As withotherequipment, hygienicdesign is basedon suchfeatures as:∑ materials of construction;
∑ internalsurface texture;
∑ accessibilityfor cleaning and inspection(includingleakdetectionand seat
lifting);
∑ draining;
∑ elimination of cracks,crevices,and niches;
∑ internalangles and corners;
∑ processand installation concerns.
16.3.1 Materialsof construction
Traditionally, hygienic valves for the foodindustry havebeenfabricatedin
stainlesssteel.The AmericanIron and Steel Institute, AISIseries300 stainless
steelsand theirequivalent cast grades,havebeenthe materials of choicefor the
metallic componentsof the valves. Non-metallic componentsfor seals,valve
seats,diaphragms, plunger, and plugencapsulationsare to be acceptable to the
convening regulatory authorityand be non-toxic,relativelyinert, non-porous,
non-absorbent, and compatiblewiththe environment of intendeduse, cleaning,
and sanitization. Caremust be exercised to assurethatproper non-metallic
materials are selected; with particular emphasis on the fat content and
temperature ranges of the products intended to be processed.
16.3.2 Internal surface texture
Product contact surface finishes at least as smooth as an Ra of 0.8m
(32.0inch)on stainlesssteelfreeof imperfectionssuchas pits,folds,and
crevices in the finalfabricated formwill cleansatisfactorily and are recognized
by most hygienic equipment standards. Any deviations rougher than this
minimumshouldbe part of the manufacturer'sspecificationsso that the buyer
can make an informeddecisionto use the valve.
16.3.3 Accessibilityfor cleaningand inspection
Thenormalcycling of valvesduringprocessingand cleaningsubjectvalve
components to highstressand wearof movable components. In largefluid lines,
thesestresses can force productpasssealsor removablevalveseats.Valvesin
dry product processesmaybe subjectedto materials that are quiteabrasive.
Therefore,it is vitalthat valves be both accessiblewheninstalledin a processing
systemand easyto disassembleso that the wearand cleanliness of components
can be periodicallyinspected.Valvesthat are supplied withautomaticpower
actuators generallyare required to have at leasta 25 mm (1.0 inch)space
between the actuator and the valveshaftseal that is opento atmosphere so that a
failureof the sealsis readily observable.
Valvessuchas diaphragmor pinch valves that haveinternal components
subjectto failure,requirea drainopeningto atmosphereto signal component
Improvingthe hygienicdesignof valves 269