Transcript ENGINEERING LESSON GUIDE 4 - Technical University of Košice

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
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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

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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
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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
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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

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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
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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

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
Pump Components
DRIVE TYPE
(electric motor,
steam drive, gear
driven, etc…)
IMPELLER
PUMP SHAFT
DISCHARGE
CASING
SUCTION
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 Head
NET STATIC
HEAD
STATIC
DISCHARGE
HEAD
STATIC SUCTION
PRESSURE
PUMP
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
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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

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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
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
Fixed Volume
 Volumetric Flow rate is proportional to
speed
 A relief valve will always be on the
discharge end of the pump

E
X
A
M
P
L
E
S
Reciprocating Pump
Characteristic Curve
hP (ft)
N2 = 2 N1
N1
N2
.
V (gpm)
NON-POSITIVE
DISPLACEMENT PUMPS
Pump Laws
Apply to centrifugal (non-positive displacement)
pumps only
.
VN
H. p  N2
W  N3
V = volumetric flow rate
N = speed of rotation
Hp = pump head
.
W = power required (prime mover)
PUMPS
– Centrifugal:
• Parallel pumps:
V2 = 2V1
2 pumps
HP
1 pump
V
GPM
HP2 = HP1
PUMPS
• Series (called staging):
2 pumps
HP2 = 2HP1
HP
V2 = V1
1 pump
GPM
V
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
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
FANS
Fans
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Operate on the same principle as nonpositive 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 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