614 Pumps, Valves, And Fansa

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


• 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.


• 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 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

614 Pumps, Valves, And Fansa

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