Manipulation of Water Hammer Problem by Modification of NRV Valve

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AMAE Int. J. on Manufacturing and Material Science, Vol. 01, No. 01, May 2011
Manipulation of Water Hammer Problem by
Modification of NRV Valve
Authors Names: T. Stalin, C. Manivannan
Department: Department of Mechanical Engineering
College: College of Engineering - Guindy,
Anna University, Chennai 600025, India.
Email: [email protected], [email protected]
Abstract--Water hammer in piping systems produces large
IV. FORMULA TO CALCULATE HAMMERING PRESSURE
dynamic forces which can damage the pipes and supports.
Therefore it is important to minimize the water hammer

By rigid column theory,
effects on the piping system. In this work, a new method for
When valve closed slowly, the elasticity can be neglected.
the red uction of wa ter ha mmer by a ctive measures is
described- that means the reduction of water hammer by
influencing the fluid dynamic conditions of the system. We
are concerned with the effects of the rapid valve closures in

Where, P1= Inlet pressure
pipes connected to wave reflection points. The energy is of
t = closing time in seconds
two kind's Kinetic energy and Elastic energy. Both forms are
v = flow velocity in ft/s
con verted into pressure energy a nd th e ra pidity of the
l = upstream pipe length in feet.
conversion is of the utmost importance in terms of ensuring
da mage th at may resu lt. Su ch energy dissipa tion in a

V. OUTCOMES OF RECENT RESEARCH
controlled non damaging way is discussed in this paper. The
latest outcomes of the research in this area are also discussed

1.
Design a system that minimizes the possibility of water
with their failures in the implementation of these concepts in
hammer.
industries, and the feasibility of our new method
2.
Locate any undersized pipe and replace it with a larger
pipe.
Keywords-Water Hammer; Head;Accumulator; Butterfly valve
3.
Secure loose pipes and to a wall with a pipe damp to
I INTRODUCTION
try to remedy the problem
4.
Wrap some insulation (a towel, an old shirt) around
Water hammer is a pressure surge or leave resulting when
the pipes that are rattling.
a fluid in motion is forced to stop or change direction suddenly.
5.
Install water hammer eliminator if securing the pipes
The pressure wave may cause major problems from noise and
does not solve the problem. It acts like an air chamber or shock
vibration to pipe collapse. By the use of accumulators it is
absorber and it is added in-line to the plumbing system,
possible to reduce effects of hammer pulses.
6.
A slower acting globe or gate valve will prevent the
problem.
II. ENERGY POSSED BY PUMPING OF WATER
7.
Accumulator or de-surge can be used.
The water hammer is a pressure surge or wave caused by
the kinetic energy of a fluid in motion when it is caused to stop
VI. MODIFICATION SUGGESTED
or change direction suddenly. The movement of liquid mass in
In a typical non return valve i.e. butterfly valve, the disc
a pipe is kinetic energy, which is proportional to the mass of
which acts as a control element is modified. Here in the disc
liquid times the square of velocity. For this, most pipe sizing
small holes are to be drilled which acts like the reduction in the
charts recommends keeping the flow velocity at or below 5ft/s
pipe diameter. When there is a reduction in the diameter, the
(1.5 m/s).
energy that is lost by the fluid is high and therefore the adverse
effects of hammering action is decreased or highly nullified
III. EFFECTS OF WATER HAMMER
The modified disc in a butterfly type non return valve
Quick closing valves, positive displacement pumps and
vertical pipe runs can create damaging pressure spikes,
leading to blown diaphragms, seals and gaskets also
destroyed meters and gauges. Liquid for all practical Purpose
is not compressible; any energy that is applied to it is instantly
transmitted. This energy becomes dynamic in nature when a
force such as quick closing valve or a pump applies velocity
to the fluid.
(c) 2011 AMAE
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AMAE Int. J. on Manufacturing and Material Science, Vol. 01, No. 01, May 2011
VII. ADVANTAGES OF BUTTERFLY VALVE
hb- Head lost due to bending
By decreasing the number and the diameter of holes in the
Butterfly valve posses the following advantages.
disc the energy of the fluid can be reduced. Thus from the
1. It can be quickly operated.
above equation it is evident that the energy of the fluid
2. Suited for large flow of fluids or gases with large amount of
decreases. Also the opposed flow of the fluid decreases the
suspended solids.
energy of the flowing fluid. Thus the impact of the water
3. The flow element is a disk of approximately the same diameter
hammer problem is adversely reduced
of the adjoining pipe which rotates on either a vertical or a
horizontal axis.
IX. ANALYSIS AND OUTCOME
VIII. DECREASE OF HEAD
By using the perforation in the disc of a butterfly valve
we are able to decrease the energy of the flowing fluid and
The energy of the flowing fluid can be decreased by
thereby the impact of the water hammer effect is reduced.
using the concept of pressure drop. The more the contact with
Also this method is suitable for chemically active fluids
the pipe materials the more will be the pressure drop. Formula for
because no opening is provided for the surrounding to
the calculation of the main reduction in energy
interfere with the fluid
Head lost due to friction,
The above process can be treated as

