18.2.2 Mechanical seals
Mechanical seals have replaced the stuffing boxused so far in the food
technology.The design of the mechanicalseals should providethat the pressing
springfor the sliding ringlocatedin the product chamber is encapsulated.
Exposedthreads(headless screws) or similar should not be located in the
product chamber. Garterspringsare not permitted on the productsideof the
seal.
For normal applicationin breweries and dairiessingle-acting mechanical
sealsare used,often in hard/softpairings (ceramic/carbon). For abrasive media
hard/hardpairings are the betterchoice. For products that crystalliseout or paste,
quenched mechanicalsealsare used(mechanical seal and radialshaftseal with
flushing).For toxicproducts or in pharmaceuticalapplicationsdouble-acting
mechanicalsealsare usedwithpressurised sealing water.
The construction of the shaftand the arrangement of the mechanicalseal
chamber and lantern should allow for the installationof customer-specific
mechanicalsealsor retrofittingof othermechanical sealsfor the adaptation to
changed media.
18.2.3 Leakagedetection
A lantern should be installed between the pumphousing and the drivingmotor.
Apart fromthe geometricconnection function betweenthe housingand the
motor flange,the lantern is usedto connect the pumpsafelywiththe motor,in
orderto make leakagevisiblein caseof damage. In caseof leakage,productor
cleaningsolutionmust not be allowedto enter the shaft area of the motor where
microorganismscould growunnoticed. Thepenetrationof leakagefluidsor
splash waterfromthe lanternport into the shaftarea of the motor duringoutside
cleaningcan be avoidedeffectivelyby providing a splash ring on the shaft and a
labyrinthseal between the shaft and the lantern housing.
18.2.4 Fillingand drainage of the pumphousing
For an optimal start of a self-primingpump, the dischargesocket shouldbe
arrangedin a waythat air can evacuate autonomouslyat any operatingpoint
(Fig. 18.4b). In this casea radialupwards directeddischarge socket is most
suitable. Withthis arrangement, suctionand discharge sockets are located on the
same axis,whichsimplifies pipingand plant layout.
Non-aqueousproducts and mainly pharmaceutical applicationsrequirethe
drainage of rinsing waterfromthe pump housing. TheEuropean Hygienic
Engineeringand Design Group (EHEDG)stipulates this as an optionfor pumps.
Drainagevalves usedin this casemustbe withoutdeadendsto ensurethat the
production processis not endangered (Figs18.4e and 18.4f).
282 Handbookof hygiene controlin the foodindustry