Membrane Filter Elements
40 Operating Manual Status: 06/2001/01
6.4.1 Simple wash (Gap wash)
Figure 6-7
Gap-wash process
6.4.2 Thorough wash
Figure 6-8
Standard cake wash
With the simple wash, following the suspension, wash
medium is pressed through the suspension canal into
the filter chambers.
An important point to pay attention to is that the filter
cakes have not yet grown together; i.e., a gap remains
in the centre of the chambers.
From the gap the wash medium then flows through the
filter cakes.
Make sure that the pressure remains constant during
the transition from filtration to cake washing. If the
pressure drops, the filter cakes can fall together. In this
event, a positive result cannot be achieved in cake
washing.
Note
The permissible washing pressure is dependent on the operating temperature and the
filter element design (see Graphs 11 and 12 in the Appendix of this Operating Manual,
Page 62).
With thorough wash, the washing medium flows through
the wash plate (blue marking/three dots) on one side of
the filter chambers and is then pressed through the filter
cake within the entire chamber.
The washing filtrate is then collected in the pressure
plate (red marking/one dot) and discharged.
Fluid routing can also take place in the opposite
direction.
Optimum washing results are achieved if the
membranes are charged with squeezing pressure
during cake washing to stabilise the filter cakes. The
effect of the membranes is not given until the
membrane squeezing pressure is slightly higher than
the washing pressure.
e.g. Membrane squeeze = 4.3 bar
Wash water pressure = 4.0 bar
