4th lab 2013

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Mechanical Engineering Lab

Hydraulics

4th

Year

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Alexandria University

Facul ty o f Engineer ing

Mechanical Engineering Department

Hydraul ics Lab ( 4th

year )

Centrifugal Pump Characteristics

Objectives

It is required to study the performance of a centrifugal pump at different speeds.

Experimental procedure

1. The pump is operated at a certain speed (N).

2. The discharge of the pump is changed using a gate valve installed on the delivery side.

3.

Adjust the speed (N) for each case.

4. For different discharges, the following readings are taken.

Manometric suction head (Hms) by using a pressure gauge, ft.

Manometric delivery head (Hmd) by using a pressure gauge, ft.

U-tube manometer reading (y), cm.

Force (F) by using weights, kgf .

Calculations

1. Pump manometric Head:

Hm = Hmd - Hms

2. Discharge:

1

222

f

u

throat p ipe

throat p iped

yh

gh A A A AC Q

Where,

Cd = 0.94

d pipe = 10 cm

dthroat = 6.86 cm

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y = U-tube manometer reading

u = 13.6

f = 1

3. Efficiency:

η = (O/P) / (I/P)

Where,

O/P = water x Hm x Q

I/P = T x ω

T = F x R

ω = 2π N / 60

Hint: R (brake radius) = 0.3048 m.

Results and Discussion

1)

Draw a schematic diagram for the system.

2) Plot the relation between:

The pump discharge (Q) and the pump manometric head (Hm).

The pump discharge (Q) and the pump efficiency (η).

The pump discharge (Q) and the pump input power (I/P).

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Observations

N1 = rpm

y (cm) Hms (ft) Hmd (ft) F (Kgf ) T = F * R (N.m) I/P (Watt)

h (m) Q (lit/s) Hm (m) = Hmd - Hms O/P (Watt) η

N2 = rpm

y (cm) Hms (ft) Hmd (ft) F (Kgf ) T = F * R (N.m) I/P (Watt)

h (m) Q (lit/s) Hm (m) = Hmd - Hms O/P (Watt) η

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Pelton Wheel Characteristics

Objectives

It is required to study the performance of a Pelton Wheel (turbine) and plot the relation

between the specific speed (Ns) and the mechanical efficiency (η).

Experimental procedure

1. At no flow; read the balance zero reading at the zero position.

2. Start the pump, fully open both the pump discharge valve and the turbine needle valve

then operate the pump at a certain speed.

3. Get the mercury U-tube reading (y) and the turbine inlet head (H).

4. Adjust the turbine brake, load, to get a certain turbine speed (N).

5.

At this speed; use masses and screw to restore original zero position and take the balance

reading.

6. Repeat steps 4 and 5 at different turbine speeds and loads.

Calculations

1. Discharge:

1

222

f

u

throat p ipe

throat p ipe

d

yh

gh A A

A AC Q

Where,

Cd = 0.94

d pipe = 10 cm

dthroat = 6.86 cm

y = U-tube manometer reading

u = 13.6

f = 1

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2.

Brake force:

F = Counter balance masses + zero reading – balance reading

Where, the "Counter balance masses" are the masses added to ensure a net tension force on

the balance.

3. Efficiency:

η = (O/P) / (I/P)

Where,

I/P = water x H x Q

O/P = T x ω

T = F x R

ω = 2π N / 60

Hint: R (brake radius) = 0.46 m.

4. Specific speed:

Where; O/P in kw.


Plot the relation between the specific speed (Ns) and efficiency (η) for the Pelton Wheel

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Observations

Balance zero reading = (kgf )

Counter balance masses (kg ) y (cm) H (ft) N (rpm) Balance reading (kgf )

Q (m3/s) I/P (watt) F (N) ω (rad/s) T (N.m) O/P (watt) Ns(SI units) η (%)

7.3

6.9

5

3.7

1040

1000

960

900

6

6

6

6

4

74

74

74

74

f

3.5

3.5

3.5

3.5

F (N

1.9

5.8

24

37

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Forced Vortex

Objectives

It is required to study the pressure distribution on the bottom of a tank filled with liquid and

subjected to forced vortex at different rotational speeds.

Experimental Procedure

1. Turn on the motor switch.

2. Adjust the speed regulator at certain rotational speed.

3.

Wait for steady flow (piezometers readings remain constant).

4. List down the readings of the 12 piezometer tubes.

5. Change the rotational speed.

6.

List down the readings of the 12 piezometer tubes at the new speed.

