10/09/2012
If “peristaltic pump” reminds you vaguely of school, it’s because
you might have heard it in a high school biology class. Peristalsis is
the process by which food gets from your mouth to the other end of your
gastro-intestinal tract. A more visible example might be seeing
time-lapse photography of a snake swallowing an object that is wider
than he is.
In peristalsis, whatever is being moved is on the inside of a tube,
and outside forces are squeezing the tube, starting at one end and
moving to the other end. As it is in nature, so it is with a peristaltic
pump.
A peristaltic pump is classified as a positive displacement pump,
and is used to pump fluids. The tube is filled with product, and a
rotor with rollers, “wipers” or “shoes,” turns, causing the rollers to
compress the tube at one end. Just like the biological example we used,
the fluid is forced to the other end and finally out of the tube.
Similar to squeezing a tube of toothpaste.
When the fluid is displaced, it causes a vacuum,
and product is drawn in behind the rollers to refill the tube. This is
often called “resilience” or “restitution.” The cycle starts over again
for as long as there is fluid to pump and the rotor turns.
A popular application for a peristaltic pump is when sanitation is at
a premium. Because neither the rotor nor the rollers touches the inside
of the tube, there is less chance of any outside parts
cross-contaminating the contents of the tube. Medical applications
include pumping IV fluids and circulating blood through a heart-lung
machine during heart bypass surgery.
It is also used for aggressive chemicals and other instances where
the environment needs to be protected from the fluids, or where the
fluid or sludge needs to be protected from the environment. Due to
their design, they are often the first choice for pumping viscous fluids
or abrasives.
This means that there are no pressurised seals or O-rings to worry
about. The only major design concern is that the tubing has to be
elastomeric to maintain the integrity of the circular cross sections
after repeated and prolonged use.
Besides being difficult to contaminate, peristaltic pumps are also extremely low-maintenance, and no backflow or check valve is needed to prevent siphoning.
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