Watson-Marlow 120U/D1 - Manual (Page 6)

Watson-Marlow 120 IP31 pumps: general information 4
1.6 Peristaltic pumps -
an overview
Peristaltic pumps are the simplest possible pump,
with no valves, seals or glands to clog or corrode.
The fluid contacts only the bore of a tube, eliminat-
ing the risk of the pump contaminating the fluid, or
the fluid contaminating the pump. Peristaltic pumps
can operate dry without risk.
How they work
A compressible tube is squeezed between a roller
and a track on an arc of a circle, creating a seal at
the point of contact. As the roller advances along
the tube, the seal also advances. After the roller has
passed, the tube returns to its original shape, cre-
ating a partial vacuum which is filled by fluid drawn
from the inlet port.
Before the roller reaches the end of the track, a sec-
ond roller compresses the tube at the start of the
track, isolating a packet of fluid between the com-
pression points. As the first roller leaves the track,
the second continues to advance, expelling the
packet of fluid through the pump’s discharge port.
At the same time, a new partial vacuum is created
behind the second roller into which more fluid is
drawn from the inlet port.
Backflow and siphoning do not occur, and the pump
effectively seals the tube when it is inactive. No
valves are needed.
The principle may be demonstrated by squeezing a
soft tube between thumb and finger and sliding it
along: fluid is expelled from one end of the tube
while more is drawn in at the other.
Suitable applications
Peristaltic pumping is ideal for most fluids, including
viscous, shear-sensitive, corrosive and abrasive flu-
ids, and those containing suspended solids. They
are especially useful for pumping operations where
hygiene is important.
Peristaltic pumps operate on the positive displace-
ment principle. They are particularly suitable for
metering, dosing and dispensing applications.
Pumps are easy to install, simple to operate and
inexpensive to maintain.