Post on 21-Jul-2016
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Valves, Pumps, Valves, Pumps, and Fansand Fans
ReferencesReferences• INE, Chapter 28, pp. 477-501• PNE,
– Chapter 18, pp. 8-10 - 18-20; – Chapter 19, pp. 19-1 - 19-19
ObjectivesObjectives• Basic construction and application of valves
used in the propulsion plant.• Various methods of valve operation. • Operation and application of the different
pumps found in the propulsion plant.• Operation and application of centrifugal and
axial fans.
ValvesValves
VALVESVALVES
• PURPOSE: to control the amount & direction of fluid flow through the lines of a piping system
Valve Valve ComponentsComponents
• Valve body• Disc• Seat • Bonnet
Valve Valve ComponentsComponents
• Packing• Packing gland/nut• Stem• Wheel/Operating mechanism
VALVESVALVES• there are 2 basic valve types:
– A. Stop valves - used to shut off, or partially shut off (throttle), the flow of fluid. Controlled by movement of the valve stem itself.
– B. Check valves: used to permit flow of fluid in only one direction/controlled by fluid movement
Valve TypesValve Types• Globe valves• Gate valves• Ball valves• Butterfly valves• Needle valves• Swing and Lift Check Valves• Stop Check Valves• Relief Valve
Stop ValvesStop Valves
Check ValvesCheck Valves
Special-Purpose Special-Purpose ValveValve
STOP VALVESSTOP VALVES• GLOBE• GATE• BUTTERFLY• BALL
GLOBE VALVEGLOBE VALVE• used for flow control• ADV: excellent throttling
characteristics• DISADV: large pressure
drop across the valve due to the flow restriction (thus more pumping power is required to move the fluid through the system.)
GATE VALVESGATE VALVES• used in systems where
minimal flow restrictions are necessary
• used as cutout or isolation valves
• ADV: small pressure drop across valve
• DISADV: poor throttling characteristics
BUTTERFLY BUTTERFLY VALVESVALVES
• used as cutout/isolation valves
• ADV: quick-acting low pressure drop across the valve, has adequate throttling characteristics
• DISADV: only used for low press/low temp systems due to force involved in valve operation
BALL VALVEBALL VALVE
• Ball with hole through it rotates in a pipe
• Used for isolation in sanitary and sea water systems
• ADV: Low pressure drop, fast operating, can be throttled
• DISADV: Expensive, heavy, poor throttling
Swing and Lift Swing and Lift Check ValvesCheck Valves• Check Valves
– Allow fluid flow in one direction• Swing check valve
– Disc swings through an arc, • Lift-check valve
– Disc moves up and down
SWING CHECK SWING CHECK • Simple design• Allows flow in one
direction• Can not be used as an
isolation valve
Stop Check Stop Check ValvesValves
• Internals similar to a globe valve• Disc is not attached to the stem• Valve stem - long enough to hold the disc
firmly against the seat• Stem raised - the disc can be opened by
pressure on the inlet side
STOP CHECKSTOP CHECK
• Can be used as an isolation valve as well as a check valve
RELIEF VALVESRELIEF VALVES• special type of valve designed to operate
automatically in a system overpressure condition (a protective feature in most systems)
• most relief valves use an adjustable spring to determine lift pressure. System pressure opposes spring pressure, and when pressure is high enough, the valve will open against spring pressure and port the fluid to another location (typically, overboard for ‘safe’ fluids)
RELIEF VALVESRELIEF VALVES
Valve Operating Valve Operating Devices Devices
• Manual• Hydraulic• Motor (electric and air operated)• Solenoid
PumpsPumps
PUMPSPUMPS• Pumps are mechanical devices used to
cause fluid to flow in a piping system. • Pumps are required in all fluid systems to
make up for losses of usable energy in the system caused by flow and they deliver fluid from a low pressure area to a high pressure area.
CAVITATIONCAVITATION• The work done on a system by a pump is converted
into flow work of the working fluid and is seen as a rise in pressure of the fluid.
• All pumps require a minimum pressure at the pump suction to prevent the formation and collapse of vapor bubbles. These bubbles are caused when saturation conditions exist in the pump, and the these bubbles collapsing and impinging on pump internal components is called cavitation .
