Watson-Marlow 520Du - Manual (Page 7)

Watson-Marlow 520Du User Manual 7
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, eliminating 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,
creating a partial vacuum which is filled by fluid drawn from the inlet port.
Before the roller reaches the end of the track, a second roller compresses the tube
at the start of the track, isolating a packet of fluid between the compression 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.
Animal digestive tracts function in a similar way.
Suitable applications
Peristaltic pumping is ideal for most fluids, including viscous, shear-sensitive, corro-
sive and abrasive fluids, and those containing suspended solids. They are especial-
ly useful for pumping operations where hygiene is important.
Peristaltic pumps operate on the positive displacement principle. They are particu-
larly suitable for metering, dosing and dispensing applications. Pumps are easy to
install, simple to operate and inexpensive to maintain.