Pumps require various components for proper operation and safety. Strainer filters are installed on the suction side to prevent debris from fouling pumps. Isolating valves on the suction and discharge sides allow pumps to be safely isolated for maintenance. Positive displacement pumps always require a relief valve on the discharge side to prevent over-pressurization if the discharge is shut, while centrifugal pumps may require a priming pump to remove air if using a negative suction lift. Fire pumps on ships must have non-return valves if centrifugal and a relief valve is essential for positive displacement fire pumps to regulate pressure.

1. Pumps(ingeneral):
 When2 pumpsare fittedinparallel andwhere one alwaysneedstobe keptreadyasstandby,
it isnecessarytofitnor-returnvalvesonthe discharge side of the pumptopreventbackflow.
 Strainerfiltersare fittedonthe suction side of all pumpstopreventsolidmatterordebrisfrom
foulingthe pump.
 Dependingonusage,low&highpressure alarmsare fittedtomonitorthe operationof the
pump.
 Isolatingvalvesare tobe fittedonthe suctionanddischarge side of the pumpto allow forsafe
isolationof the pumpwhenitrequirestobe takenoutof service andfor maintenance.
 Airpurgingcocks are fitted.
 Pressure gauges forthe pump& ammetersforthe motor are necessarytomonitorthe
performance of the pump.
Solid displacement pumps:
 A full flow relief valve isalwaysfitted atthe discharge side of these pumpstopreventdamage
due to increasingpressure inthe pumpedif the dischargeside valvesshouldbe inadvertently
fullyorpartiallyshut.Normallybypassedtothe suctionside of the pump.
 A positive displacementpumpmustnotbe operatedagainstaclosedvalve onthe discharge side
of the pump,because ithasno shut-off headlike centrifugal pumps.A positive displacement
pump operatingagainsta closeddischarge valve will continue toproduce flow andthe pressure
inthe discharge line will increase,until the lineburstsorthe pumpis severelydamaged,orboth.
 A relief orsafetyvalve onthe discharge side of the positive displacementpumpistherefore
necessary.The relief valve canbe internal orexternal.The pumpmanufacturernormallyhasthe
optiontosupplyinternal relief orsafetyvalves.The internalvalve shouldingeneralonlybe used
as a safetyprecaution,anexternal reliefvalve installedinthe discharge line withareturnline
back to the suctionline orsupplytankisrecommended.
 Plungerpumps - a reciprocatingplungerpushesthe fluidthroughone ortwoopenvalves, closed
by suctiononthe way back.
 In case of reciprocatingpumps,anairbottle I fittedonthe discharge line toactas a pressure
pulse damper. Asthe discharge pressure risesthe airiscompressedinthe vessel,andasthe
pressure fallsthe airexpands.The peakpressure energyisthusstoredinthe airand returnedto
the systemwhenpressure falls.Airvesselsare notfittedonthe reciprocatingboilerfeedpumps
since theymayintroduce airintothe de-aeratedwater.
Centrifugal pumps:
 The pump isnot self primingandhence aprimingpumpisrequiredtobe fittedtoremove the
air fromthe suctionside of the pump casing whenthere isa negative suctionlift.
Oil pumps & their system:
 Fuel oil & LubOil pumpsare usuallysoliddisplacement pumps

2. Problems with centrifugal pumps pumps:
If a motor-drivencentrifugal pump DRAWS TOO MUCH POWER, the trouble will probablybe
indicatedbyoverheatingof the motor.The basiccausesmay be
(1) operationof the pumpto excesscapacityandinsufficientdischarge pressure;
(2) toohighviscosityorspecificgravityof the liquidbeingpumped;or
(3) misalignment,abentshaft,excessivelytightstuffingbox packing,wornwearingrings,or
othermechanical defects.
 AC Motors are ignition protected with built-in thermal overload protection.
Fire pumps
Two independentlypoweredpumpsmustbe providedinall cargoshipsof 1000 tons grossand
overand inpassengershipsof lessthan4000 tons gross.Larger passengervesselsand
passengerferriesmusthave three suchpumps. The pumpsare fittedwithnon-returnvalvesif
theyare of the centrifugal type,topreventlossof waterbackthroughopenvalveswhennot
running.
A relief valveisnecessaryinthe systemif the pumpsare capable of raisingthe pipeline pressure
so that itis greaterthanthe designfigure.Withcentrifugalpumpsthe relief valve isunlikelyto
be neededbutitisessential forapositive displacementfire pump.Minimumline pressuresand
capacitiesare governedbythe regulations.