Page 21 - Chemical Technology

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Chemical Technology • January 2013
Sub-zero drinks dispensing
The vending machine industry is an established user
of peristaltic tube pumps but an installation in sub-zero
temperatures demonstrates the benefits of the design
particularly well.
In cold climates chocolate syrup used by a vending
machine to make a cup of hot chocolate becomes highly
viscous. So, to deliver the correct measure, in hygienic
conditions and at a consistent flow rate, the OEM chose
a bespoke peristaltic tube pump. In this case a dovetail
section silicone tube was specified that is suitable for
high temperature fluids.
Peristaltic tube pumps with high suction capability are
readily available. Standard models will lift a liquid, such
as water, by as much as 8,5m. However, for this vending
machine application even greater suction was required.
This was achieved without altering the flow rate by fitting
a modified autoclavable cartridge to the pump.
How does a peristaltic pump operate?
Peristaltic pumps work using the process of peristalsis to pump products
through a hose, in the same way that blood, food and oxygen are pumped
around the body.
The hose sits around a rotor which, when turning, compresses a seg-
ment of the hose almost flat.
This compression is released as the rotor moves around the hose with
the hose reinforcements causing it to spring back to its round shape, thus
creating a partial vacuum refilling the hose.
This compression creates a seal and, as the rotor turns, any product
on the discharge side of the rotor is propelled forward and displaced
from the pump.
Combining this suction and discharge action results in a self-priming
positive displacement pump.
Why choose a peristaltic pump?
• Seal-less design The main feature of the peristaltic pump is the tube/
hose. Because this is the only part of the pump to come in contact with
the product, it means the pump avoids corrosion and is leak-free.
• Dry running Many pump users face difficulties when the pump runs dry.
peristaltic pumps are able to do this without any lubrication from outside.
• Self-priming The pumps are capable of self-priming and can handle
products that are likely to 'air' or 'gas'.
• Gentle pumping action In addition, because of the tube/hose and the
pumps’ gentle action, the product being pumped is not damaged in the
process thus making peristaltic pumps ideal for shear sensitive products.
• High suction lift The pumps also have high suction capabilities and
can provide high discharge pressures meaning they are suitable for use
where the product being pumped needs to be moved away from the
area of the pump.
• Reversible Due to the action of the pump it can be used to empty lines
or clear blockages by reversible rotation.
• Non-slip pumping The pumps have no internal backflow giving accu-
rate dosing without slip
• Accurate dosing The pumps are accurate in dosing, with repeatability
of circa ±0,5% and metering capabilities of circa ±2%.
• Enhanced hose life Abrasion resistant Tube/Hose life is not related to
a product’s abrasive qualities. The tube/hose only fails due to fatigue or
chemical action.
• Low life cycle costs When the tube/hose does need replacing the cost
is minimal compared to other pumps’ maintenance costs. In addi-
tion the time needed to replace the tube/hose is much less then that
needed to repair other pump types.
In summary, although the attributes of the peristaltic
pump make it the prime candidate for heavy duty ap-
plications, it brings other benefits that greatly extend its
scope. Its combination of seal-less design, low mainte-
nance, gentle pumping action, high suction life, abrasion
resistance, reversible operation and ability to run dry
gives this technology the edge for a multitude of tasks.
pumps, valves and actuators