ENGINEERING LESSON GUIDE 4

1
INTRODUCTION TO NAVAL ENGINEERING
PUMPS, VALVES, AND FANS
2
OBJECTIVES

• How to control the flow of fluids.
• How to create flow of fluids in our system.
• Bernoullis Principle.
• Net Positive Suction Head (NPSH).
• Fans.

3
VALVES
4
(No Transcript)
5
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

6
(No Transcript)
7
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

8
(No Transcript)
9
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

10
(No Transcript)
11
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

12
(No Transcript)
13
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

14
(No Transcript)
15
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

16
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

17
(No Transcript)
18
(No Transcript)
19
(No Transcript)
20
(No Transcript)
21
PUMPS
22
Pump Components
DRIVE TYPE (electric motor, steam drive,
gear driven, etc)
IMPELLER
PUMP SHAFT
DISCHARGE
CASING
SUCTION
23
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/?

24
Pressure Head
NET STATIC HEAD
STATIC DISCHARGE HEAD
STATIC SUCTION PRESSURE
PUMP
25
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

26
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

27
BERNOULLIS 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)
• Losses from the system are referred to as head
  loss (hL)
• Pressure (lbf/in2) is a form of work
• Strictly Mechanical Energy so we get the
  equation
• P1 PE1 KE1 WK PE2 KE2 WKFRIC P2

28
THE CONCEPT OF HEAD

• The vertical difference between 2 levels of
  liquid
• Use FT to measure the pressure exerted by a body
  of liquid in term of weight
• Head a Pressure a Energy
• Velocity Head
• The distance a liquid would have to fall for a
  given V
• Hv V12/2g
• Friction Head
• Hl f(L/D)(V2/2Zg) where
• f friction factor
• L Length
• D Diameter

29
BERNOULLIS EQUATION

• Z1 (P1/?) (V12/2g) Z2 (P2/?) (V22/2g)
  hP - hL

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
30
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

31
EXAMPLES
32
Reciprocating Pump Characteristic Curve
N2 2 N1
N1
N2
hP (ft)
.
V (gpm)
33
NON-POSITIVE DISPLACEMENT PUMPS
34
(No Transcript)
35
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)

.
.
.
36
PUMPS

• Centrifugal
• Parallel pumps

V2 2V1
2 pumps
HP
HP2 HP1
1 pump
GPM
V
37
PUMPS

• Series (called staging)

2 pumps
HP2 2HP1
HP
V2 V1
1 pump
GPM
V
38
(No Transcript)
39
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 lt PSAT, and the subsequent collapse upon
  migration to a high-press. area.
• causes noise and damage due to erosion and
  fatigue failure.

40
NET POSITIVE SUCTION HEAD

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

pump
41
FANS

42
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

43
(No Transcript)
44
Reading

• Introduction to Naval Engineering
• Chapter 1, pp. 6-8
• Chapter 3, pp. 41-51
• Chapter 10, pp. 175-179
• Principles of Naval Engineering
• Chapter 9, pp. 9-1 - 9-12

45
QUESTIONS ????