Hydraulics Lab - ECIV 3122
Experiment (8): Minor Losses
Experiment No. (8)
Minor Losses
Purpose:
To determine the loss factors for flow through a range of pipe fittings including
bends, a contraction, an enlargement and a gate-valve.
Theory:
The energy balance between two points in a pipe can be described by Bernoulli
equation, given by
V12 p 2
V22
 z1 

 z2 
 hL

2g 
2g
p1
Head loss hL includes the sum of pipe friction losses hf and all minor losses. Pipe
friction losses are assumed to be negligible in this experiment.
If
p1

 z1  h1,
p2

 z 2  h2, then
V 2 V 2 
hm  h1  h2   1  2 
 2g 2g 
h1 & h2 are peizometer readings, hm is the minor losses.
The energy loss which occurs in a pipe fitting (so-called secondary loss) is commonly
V2
V 2 
expressed in the form:
hm  K

K  hm /
2g
 2g 
Apparatus:
1. Energy Losses in Bends and Fittings Apparatus consists of:
1. Sudden Enlargement
2. Sudden Contraction
3. Long Bend
4. Short Bend
5. Elbow Bend
6. Mitre Bend
7. Gate Valve.
Figure 1:minor losses apparatus
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Hydraulics Lab - ECIV 3122
Experiment (8): Minor Losses
2. The following dimensions from the equipment are used in the appropriate
calculations.

