Water Hammer in Pipes

Q. A penstock is 2000 m long and the velocity of pressure wave in it is 1000 m/s. Water hammer pressure head for instantaneous closure of valve at the downstream end of pipe is 60 m. If the valve is closed in 4 sec, then the peak water hammer pressure head is equal to

1. 15 m
2. 30 m
3. 60 m
4. 120 m

Q. The velocity of pressure wave in water of infinite extent is 1414 m/s. The velocity of propagation of water hammer pressure in a pipe carrying water and having diameter = 40 cm, pipe thickness = 4 mm, with E (Modulus of elasticity) of the pipe material $=2.1\times {10}^{11}Pa$, and K (Bulk modulus of water) $=2.1\times {10}^{9}Pa,$ is

1. 1410 m/s
2. 2000 m/s
3. 1000 m/s
4. 700 m/s

Q. In a pressure penstock 4500 m long, water is flowing at a velocity of 4 m/s. If the velocity of the pressure wave travelling in the pipe, due to sudden complete closure of a valve at the downstream end, is given as 1500 m/s, what would be the period of oscillation in seconds under frictionless conditions?

1. 6
2. 8
3. 9
4. 11

Q. $\text{If}\rho \text{is density of fluid, then pressure of fluid due to water hammer is directly proportional to-}$

1. $\rho$
2. $\frac{1}{\sqrt{\rho }}$
3. $\sqrt{\rho }$
4. ${\rho }^2$

Q. Which one of the following phenomena in a pipe flow is termed as water hammer?

1. The sudden rise of pressure in a long pipe due to sudden closure of valve.
2. The rise of a pressure in a pipe flow due to gradual closure of valve.
3. The rise of negative pressure.
4. The zero pressure in a pipe flow.

Q. Which of the following statements are true in relation to water hammer phenomenon?

1. It causes surface erosion in pipes.
2. The pressure rise is given by $\rho CU$ for sudden closure of valve.
3. It is accompanied by serious cavitation.
4. The volume modulus of fluid is the relevant fluid property.
5. It is governed by the Reynolds number of the flow.

Select the correct answer using the codes given below:

1. 3 and 5
2. 2 and 4
3. 2 and 5
4. 1, 2, 3 and 4

Q. A liquid of density $\rho$ and bulk modulus K flows with a mean velocity V in a long rigid pipe of diameter D. A sudden closure of a valve at the downstream end of the pipe will produce a maximum water hammer head of

1. $\frac{V\sqrt{\rho }}{g\sqrt{K}}$
2. $\frac{V\sqrt{g}}{\rho \sqrt{K}}$
3. $\frac{V\sqrt{K}}{g\sqrt{\rho }}$
4. $\frac{V\rho }{g\sqrt{K}}$

Q. In a pipeline 1920 m long, the velocity of propagation of pressure wave is 960 m/s. Rapid closure of a downstream valve will entail, when the maximum time for the closure is:

1. 8 s
2. 6 s
3. 4 s
4. 2 s

Q. Let $C_1$ be the velocity of pressure wave travelling along rigid pipe carrying water with its bulk modulus $2.16\times {10}^{9}N/m^2$. Let $C_2$ be the velocity of pressure wave travelling along a rigid pipe carrying oil of relative density 0.600 with its bulk modulus as $1.296\times {10}^{9}N/m^2$ through a similar pipe. What will be the ratio $\frac{C_1}{C_2}$?

1. 0.01
2. 0.1
3. 1.0
4. 10.0

Q. The following parameters relate to flow in a penstock:

1. Water level in the reservoir

2. Density of water

3. Elasticity of water

4. Roughness of pipe

Pressure rise due to water in a penstock depends upon

1. 1 and 2
2. 2 and 3
3. 2 and 4
4. 1, 2, 3 and 4

Q. Consider the following statements:
In order to have cavitation,

1. local velocity is increased so that the local pressure is decreased below vapour pressure

2. elevation is kept so high that the local pressure reduces below vapour pressure

3. general ambient pressure is increased to a very high magnitude

4. water hammer must occur in the system Which of these statements are correct?

1. 2 and 3
2. 3 and 4
3. 1 and 2
4. 1 and 4

Q. Maximum pressure rise due to water hammer in a pipeline$a=\text{area of the pipe};V_0=\text{Velocity,}g=\text{acceleration due to gravity};t=\text{time period;}L=\text{length of the pipeline) is}$

1. $\frac{a{V}_0}{2g}$
2. $\frac{a{V}_0^2}{2g}$
3. $\frac{L{V}_0}{gt}$
4. Independent of the dimensions of the pipe

Q. Match List-I with List-II and select the correct answer using the codes given below the lists:

List-I	List-II
A. Flow development	1. Surge tank
B. Pipe network	2. Entrance length
C. Water hammer	3. Darcy-Weisbach equation
D. Friction loss	4. Hardy-Cross method

1. $A-2,B-4,C-1,D-3$
2. $A-4,B-2,C-3,D-1$
3. $A-2,B-4,C-3,D-1$
4. $A-4,B-2,C-1,D-3$

Q. Which one of the following statements is NOT correct?

1. Water hammer is a phenomenon which occurs due to oscillation of water column away from the valve.
2. Rigid water column theory specifies that water is incompressible and pipe material does not expand.
3. Water hammer occurs under unsteady conditions of flow.
4. Rigid water column theory is used less in practice as it does not reflect field situation.