Spirax Sarco BSK1 - Page 11

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11
Inlet over the plug
(DN150,DN200e250
withbalancingdisc)
Inlet below the plug
(DN15÷150)
Fig. 2
Note: Thebalancingdiscisatwo-stageinternalby-passdevice(Fig.3)whichsignicantlyreduces
themotionforceofthehandwheelintheeventofhighdi󰀨erentialpressures.Whentherststage
opens,itactsasapre-openingpilotplugandallowsacontrolledowofuidtopass.Thisgradually
reducesthedi󰀨erentialpressurepresentbetweenupstreamanddownstreamthevalveand,asa
result,reducestheforcerequiredtoliftthesecondstage(mainplug)fromitsseat.Typically,large
on/o󰀨valvesaresubjectedtohighdi󰀨erentialpressuresevenundernormaloperatingconditions.
Therefore, the closure of these valves would be almost impossible without the balancing disc.
Fig. 3
2°
stage
1°
stage
These valves are not designed to withstand severe stress, so the mounting pipelines should be
suitablymounted,alignedandproperlysupportedinordernottotransmitanyadversee󰀨ectsof
expansion(thrust,torsionandexing movements may causeleakages,deformationandand/or
non-allowablestresstovalvebodies).Inaddition,allcouplingandsealingcomponentsshouldbe
constructedwithmaterialsthatareallowableandcompatiblewiththesystemspecications.During
valveassembly,angesshouldbeperfectlyalignedandgasketsperfectlycentred,carefullycleaned
and should not present any signs of damage, in order to ensure perfect tightness. Evenly cross-
tightenthebolts,respectingrecommendedtighteningtorques(Asshowninthetableonpag.10)to
avoid over-tightening which might produce further stress over the whole structure.
Note:valvesandpipelinesworkingwithhigh(>50°C)orverylowtemperatures(<0°C)should
beinsulatedbysuitableinsulatingjacketsinordertopreventdirectcontactwithpersonnel.Ifthis
isnotpossible,providesuitablewarningsignboardsinproximityoftheunits/pipingthatrepresent
hazardousconditions.Ifitisnecessarytoinsulatethevalves,makesurenottocompromisetheir
correctoperation.Thegasketbetweencoverandstu󰀩ngboxmustalwaysremainperfectlyvisi-
ble and accessible. During welding, coating and/or brickwork operations, valve should always be
suitably protected from welding residue or drops as well as from dust, sand/grit or other building
materials. Moreover, screws, spindle and all plastic parts should never be painted to avoid their
possible malfunction.
Insteamplants,itisalwaysadvisabletoinstallathermodynamicoraoatingcondensatesteamtrap
upstream of the isolation valves, to ensure the adequate condensate drainage in order to protect
valves,equipment,downstreaminstrumentsandpipingfromdamagesduetowaterhammere󰀨ects.
To remove any foreign bodies or impurities that may damage the gaskets surfaces, before com-
missioningthesystemallpipelinesshouldbethoroughlywashedandushedwithcompressedair,
with valves in fully open position.