Watson-Marlow 505Du - Manual (Page 4)

4
Recommended operating procedures
DO keep delivery and suction lines as short as possible.
DO use the minimum number of bends in rigid pipe runs. If there must be a bend,
use a swept bend and not a tight elbow.
DO use suction and delivery pipelines with a bore equal to or larger than the
bore of the tube fitted in the pumphead. When pumping viscous fluids, the
losses caused by increased friction can be overcome by using pipe runs with a
cross sectional area several times greater than the pumping element.
DO run at a slow speed when pumping viscous fluids. When using the 501RL
pumphead, a 4.8 or 6.4mm bore tube with a 1.6mm wall will give the best results.
Tube smaller than this will generate a high friction pressure loss, so reducing the
flow. Tube with a larger bore will not have sufficient strength to restitute. Flooded
suction will enhance pumping performance in all cases, particularly for materials
of a viscous nature. Silicone and Marprene tubing is available with a 2.4mm wall
thickness for speeds up to 200rpm. (The rotor will require re-setting to a
roller/track gap of 3.8mm.)
DO use the largest possible bore tube running at slow speed for the longest tube
life.
DO fit an extra length of pump tube in the system so that you can move the tube
through the pumphead occasionally, without needing to break the pumping
circuit. This is particularly useful for extending tube life in long running sterile
applications.
DO keep the track and rollers clean, and ensure that the rollers are free.
DO NOT fit valves in the suction or delivery line without considering that
peristaltic pumps are self priming and will hold their prime up to several metres,
so there may be no need for non-return or foot valves, nor for the loading valves
required on many other kinds of pumps.
Any valves fitted must cause no restriction. If electrically actuated valves are
fitted, they should be interlocked so that the pump will only run when the valves
are open. Fit an automatic by-pass if manual valves are installed.
When using Marprene or Bioprene tubing, after the first 30 minutes of
running, re-tension the tube in the pumphead by releasing the tube clamp on the
delivery side a little and pulling the tube tight. This is to counteract the normal
stretching that occurs with Marprene and Bioprene, which can go unnoticed and
result in reduced tube life.
Tube selection The chemical compatibility list published in the Watson-Marlow
catalogue is only a guide. If in doubt about the compatibility of a tube material
and the duty fluid, request a tube sample card for immersion trials. Remember
the sample will be fully immersed, but the fluid when in use will only be in contact
with the inside of the tube. If the material swells but does not lose its strength it
could be worth considering.
Viscous dispensing To overcome the common problems of reduced accuracy
and dripping delivery pipes, the suction and delivery lines should be kept as
short as possible. Use larger bore transmission tubing than that in the pumphead
to keep the friction losses to a minimum. Improvement will be noticed if rigid or
semi-rigid pipe is used on the delivery side. The rigid tube is effective in
reducing over-run because it does not expand during pumping.