HYDRAULICS Class 4.ppt

FIRE ENGINEERING
SCIENCE
HYDRAULICS

CHARACTERISTICS OF FLOW IN HOSE
AND PIPELINES (Velocity, or rate of flow)
The laws governing the velocity of
particles of water correspond to the same
laws that govern free falling bodies.
Ignoring air resistance, free falling bodies
accelerate at the rate of 9.81 metre per
second per second or 9.81 meters per
second squared (9.81m/s²).

Thus, the velocity of any falling body at
the end of a given number of seconds,
after falling from rest, is found by
multiplying the number of seconds (time)
by the constant g.
v = gt,
where v = velocity in metres per second
(m/s),
g = gravity, and
t = time in seconds.

What is the velocity of a free-falling
droplet of water at the end of 10 seconds
from rest?

What is the velocity of a free-falling
droplet of water at the end of 10 seconds
from rest?
v = gt
= 9.81 x 10
= 98.1 seconds

The velocity of a free-falling droplet of
water is 19.62 m/s when it strikes the
ground calculate how long the droplet of
water fell for.

The velocity of a free-falling droplet of
water is 19.62 m/s when it strikes the
ground calculate how long the droplet of
water fell for.
v = gt v = gt
t = v/g 19.62 = 9.81 x t
= 19.62 /9.81 19.62 / 9.81 = t
= 2 seconds 2 = t
t = 2
seconds

If the distance fallen = average velocity x
time
Then the distance (H) = v x t = gt x t
2 2
= gt2 or
2
= ½ gt2
Where H is in metres (m)

If the distance or height through which a
body
falls is compared with the velocity it attains,
it is
found that there is a direct relationship.
V = gt H = gt2
2
H = ½ gt2

If the distance or height through which a
body
falls is compared with the velocity it attains,
it is
found that there is a direct relationship.
From this relationship the following
formulas
are derived:
v = √2gH or 4.43 √H ≈ 4.4 √H

These laws apply equally to the flow of
water through a pipe, where the particles
have a certain velocity due to height
(head) from which they have fallen (if
gravity fed) or due to the pressure applied
by some other source, such as a pump.

The value of this formula can be seen when
calculating the velocity of water issuing
from a
nozzle.
What is the velocity of the water issuing
from a
nozzle when the nozzle pressure is 5 bar?

Thus far, the only formula we have to
calculate
velocity is:
v = gt, v = √2gH or 4.43 √H or 4.4 √H
We are given a nozzle pressure of 5 bar
and we
have a formula with a pressure head (H) or
height.  we can calculate H
H = P × 10.19 (metre)

v = gt, v = √2gH or 4.4 √H
H = P × 10 = 5 x 10 = 50
we can now calculate v
v = 4.4 √H
= 4.4 √50
= 4.4 x 7
= 31 m/s

AND PIPELINES (Velocity of water in hose
and pipes)
To enable water to flow along a hose or a
pipe,
a difference in head or pressure at the two
ends is necessary.

and pipes)

and pipes)
The amount of water a hose or pipe will
transmit or convey in a given time depends
on :
(i) Its size (cross-sectional area)
(ii) The speed at which the water is
passing through it (i.e velocity)

and pipes)
The formula for calculating the quality of
water
passing through a hose or pipe is:
Q = v x A
Where Q is the quantity of water in cubic
metres per second, v is velocity in metre
per second and A is the cross-sectional
area of the pipe in square metres.

and pipes)
Firemen prefer however, to deal in
discharges
from pipes or hose in litres per minute and
to
refer to the diameter of such hose or pipes
in
millimetres.
Taking the formula Q = v x A and
transposing,

and pipes)
v = 21.2L or v ≈ 20L
d2 d2
Where L the flow in litres per minute and
d is diameter in millimetres

and pipes)
Conversely, if the velocity is known the
discharge can be found by transposing the
formula to:
L = vd2
20

and pipes)
What is the velocity of water in a 70 mm
diameter hose if the discharge is 1000 litres
per
minute?
Use the formula: v = 20L
d2

and pipes)
What is the velocity of water in a 70 mm
diameter hose if the discharge is 1000 litres
per
minute?
v = 20L = 20 x 1000
d2 702
= 20,000
4,900
= 4.08 m/s or 4 m/s

and pipes)
It is apparent that there is a direct
relationship
between velocity and quantity delivered;
doubling the velocity will result in twice the
quantity being delivered.

and pipes)
The velocity at which the water travels
through
a pipe or hose is also dependent on the
pressure applied or the difference in head,
but
it will be shown that there is another factor
–
loss of head due to friction which also plays
a

AND PIPELINES (Loss of pressure due to
friction)
To propel water through a hose or pipe,
work
has to be performed to overcome friction,
which is caused by the particles of which
water
is composed rubbing against each other
and
against the walls of the hose or pipe
through
which the water is passing.

friction)
There are five (5) principal laws governing
loss
of pressure due to friction, namely
 Friction loss varies directly with the length
of pipe.
 For the same velocity, friction loss
decreases directly with the increase in
diameter.
 Friction loss increases directly as the
square of the velocity.

friction)
 Friction loss increases with the
roughness of the interior of the pipe.
 Friction loss, for all practical purposes is
independent of pressure.

Friction loss varies directly with the length of
pipe
This is obvious, as the longer the hose the
more pressure is required to pump the
water
through. If the length of hose is doubled,
the
loss of pressure due to friction is doubled.

