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INTRODUCTION TO NAVAL ENGINEERING. PUMPS, VALVES, AND FANS. OBJECTIVES. How to control the flow of fluids. How to create flow of fluids in our system. Bernoulli’s Principle. Net Positive Suction Head (NPSH). Fans. VALVES. Globe Valve. Most common valve in a propulsion plant

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PUMPS, VALVES, AND FANS

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Pumps valves and fans

INTRODUCTION TO

NAVAL

ENGINEERING

PUMPS, VALVES, AND FANS


Objectives

OBJECTIVES

  • How to control the flow of fluids.

  • How to create flow of fluids in our system.

    • Bernoulli’s Principle.

    • Net Positive Suction Head (NPSH).

  • Fans.


Valves

VALVES


Globe valve

Globe Valve

  • Most common valve in a propulsion plant

  • Body may be straight, angle, or cross type

  • Valve inlet and outlet openings are designed to suit varying requirements of flow

  • Valve may be operated in the partially open position (throttled)

  • Commonly used in steam, air, oil and water lines


Gate valve

Gate Valve

  • Used for a straight line of flow where minimum restriction is desired

  • Not suitable for throttling

  • May be rising stem or nonrising stem


Ball valve

Ball Valve

  • Most ball valves are quick acting - only require 90o turn to completely open or shut valve

  • Some ball valves may have gearing for ease of use (also increases operating time)

  • Used in seawater, sanitary, trim and drain, air, hydraulic, and oil transfer systems


Butterfly valve

Butterfly Valve

  • Lightweight, relatively small, and quick acting

  • May be used for throttling

  • Used in freshwater, saltwater, lube oil, JP-5, F-76, and chill water systems


Check valve

Check Valve

  • Allows fluid to flow in a system in only one direction

  • May be swing, lift, or ball type

  • Check valves may be built into globe valves or ball valves


Relief valve

Relief Valve

  • Installed in piping systems to protect them from excessive pressure

  • The relieving pressure is set by the force exerted on the disk by the spring

  • Relief valves may have a lever which allows manual opening of the valve for test purposes


Valve operating devices

Valve Operating Devices

  • Manual

    • Handwheel or lever is directly connected to the stem and is operated by hand

  • Hydraulic

    • Hydraulic pressure is applied to one side of a piston which is connected to the stem of the valve

  • Motor

    • A hydraulic, electric, or air driven motor is used to turn the stem of the valve

  • Solenoid

    • Uses an electromagnet to open or close a valve against spring pressure


Pumps

PUMPS


Pump components

Pump Components

DRIVE TYPE

(electric motor,

steam drive, gear

driven, etc…)

IMPELLER

PUMP SHAFT

DISCHARGE

CASING

SUCTION


Pressure head

Pressure Head

  • Head

    • The vertical distance between two horizontal levels in a liquid

    • A measure of the pressure exerted by a column or body of liquid because of the weight of the liquid

  • Since a pump may be installed above, at, or below the surface of the source of supply, the pump must be able to overcome the net static head in order to pump from one elevation to another

  • Equal to Z + P/


Pressure head1

Pressure Head

NET STATIC

HEAD

STATIC

DISCHARGE

HEAD

STATIC SUCTION

PRESSURE

PUMP


Velocity head

Velocity Head

  • Head required to impart velocity to a liquid

  • Equivalent to the vertical distance through which the liquid would have to fall to acquire the same velocity

  • Equal to V2 / 2g


Friction head

Friction Head

  • The force or pressure required to overcome friction is obtained at the expense of the static pressure head

  • Unlike velocity head, friction head cannot be “recovered” or reconverted to static pressure head

  • Thermal energy is usually wasted, therefore resulting in a head loss from the system


Bernoulli s theorem

BERNOULLI’S THEOREM

  • The Bernoulli equation is a special statement of the general energy equation

  • Work added to the system is referred to as pump head (hP), while losses from the system are referred to as head loss (hL)


Bernoulli s equation

Bernoulli’s Equation

Z1 + (P1/) + (V12/2g) = Z2 + (P2/) + (V22/2g) + hP - hL

Where:

Z : Elevation (ft)

P : Pressure (lb/ft2)

 : Density (lb/ft3)

V : Velocity (ft/sec)

g : acceleration

(32.2 ft/sec2)

Hp: pump head (ft)

HL: Head Loss (ft)

= f(L/D)(V2/2Zg)

where

f : friction factor

L: Length

D: Diameter


Positive displacement pump

POSITIVE DISPLACEMENT PUMP

  • Fixed Volume

  • Volumetric Flow rate is proportional to speed

  • A relief valve will always be on the discharge end of the pump


Pumps valves and fans

EXAMPLES


Reciprocating pump characteristic curve

Reciprocating Pump Characteristic Curve

N2 = 2 N1

N1

N2

hP (ft)

.

V (gpm)


Non positive displacement pumps

NON-POSITIVE DISPLACEMENT PUMPS


Pump laws

Pump Laws

Apply to centrifugal (non-positive displacement)

pumps only

V  N

Hp  N2

W  N3

V = volumetric flow rate

N = speed of rotation

Hp = pump head

W = power required (prime mover)

.

.

.


Pumps1

PUMPS

  • Centrifugal:

    • Parallel pumps:

V2 = 2V1

2 pumps

HP

HP2 = HP1

1 pump

GPM

V


Pumps2

PUMPS

  • Series (called staging):

2 pumps

HP2 = 2HP1

HP

V2 = V1

1 pump

GPM

V


Net positive suction head

NET POSITIVE SUCTION HEAD

  • Net Positive Suction Head: that pressure required at the suction of a pump to prevent cavitation.

    • cavitation: the formation of bubbles due to area where P < PSAT, and the subsequent collapse upon migration to a high-press. area.

      • causes noise and damage due to erosion and fatigue failure.


Net positive suction head1

NET POSITIVE SUCTION HEAD

  • Need enough pressure on the suction side so that P < Psat. If P < Psat, water flashes to vapor causing damage to the pump.

pump


Pumps valves and fans

FANS


Pumps valves and fans

Fans

  • Operate on the same principle as non-positive displacement pumps: impart a velocity to a fluid and convert this kinetic energy into a pressure by the use of a diffusing chamber

  • Two types

    • Centrifugal: similar to a pump impeller, used in refrigeration compressors or gas turbine compressors in small gas turbine engines

    • Axial: similar to a propeller, used in forced-draft blowers


Bernoulli s theorem1

BERNOULLI’S THEOREM

Z1 + P1/D + 1/2(V12/g) =Z2 +P2/D + 1/2(V22/g) + gc/g(wk) + HL

Where:

Z : Elevation (ft)

P : Pressure (lbs/ft2)

D : Density (lb/ft3)

V : Velocity (ft/sec)

g : acceleration

(32.2 ft/sec2)

wk: work (ft-lbs)

HL: Head Loss

= f(L/D)(V2/2Zg)

where

f : friction factor

L: Length

D: Diameter


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