∑ Rotaryvalve: also knowas a rotary airlockvalve or a star valve,this consists
of a multi-chamberedshaftthat rotateswithina cylindrical housing.The
valves are particularlyefficientfor transferring product betweenzonesof
differing pressureor vacuum.Somemanufacturershavedesignedmodels
specificallyto meetthe requirementsfor mechanicalcleaning.
16.2.3 Valvesusedin dry productprocessingsystems
∑ Iris valve: an iris valve featuresa fabricor multi-section metaldiaphragmthat
opensor closesby a twisting motion of the valve's outerhousing similar to
the actionof a camera iris.
∑ Inflatableseal ductvalve: these valves use a rubber bladderattachedto the
outer circumferenceof a valve disk.Afterthe valveis rotatedinto the closed
position,the bladder is inflatedto obtaina seal withthe duct'sinterior.
∑ Flip-flopvalve: a flip-flopvalvehas two movable valvedisks or flaps,
located one abovethe other,whichcyclealternativelyby mechanicalmeans.
Product is passedinto the intermediate chamber between the two valvedisks
before passingthroughthe valve body.Likerotaryvalves, flip-flopvalves
can transferproduct between zonesof differingpressureor vacuum.
∑ Diverter valve: as its nameimplies, a diverter valveconsistsof two or more
ports intowhichthe productstreammay be directed.Depending on the
number of discharge portsprovided,the actuating mechanism maybe a
simple flap valve,a positioningslidevalve, or a rotaryport plate.
16.3 Hygienic aspectsof valvedesign
The ubiquitousnature of valves withinprocessing systemsplaces themin a
positionto potentially havean impacton every particleof product passing
throughthe system.Valvescan be smallor verylarge;simpleor verycomplex
in design.Therefore,theirhygienic designis vitalto producinga high-quality,
safe product.
Valvedesign plays a majorrole in whetheror not a particular valveor design
is suitable for its intended application. Valves that are intended to be
mechanicallycleanedor cleaned-in-place (CIP)requirespecialdesignfeatures.
The designand operation duringcleaningmust assure thatall components
potentially contacted by product will also be contacted by cleaning and
sanitizingfluids(includinghot waterand steam)withsufficientturbulence or
flow to thoroughlyclean and decontaminatetheseareas.Generallyspeaking,
any manually operated valve,regardlessof its type or design,and valves usedin
dry product processing systems should not be considered as suitable for
mechanicalcleaning methods. The inability for automatic cycling of the valve
during cleaningprevents cleaningand sanitizing solutionsfromreachingall
areas of the valve seats and other seals.Thesevalvesare onlysuitable for
disassemblyand manual cleaning.
268 Handbookof hygiene controlin the foodindustry