Internal diameter of pipe: d = 0.0183 m

Internal diameter of pipe at enlargement outlet and contraction inlet :
d = 0.0240 m
3. For the gate valve experiment, pressure difference before and after gate is
measured directly using a pressure gauge. This can then be converted to an
equivalent head loss using the equation:
1 bar = 10.2 m water
Procedure:
It is not possible to make measurements on all fittings simultaneously and, therefore,
it is necessary to run two separate tests.
PART (A)
1. Set up the losses apparatus on the hydraulic bench so that its base is horizontal by
adjusting the feet on the base plate if necessary. (this is necessary for accurate
height measurements from the manometers). Connect the test rig inlet to the bench
flow supply and run the outlet extension tube to the volumetric tank and secure it
in place.
2. Fully open the gate valve and the outlet flow control valve at the right hand end of
the apparatus.
3. Close the bench flow control valve then start the service pump.
4. Gradually open the bench flow control valve and allow the pipework to fill with
water until all air has been expelled from the pipework.
5. In order to bleed air from pressure tapping points and the manometers close both
the bench valve and the test rig flow control valve and open the air bleed screw
and remove the cap from the adjacent air valve. Connect a length of small bore
tubing from the air valve to the volumetric tank. Now, open the bench valve and
allow flow through the manometers to purge all air from them; then, tighten the
air bleed screw and partly open both the bench valve and the test rig flow control
valve.
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Hydraulics Lab - ECIV 3122
Experiment (8): Minor Losses
Next, open the air bleed screw slightly to allow air to enter the top of the
manometers, re-tighten the screw when the manometer levels reach a convenient
height.
6. Check that all manometer levels are on scale at the maximum volume flow rate
required (approximately 17 liters/ minute). These levels can be adjusted further by
using the air bleed screw and the hand pump supplies. The air bleed screw
controls the air flow through the air valve, so when using the hand pump, the
bleed screw must be open. To retain the hand pump pressure in the system, the
screw must be closed after pumping.
7. If the levels in the manometer are too high then the hand pump can be used to
pressurise the top manifold. All levels will decrease simultaneously but retain the
appropriate differentials.
If the levels are too low then the hand pump should be disconnected and the air
bleed screw opened briefly to reduce the pressure in the top manifold.
Alternatively the outlet flow control valve can be closed to raise the static pressure
in the system which will raise all levels simultaneously.
If the level in any manometer tube is allowed to drop too low then air will enter
the bottom manifold. If the level in any manometer tube is too high then water
will enter the top manifold and flow into adjacent tubes.
8. Adjust the flow from the bench control valve and, at a given flow rate, take height
readings from all of the manometers after the levels have steadied. In order to
determine the volume flow rate, you should carry out a timed volume collection
using the volumetric tank. This is achieved by closing the ball valve and
measuring (with a stopwatch) time taken to accumulate a known volume of fluid
in the tank, which is read from the sight glass. You should collect fluid for at least
one minute to minimize timing errors. ( note: valve should be kept fully open.)
9. Repeat this procedure to give a total of at least five sets of measurements over a
flow range from approximately 8 - 17 liters per minute.
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Hydraulics Lab - ECIV 3122
Experiment (8): Minor Losses
PART (B)
10. Clamp off the connecting tubes to the mitre bend pressure tappings (to prevent air
being drawn into the system).
11. Start with the gate valve closed and open fully both the bench valve and the lest
rig flow control valve.
12. open the gate valve by approximately 50% of one turn (after taking up any
backlash).
13. For each of at least 5 flow rates, measure pressure drop across the valve from the
pressure gauge; adjust the flow rate by use of the test rig flow control valve. Once
measurements have started, do not adjust the gale valve. Determine the volume
flow rate by timed collection.
14. Repeat this procedure for the gate valve opened by approximately 70% of one turn
and then approximately 80% of one turn.
Data and results:
Table 1. Raw Data for All Fittings Except Gate Valve
Case No.
Volume
Time
Piezometer Readings
(mm)
Enlargement
Contraction
Long Bend
Short Bend
Elbow
Mitre Bend
(L)
(sec)
1
2
3
4
5
6
7
8
9
10
11
12
I
13
95.93
243
248
247
237
246
244.5
237
228
220
206
190
171
II
13
75.8
255
263
262
245
259
256
245
231
220
198
175
145
4
III
21
107.06
265
275
274
253
272
267
253
234
219
191
162
122
IV
24
108.53
276
289
287
260
284
279
260
237
219
183
147
98
V
25
93.14
299
319
317
276
309
301
277
243
217
165
115
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Hydraulics Lab - ECIV 3122
Experiment (8): Minor Losses
80% Opened
70% Opened
50% Opened
Table 2. Raw Data for Gate Valve
Case No.
Volume (L)
Time (sec)
Gauge
Reading
(bar)
I
40
84.12
II
25
61.21
III
24
67.02
IV
19
63.49
V
14
65.22
Red
(upstream)
1.1
0.79
0.6
0.4
0.2
Black
(downstream)
0.09
0.05
0.01
0
0
40
57.53
40
68.04
35
65.39
30
64.9
25
71.4
Red
(upstream)
0.4
0.3
0.23
0.16
0.09
Black
(downstream)
0.02
0.01
0
0
0
40
55.45
40
61.39
40
67.31
40
83.97
40
96.78
Red
(upstream)
0.2
0.17
0.11
0.08
0.03
Black
(downstream)
0.07
0.05
0.02
0
0
Volume (L)
Time (sec)
Gauge
Reading
(bar)
Volume (L)
Time (sec)
Gauge
Reading
(bar)
Calculations:
Table 3. Minor Head Losses of All Fittings Except Gate Valve
Case No.
I
II
Q (m3/sec)
V (m/s)
V2/2g (m)
Minor Head Losses (m)
Enlargement Δh
Δh +V12/2g- V22/2g
Contraction Δh
Δh +V12/2g- V22/2g
Long Bend
Short Bend
Elbow
Mitre Bend
5
III
IV
V
Hydraulics Lab - ECIV 3122
Experiment (8): Minor Losses
Table 4. Loss Coefficients for All Fittings Except Gate Valve
Case No.
I
II
III
IV
V
Loss Coefficients
Q (m3/sec)
V (m/s)
V2/2g (m)
Enlargement
Contraction
Long Bend
Short Bend
Elbow
Mitre Bend
80% Opened
70% Opened
50% Opened
Table 5. Equivalent Minor Head Loss and Loss Coefficient for
Gate Valve
Case No.
Q (m3/sec)
V (m/sec)
I
II
V2/2g (m)
Minor
Head Loss
(m)
Loss
Coefficient
Q (m3/sec)
V (m/sec)
V2/2g (m)
Minor
Head Loss
(m)
Loss
Coefficient
Q (m3/sec)
V (m/sec)
V2/2g (m)
Minor
Head Loss
(m)
Loss
Coefficient
6
III
IV
V
Hydraulics Lab - ECIV 3122
Experiment (8): Minor Losses
Questions ..
1. For Part A, prepare plots that show the effect of dynamic head on minor head loss
V2
(i.e. plot graphs of head loss (∆h) against dynamic head ( 2g)), and the effect of flow rate on
loss coefficients (i.e. K against volume flow rate Q).
2. For Part B, prepare plots that show the effect of dynamic head on equivalent head
V2
loss (i.e. (∆h) against ( 2g)), and the effect of flow rate on loss coefficients (i.e. K
against volume flow rate Q).
3. Comment on and explain previous relationships.
a. Is it justifiable to treat the loss coefficient as constant for a given
fitting? Explain.
b. How does the loss coefficient for the gate valve vary with the extent of
the opening of the valve? Explain.
4. Does the static pressure increase or decrease for the enlargement and contraction?
Explain the increase or decrease in static pressure.
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