
positive displacement equivalents. Their small footprint is easily
accommodated without compromising the original design, and pumps of this
type are readily adaptable to manufacturers' existing designs. Indeed,
many peristaltic pumps are retrofitted in cases where the original pump
selection has under-performed.The straight through flow path, in
combination with the gentle roll/squeeze pumping action and low running
speeds, enables easily damaged and/or multi-phase media be pumped without
shearing, separation or adverse effect on liquid/solid ratios. Moreover,
the absence of crevices and dead spots, where bacteria and product
residues might otherwise accumulate, enhances the hygienic integrity of
the system.
Application areas
Hygienic operation, accuracy and the ability to handle delicate products
have made the food, dairy and allied industries prime sectors for
peristaltic pumps. Many thousands are fitted in vending machines
dispensing fruit juices, milk, wine, hot water and so on, as well as in
kitchens handling detergent and rinse aids in dishwashers.
Dispensing and scavenging printing inks, varnishes and coatings are
common duties in the printing industry. On flexographic printing
machinery, for example, peristaltic pumps re-circulate ink from a
container, through an ink duct and back to the container in a continuous,
8 - 16 hour/day, operation. At the end of a shift or when changing
colours, the tubing is simply replaced in a matter of minutes and cleaned
later.
In one application, water based paint is dispensed for the automatic
printing, two at a time, of logos on to stacks of wooden pallets. Twelve
print heads mounted on four independent carriages - two on each side -
are each provided with a paint bath fed by a peristaltic pump. These are
individually set for the required flow rate and controlled by a master
PLC. The paint is highly viscous and frequently contains solid lumps,
which caused problems for centrifugal, piston and diaphragm pumps
originally tried for the duty.
Continuous development in elastomers, methods of tube occlusion and
control technology are likely to result in even wider adoption of the
peristaltic concept, not only by OEMs but across the whole spectrum of
industry. Further information on the subject can be obtained from
Watson-Marlow Bredel, whose range of peristaltic pumps provides outputs
from microlitres to 80 m3/h and pressures up to 16 bar.