the inletis closed but the outletis still open,when a biggerheight of fall exists
and the mediumhas alreadyreacheda higher temperature(water of 20 ÎC will
evaporate in a suspendedliquidcolumn of approximately 10 m). If the cleaning
systemand plant partsto be cleanedare arrangedon differentlevels, appropriate
measures must be takento prevent the suspensionof liquidcolumns,for instance
by usingoverflow valvesin descending pipes.
In-linedosing
In-linedosingsystemsmustbe equippedwithdosingpumpsthat haveadjustable
strokevolumeand strokefrequencyto ensureoptimaldistributionof cleaning
solutionsin the flow.The distributionof cleaningsolutionin the flowbecomes
morehomogeneousif the requiredvolumeis distributedthroughoutthe cleaning
cyclein a largenumberof smalldosesratherthan a smallernumberof largedoses.
Largerdosescan resultin wave-likeaccumulationsof high and low concentrations.
Double-seatvalves
Duringcleaning,the valvedisksin the double-seatvalves installed in the system
mustbe lifted so that they are cleanedproperly.Alternatively,the systemshould
be cleanedby loopingso that the valvescan openfullyand the valve seatsbe
cleanedfrombelow.Seatliftingshouldoccurperiodicallyduringeachcleaning
phase. The duration of the liftingpulsesand the intervals betweenthemdepend
on the levelof soiling, and are generally between 10 and 60 secondsin duration,
with3±5 minutes between pulses. To minimize the consumption of cleaning
agents,Varivent double-seatvalvesare equippedwiththe LEFFmodule.^2 Using
the LEFFfunction, the detergent rate can be reducedto a minimumduringthe
liftingprocedure,whilethe cleaning effect remains unchanged.
The maximum number of double-seatvalvesthat can be combined in one
liftinggroupis five.If too many valvesare lifted at the sametime,the pressure
in the downstreampipeand valvesystemdrops.The lifting function always
requires pressureof at least1 bar aboveatmosphericpressure, otherwise the
valveseat will not be cleanedand air will be drawninto the systeminstead. This
mustbe takeninto account when designingvalve systemswhereseat-lifting will
be required for cleaning,particularlyin the caseof tankreturn.
Flushingout withmainswatershouldneverbe timecontrolled. The flushing
out mediummustalwaysbe at constantpressureand in practicethis is neverthe
casewithmainswatersupplies. Therefore controllingflushingout by timing
wouldresultin varying volumesof waterbeingintroduced into the system.
Flushing out should be controlled via volume measurements, or direct
measurementof a parameter suchas conductivityor pH value.
27.5 Future trends
Hygienic designand certificationare importantelements in the improvement of
CIP systems,and will be usedto develop improved components,processmodels
Improving cleaning-in-place (CIP) 443