reachthe surfaces. Generally,internal radii of 3 mm (1/8 inch)are recognizedas
adequate to accomplish cleaning. Smaller radii are permitted for smaller
components withinthe valve.In thesecases wheresmallerradiiare required,
theyshouldnot be less than0.8 mm (1/32 inch).The manufacturerof the valve
shouldspecifythe presenceof suchradii.
16.3.7 Process and installation
Whendesigning a processsystem thereare additionalconcernsthat mustbe taken
into consideration.Are therelegalrequirementsof the regulatoryauthority? For
example, pasteurization systems, including bothbatchand continuous systems,
havespecial requirements for the valvesusedto segregatepasteurizedfrom
unpasteurizedproduct. Thismayrequirespecialleakdetectionand rapidres-
ponsetimesfor valve actuation.Aseptic systems require valvesthat can be
demonstratedto be bacteria tight.
Generally, valveswill be designedfor self-closurein the eventof a power
failureduringprocessing. However,theremaybe instanceswhereit is more
beneficial for the valves to remainopenso that the systems can self-drain.
Therefore,caremust be exercisedin the selection of the valves and their
placement withinthe system.
It is quitecommonto use a block and bleed'configurationof valvesto assureseparation of differentstreams (Fig. 16.6).Installers shouldpay extra attention to assurethat the bleedlinesproperly drainand do not retainfluids. The foodindustry wouldbe greatly helped by the availabilityof valvesthat providethe securityof ablockand bleed'systemwhilegreatlysimplifying
draining, avoidingstagnantproduct.Installers mustbe careful not to create a
commoninstallationerrorthat produces a `block±block±bleed' configuration.
Caremustalso be exercisedto assurethat valvescan be easilyaccessedfor
periodic maintenanceand inspection. Valvescommonly includecomponents,
whichwearand requireperiodic replacement.
Fig. 16.6Improvingthe hygienicdesignof valves 271