Observations

Tube No.Piezometer tube reading (cm)

N1 (rpm) = … N2 (rpm) = …

1

2

3

4

5

6

78

9

10

11

12


Draw the distribution of the pressure head on the tank bottom at the two speeds N 1 and N2

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Secondary Losses in Bends and Fittings

Objectives

It is required to demonstrate the secondary losses through different types of bends and fittings.


1.

Close the regulation valve and start the centrifugal pump.

2. Open the valve partially.

3. Wait for steady flow (Piezometers readings = constant).

4.

Read the differential readings of the Piezometers connected to the mitre, the elbow, the

short bend, the enlargement and the contraction.

5. Read the initial volume in the collection tank V1.

6.

Observe the time (t) to increase the collected volume to V2.

7. Increase the valve opening.

8. Repeat the experiment two times.

9. After recording all the required readings, close the valve gradually then stop the

centrifugal pump.

Notes:Pipe area : 301.7 mm2

Enlargement pipe diameter : 26.2 mm

Contraction pipe diameter: 19.48 mm

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Observations

Experiment No. 1 Experiment No. 2

Type of fittingh

(mm)

V1(lit.)

V2(lit.)

t

(Sec.)h

(mm)

V1(lit.)

V2(lit.)

t

(Sec.)

Mitre

Elbow

Short bend

Enlargement

Contraction

Calculations

)tEnlargemen(22

)-(

K=h

)nContractio(22

K=h

) bendShort&ElbowMitre,(2

K=h

t

VVQ

2

1

2

2

2

21

2

1

2

2

2

2

2

12act

g g

g g

g

Where,

v1 = upstream velocity

v2 = downstream velocity

Results and Discussions

List down the value of the coefficient of loss (K) for each type of fitting.

Comment on the results.

K (Exp. No. 1) K (Exp. No. 2) K av

Mitre

Elbow

Short bend

Enlargement

Contraction

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Performance of a Pressure Relief Valve

Objectives

It is required to study the performance of a direct-acting pressure relief valve.


1)

Close the throttle valve completely then, unload the pressure relief valve.

2)

Set the pressure relief valve approximately to 50 bar then, open the throttle valve

completely.

3) Close the throttle valve in several steps, measure and note down the system pressure and

the flow rate through the pressure relief valve.

Observations

Throttle valve Open Closed

Psystem (bar)

Qrelief (l/min) Zero


1) Describe the operation of the circuit.

2) Plot the pressure-flow relationship for the pressure relief valve.

3)

List down all components used in the circuit.

4) Draw the hydraulic circuit diagram.

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Regenerative Circuit Characteristics

Objectives

It is required to study the behavior of a regenerative circuit and to compare it with that of a

normal circuit.


1)

Using the 4/2 DCV as a 3/2 DCV (by plugging one of its ports), extend the double-acting

cylinder and notice the extension speed and the pressures upstream and downstream the

cylinder.

2)

Using the 4/2 DCV normally, extend the double-acting cylinder and notice the extension

speed and the pressures upstream and downstream the cylinder.

Observations

Pupstream (bar) Pdownstream (bar) Extension Time

Regenerative circuit

Normal circuit



2) Compare the extension parameters (extension time, force) for the regenerative and the

normal circuits.

3) List down all components used in the circuit.

4) Draw the hydraulic circuit diagram for both the regenerative and the normal circuits.

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Facul ty of Engineer ing



year )

Control of a Double Acting Cylinder in a Pneumatic System

Objectives

It is required to study how to connect a pneumatic circuit to perform extension and retraction

of a double-acting cylinder.


Use the 3/2 Push- button DCV’s to actuate the 5/2 pilot operated DCV which controls the

extension and retraction of the double-acting cylinder.

Observations

Notice how the air is transmitted through the pneumatic lines from the air source to the

cylinder through the directional control valves to perform the extension and the retraction of

the double acting cylinder.




3) Draw the pneumatic circuit diagram.

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Alexandria UniversityFaculty of Engin eering



year )

Speed Control for a Position-Dependant Double Acting

Cylinder

Objectives

It is required to study how to connect a pneumatic circuit to perform controlled speed

piston extension and retraction functional sequence for a double-acting cylinder.


Use the 3/2 Push-button DCV to actuate the 5/2 pilot operated DCV which controls the

extension and retraction of the double acting cylinder through two mechanical actuated

3/2 DCV’s. Notice the extension and retraction strokes and how they are controlled.

Observations

Notice how the air is transmitted through the pneumatic lines from the air source to the

cylinder through the directional control valves to perform successive extension and

retraction of the double acting cylinder.




3)

Draw the pneumatic circuit diagram.

4th lab 2013

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