Water hammer is a pressure surge or wave that occurs when water flowing through a pipe is forced to stop or change velocity suddenly, such as when a valve closes rapidly. This can cause very high pressure spikes that can damage pipes and equipment. The Joukowsky equation describes the relationship between pressure change and change in flow velocity. Protective devices like water hammer arrestors, surge tanks, and soft starters can help reduce the effects of water hammer by slowing changes in flow.

1. WATER HAMMER
NAVEEN SUDHARSAN
MT14WRE010

2. What is Water Hammer?
 Water hammer is a pressure surge or wave resulting when a fluid in motion
is forced to stop or change the velocity
 A water hammer commonly occurs when a valve closes suddenly at an
end of a pipeline system, and a pressure wave propagates in the pipe. It is
also called hydraulic shock.

3. Reasons
Immature
operation
of valve
Sudden
stoppage
of pump
Power
outage

4. Sudden Closure Of A Valve

5. Fluid Mechanics with
Engineering
applications by
Joseph B Franzini &
E.John Finnemore
Mechanism

6. Mechanism
Sudden Closure of
the valve
•Fluid lamina near to the
valve compressed
•This compression
reaches upstream end
of the pipe(t=L/a)
At the Reservoir
•Unbalanced condition
at the reservoir pressure
•Flow from pipe to
reservoir starts as the
wave moves
downstream
•Reservoir pressure
unchanged(2L/a)
Low pressure
moves upstream as
waves
•Makes the velocity of
flow zero again
•But the fluid in the pipe
will be expanded(3L/a)
At the Reservoir
•Unbalanced condition
•Due to Negative
pressure in the pipe
•Flow towards pipe
starts(4L/a)
Fluid Mechanics by
Victor L Streeter, E
Benjamin Wylie & Keith W
Bedford

7. Water Hammer Equations
Joukowsky (1898) eqn
∆𝑃 = 𝜌𝐶 𝑝∆𝑉
 Where ∆𝑃 is change in pressure
 𝜌 density
 𝐶 𝑝 is the velocity of wave (1496 m/s at 25°C in water)
 ∆𝑉 is change in velocity
 This equation can be used only for rapid closure( t < 2L/𝐶 𝑝)

8. Water hammer equations for all conditions:
 Equation of motion

𝜕𝑉
𝜕𝑡
+ 𝑔
𝜕𝐻
𝜕𝑥
+
𝑓𝑉 𝑉
2𝐷
= 0
 Equation of continuity

𝜕𝐻
𝜕𝑡
+
𝑎2
𝑔
𝜕𝑉
𝜕𝑥
= 0
These two pde are solved using method of
characteristics.

9.  Consider a 500mm dia pipeline, L = 8000 m, 𝐶 𝑝 =1000m/s
& v = 2 m/s, a gate valve is closed in 5 seconds.
Calculate the pressure surge. Calculate the force
exerted on the gate.
 𝑇𝑟 =
2𝐿
𝐶 𝑝
= 16 𝑠 > 5 𝑠
 Joukowsky’s equation may be applied.
 ∆𝑃 = 𝜌𝐶 𝑝∆𝑉
 ∆𝑃 = 20 𝑋 105 𝑁
𝑚2
 Area = .196 𝑚2 ≈ 0.2 𝑚2
 𝐹𝑜𝑟𝑐𝑒 𝐹 = 𝑃. 𝐴 = 20 𝑋 105 𝑋 0.2 = 400000 𝑁
 F = 400 𝐾𝑁

10. Applications
Hydraulic Ram
works with the
principal of Water
hammer
Leaks can
sometimes be
detected using
water hammer
The US Navy is
conducting
field trials for
mine clearing
using water
hammer.

11. Effects of Water Hammer
Damage to pipes, fittings, and valves, or any connected
equipment causing leaks and shortening the life of the system
Bursting of pipes can occur if the pressure is high enough
Water hammer can have devastating effects on pump system

13. Devices for Protection from Water
Hammer
 Soft Starters
 Slow closing valves

14.  Variable Frequency Devices
 Water Hammer Arrestors

15.  Surge Tanks
 Pressure Release Valves

16. Conclusions
Water hammer can cause severe problems in the system if
not designed properly. So at the time of designing of the
system potential water hammer problems should be
considered for thorough analysis. And proper methods or
devices are to be used so as to assure the proper
functioning of the system and to lessen the effect of water
hammer
Water hammer is useful in certain cases as hydraulic ram,
mine clearing etc.

17. References
 Fluid Mechanics with Engineering Applications by Joseph B Franzini & E
John Finnemore, The McGraw Hill Companies, 1997
 Fluid Mechanics by Victor L Streeter, E Benjamin Wylie and Keith W Bedford,
The McGraw Hill Companies, 2010 reprint
 KSB Know how, Vol 1 Water hammer, KSB Aktiengesellschaft, Johann-Klein-
Straße 9,67227 Frankenthal
 en.wikipedia.org/wiki/Water_hammer