For the same velocity, friction loss
decreases directly with the increase in
diameter
This is extremely important, for if the diameter of
a
pipe is doubled, the surface area is doubled, but
the
cross-sectional area is quadrupled (the cross-
sectional area being proportional to the square
of
the diameter). Therefore for any given velocity, if
the
diameter of the hose is doubled, the quantity of
water is increased to four times, and the loss of
pressure due to friction is consequently halved.

Friction loss increases directly as the
square of the velocity
This is another very important factor, as, if the
velocity of the water is halved, the loss of
pressure
due to friction is reduced to (½)2 or one-quarter.
This has its most important application when
pumping over long distances. If 2000 litres of
water
per minute are being delivered through one line
of
hose with a loss of pressure due to friction of 6
bar, the act of twinning the hose and 1000
litres/min

Friction loss increases with the roughness
of the interior of the pipe
That friction increases with roughness is
apparent when attempting to rub one’s
finger
over sandpaper compared with a polished
surface. Similarly, it is more difficult to
force
water through a pipe with a rough interior,
than with a smooth inside surface.
The degree of internal roughness of a

Friction loss, for all practical purposes is
independent of pressure
Experiments show that loss of pressure due to
friction is independent of pressure or head at
which
the system is operating. Thus, if the friction loss
for a
given flow rate in a certain line of hose or pipe is
such that a pump pressure of 7 bar is required
to
maintain a nozzle pressure of 3 bar, then it will
be
found that in order to maintain a nozzle pressure
of

Friction loss, for all practical purposes is
independent of pressure
With hose, increase in pressure may result in
certain
indirect effects, such as a slight stretching giving
an
increase in cross-sectional area and thus a
slight
reduction in friction loss. On the other hand, a
rise in
pressure may result in some increase in length
and,
therefore, a somewhat greater frictional loss.
These

AND PIPELINES (Calculation of friction
loss)
To force water through a hose, sufficient
pressure or head must be available at the
pump to overcome all the factors affecting
friction loss, and to provide a margin which
will enable an efficient jet to be maintained
with a plain nozzle at the branch, or, in the
case of a spray with a diffuser branch, to
break
up the water stream and project the spray
effectively.

loss)
The formula for the head loss due to friction
in
a length of pipe or is given as:
Hf = 2flv2
Dg where,
Hf = head loss due to friction (metres)
f = frictional factor
l = length of pipe or hose (metres)
v = velocity of water (m/s)
D = diameter of pipe or hose (metres)

loss)
It is important to remember when using this
formula that all measurements must be in
metres and the result will give the friction
loss
in metres head.
But it is useful to know the loss of pressure
in
bar rather than in metres head and to
express

loss)
The formula can be converted to:
Pf = 20flv2
d where,
Pf = pressure loss due to friction (bar)
f = frictional factor
l = length of pipe or hose (metres)
v = velocity of water (m/s)
d = diameter of pipe or hose (millimetres)

loss)
A line of 90 mm hose is 500 metres long.
Water is flowing through it at a velocity of
2
metres per second. Using a friction factor
of
0.007, what is the loss of pressure due to
friction?
Pf = 20flv2
d

loss)
A line of 90 mm hose is 500 metres long. Water is flowing
through it at a velocity of 2 metres per second. Using a
friction
factor of 0.007, what is the loss of pressure due to
friction?
Pf = 20flv2
d
f = 0.007, l = 500 metres, v = 2 m/s,
d = 90 mm
Pf = 20 x 0.007 x 500 x 22
90

loss)
Pf = 20flv2
d
In this formula, one requires to know the
velocity in metres per second. Firemen,
however, generally deal instead with
discharges
in litres per minutes (L). We can therefore
substitute 21.2L for v
d2
giving the formula:

loss)
Pf = 9000flL2
d5

loss)
Water is being discharge at 764 litres per
minute. Using a friction factor of 0.007,
what is
the loss of pressure due to friction?
Pf = 9000flL2
d5

loss)
Water is being discharge at 764 litres per
minute. Using a friction factor of 0.007,
what is
the loss of pressure due to friction?
Pf = 9000flL2
d5
= 9000 x 0.007 x 500 x 7642
90 x 90 x 90 x 90 x 90
= 3.12 bar

loss)
It should be borne in mind that it is
impossible
to calculate friction losses with any great
degree of accuracy when dealing with fire
service hose, as there are a number of
factors
which affect the result. For example, hose
will
increase both in diameter and in length
when

loss)
Test have been carried out with hose of
various
sizes, and for all practical purposes the
friction
factor (f) of the fire service hose is shown:
Type of hose Friction factor
Non-percolating hose
90 mm diameter fitted with
standard instantaneous

loss)
Type of hose Friction factor
All other hose 0.005
Percolating hose
Excluding 90 mm hose 0.010

loss)
Calculate the pressure required at the
pump to
maintain a branch pressure of 4 bar at a 25
mm
nozzle at the end of 150 metres of 70 mm
non-
percolating hose at a discharge of 830 litres
per
minute.
Pf = 9000flL2

loss)
Calculate the pressure required at the pump to maintain a
branch pressure of 4 bar at a 25 mm nozzle at the end of
150
metres of 70 mm non-percolating hose at a discharge of
830
litres per minute.
Pf = 9000flL2
d5
= 9000 x .005 x 150 x 8302
70 x 70 x 70 x 70 x 70
= 2.77 bar

HYDRAULICS Class 4.ppt

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to HYDRAULICS Class 4.ppt

Similar to HYDRAULICS Class 4.ppt (20)

Recently uploaded

Recently uploaded (20)

HYDRAULICS Class 4.ppt