TERMS OF TERMS OF INTERESTINTEREST
• Pressure head - The vertical distance between the levels of a liquid. It is a measure of the pressure exerted by a column or body of liquid due to the weight of the liquid. For a liquid to be pumped, this pressure head must be overcome before there will be flow through a system
Pressure HeadPressure HeadPump Below SurfacePump Below SurfaceFrictionFrictionLossLoss
Net StaticNet Static(Discharge)(Discharge)PressurePressureHeadHead
Static Suction Pressure HeadStatic Suction Pressure Head
Total StaticTotal Static(Discharge)(Discharge)PressurePressureHead Head
TotalTotalHeadHeadDifferentialDifferential TotalTotal
OutputOutputHeadHead
TERMS OF TERMS OF INTERESTINTEREST
• Discharge head - The pressure a pump can develop on its discharge. As long as discharge head is greater than system pressure head, there will be flow.
Pressure HeadPressure HeadPump Below SurfacePump Below SurfaceFrictionFrictionLossLoss
Net StaticNet Static(Discharge)(Discharge)PressurePressureHeadHead
Static Suction Pressure HeadStatic Suction Pressure Head
Total StaticTotal Static(Discharge)(Discharge)PressurePressureHead Head
TotalTotalHeadHeadDifferentialDifferential TotalTotal
OutputOutputHeadHead
TERMS OF TERMS OF INTERESTINTEREST
• Suction head - Also called suction lift. The vertical distance between the fluid to be pumped and the pump’s suction position over/within the fluid. It is the pressure head that must be overcome before fluid can flow into the pump’s suction.
NET POSITIVE NET POSITIVE SUCTION HEAD SUCTION HEAD
(NPSH)(NPSH)• NPSH is the measure of the pressure at the
pump suction (eye of the impeller.)• Minimum NPSH is the value of NPSH
required to prevent cavitation.
Pressure HeadPressure HeadPump Below SurfacePump Below SurfaceFrictionFrictionLossLoss
Net StaticNet Static(Discharge)(Discharge)PressurePressureHeadHead
Static Suction Pressure HeadStatic Suction Pressure Head
Total StaticTotal Static(Discharge)(Discharge)PressurePressureHead Head
TotalTotalHeadHeadDifferentialDifferential TotalTotal
OutputOutputHeadHead
Pressure HeadPressure HeadSupply Below PumpSupply Below Pump
FrictionFrictionLossLoss
StaticStatic(Discharge)(Discharge)PressurePressureHeadHead
Static Suction LiftStatic Suction Lift
TotalTotalHeadHeadDifferentialDifferential
NetNetStaticStaticHeadHead
TYPES OF PUMPSTYPES OF PUMPS• POSITIVE DISPLACEMENT PUMP
– Rotary– Reciprocating– Variable Stroke– Screw
• NON-POSITIVE DISPLACEMENT– Centrifugal– Propeller– Jet Pumps– Fans
POSITIVE POSITIVE DISPLACEMENT DISPLACEMENT
PUMPPUMP• A pump designed to pump a fixed volume of
fluid for each stroke or rotation of the pump. • Roughly the same volume of fluid will leave
the pump no matter what pressure the pump is discharging against.
• System flow rate varies only with pump speed. CAPACITY IS PROPORTIONAL TO SPEED!!!
EXAMPLES
Non Positive Non Positive Displacement Displacement
PUMPSPUMPS• Operate on principle of imparting velocity on
fluid then converting this fluid into a pressure• TYPES
– Centrifugal– Propeller (not common)– Jet Pumps
CENTRIFUGAL CENTRIFUGAL PUMPPUMP
• Used to pump large volume of water• Can be placed in multiple stages to increase
discharge pressure• Uses centrifugal force to accelerate fluid• VOLUTE is increasing in area – converts
velocity to pressure• Pumps have numerous uses onboard ships
CENTRIFUGAL PUMPCENTRIFUGAL PUMP
PROPELLER PUMPPROPELLER PUMP• A propeller rotating in a narrow tube-like
casing (sleeve) moves the fluid by pushing it through the tube. Pumping capacity is very large and pumping discharge pressure is very low.
JET PUMPSJET PUMPS• Fluid is moved from one location to another by
entraining it in another fluid moving at a high velocity (activating fluid).
• As the activating fluid leaves a nozzle, its velocity in increased and a low pressure area is formed. The fluid that is to be pumped flows into this low pressure area where it mixes with and is carried along with (entrained) the activating fluid.
JET JET PUMPSPUMPS
FansFans
FANSFANS• Mechanical devices used to move large
volumes of air. • Centrifugal - used in ventilation systems• Axial - used in boiler air feed systems and
as compressors
FANSFANS
QUESTIONSQUESTIONS