... (2.1)
Head lost due to contraction,

We know that by continuity equation,
A1v1=A2v2 ... (2.3)
Where, A1= original flow area A2= reduction in flow area
D - Original diameter of the pipe
d - diameter of the holes in the disc
n - number of holes in the disc
t - thickness of the disc
Now using continuity equation we get, (2.3)
Now the head lost due to contraction,
Therefore the total head lost is given by,
Head lost =
(c) 2011 AMAE
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AMAE Int. J. on Manufacturing and Material Science, Vol. 01, No. 01, May 2011
XII. WEIGHT LOADED ACCUMULATOR
The weight loaded accumulator type consist of a vertical,
heavy-wall steel cylinder, which incorporates a piston with
packings to prevent leakage. A dead weight is attached to
the top of the piston. The force of gravity of the dead weight
provides the potential energy of the accumulator. This type
of accumulator creates a constant fluid pressure throughout
the full volume output of the unit regardless of the rate and
quantity of output. The disadvantage of this equipment is
that it is unsuitable for mobile equipment.
X. CONCEPT BEHIND THE IDEA
According to the law of thermodynamics, Energy
can neither be created nor destroyed. But it can be
transformed from one form of energy to another form of
energy. The energy possessed by pumping of fluid is given
by BERNOUILLI'STHEOREM. It says th at, in an
incompressible flow of fluid, the sum of potential energy,
kinetic energy and pressure energy remains constant at any
XIII. SLIDER CRANK MECHANISM
point of its flow.
Slider crank mechanism, arrangement of mechanical
parts designed to convert straight-line motion to rotary
... (3.1)
motion, as in a reciprocating piston engine, or to convert
rotary motion to straight-line motion, as in a reciprocating
From the above equation, the datum head (z) remains constant
piston pump.
any desired condition of assessment. Hence the two variables
that can vary are pressure and kinetic energy. When we
XIV. SETUP OF NEW MODEL
consider our setup, it resembles the following path of flow
through pipe as the flow in the ORIFICE PLATE.
The movement of the piston with the pressure raise
An orifice plate is a device used for measuring the rate of
or decrease of the weight loaded accmlulator due to the
fluid flow. It uses the same principle as a Venturi nozzle,
increase or decrease of pressure is connected to a slider
namely Bernoulli's principle which states that there is a
crank mechanism. The linear motion is converted into rotary
relationship between the pressure of the fluid and the velocity
motion by this mechanism. This rotary motion is connected
of the fluid. When the velocity increases, the pressure
to the hand lever of the butterfly valve which also triggers
decreases and vice versa. An orifice plate is a thin plate with
the closing or opening according to the pressssure raise or
a hole in the middle. When the fluid reaches the orifice plate,
fall. Thus the overall setup is made.
with the hole in the middle, the fluid is forced to converge to
go through the small hole; the point of maximum convergence
actually occurs shortly downstream of the physical orifice,
at the so-called vena contracta point. Beyond the vena
contracta, the fluid expands and the velocity and pressure
change once again. Here the modified nrv valve acts like a
modified orifice plate, where the pressure head decreases
and serves as a flow control element. Thus the flow control is
achieved by means of a modified nrv valve - orifice plate.
XI. ACCUMULATOR SETUP
Accumulator is a device that stores potential energy
by means of gravity, mechanical springs, or compressed
gasses. The stored potential energy in the accumulator is a
quick secondary source of fluid power capable of doing useful
work as required system. In our setup, a weight loaded
accumulator setup is used.
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AMAE Int. J. on Manufacturing and Material Science, Vol. 01, No. 01, May 2011
XV. CONCLUSION
ACKNOWLEDGEMENT
This method is economically efficient than installing a
We wish to thank the Department of Mechanical
water hammer arrestor. The effect of water hammer is studied
Engineering, CEG, ANNA UNIVERSITY for their financial
and process of reduction of the energy of the fluid is done. The
assistance provided for this paper to present in the conference.
major pressure surge wave is taken by the accumulator and the
slow closing of valve (slider crank mechanism) prevents the
REFERENCES
rapid closing of valves which practically prevents the causing
[1].Bansal, R.K., Fluid mechanics and Hydraulic Machines, Laxmi
of water hammer. This saves the adverse effects of the water
publications (P) Ltd., New Delhi. pp. 850-900.
hammer and protects the valves and pump impellers from damage
[2]. Streeter. V.l., Wylie, E.B., Fluid mechanics, McGraw Hill, 1983.
and making the life of the pipe and pump's impeller to increase.
[3].Micheal J, Pinches and Ashby, J.G.,"POWER HYDRAULICS",
Prentice hall, 1989.
[4]. Dudelyt, A Pease and John J Pippenger,"Basic Fluid Power",
Prentice Hall, 1987.
[5].Anthony Esposito, "Fluid power with Applications", PHI/Pearson
education, 2007, pp. 397- 407,127- 143.
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