In this article, we will learn what is water hammer? Along with we will capture the basics, definition, causes, effects, how to fix or stop, etc.
Let’s try to understand the basics of water hammer. We all know liquids are barely compressible, this means their volume can’t be changed under the application of pressure.
So when we stop it suddenly pressure waves to get created and it has nowhere to go. This creates big noise, we call it a water hammer. Plumbing is the most under-acknowledged modern marvel that is for sure, we will realize this by this example.
If the pipeline is of 1m diameter and its length is 100 km then the mass of water inside is about 80 million kg. If the operator closes the valve fast, it will create a huge spike in pressure which will cause rupture to pipes, which will be as devastating as bombs.
Water travels through pipelines with a velocity that is dependent on,
This water moving inside pipes when stopped suddenly by the operator by closing valve or by another cause, there is a sudden rise in pressure of water because the momentum of water got destroyed.
Hence, water hammer is defined as a phenomenon of sudden pressure rise in pipes. It is also called as hammer blow as well.
This pressure rise is dependent on many variables such as
This phenomenon is very important because the rise in pressure is so steep that it may lead to the bursting of pipes and may lead to a big accident.
When water is stored at tanks or in dams, it contains some form of energy by virtue of its position which we called as potential energy.
This potential energy is the product of density, gravitational acceleration, and height at which water is stored.
When this water is coming through such high head to lower side, this potential energy is getting converted into kinetic energy.
K.E = 1/2 mv2
It is dependent on mass (m) and square of velocity (v).
So when water running at such a high speed is stopped abruptly then this energy will get converted into pressure energy which will be dependent on the speed at which the velocity of fluid was reduced.
If it will be sudden then due to sudden change pressure rise will be sudden, if it is gradual pressure rise will be gradual. This all phenomenon happens due to the conversion of one form of energy into another.
Wave will travel from valve to tank and from tank to valve, T
To understand this we need to go through this example
Consider a long pipe is carrying liquid and valve is attached to it at extreme end. On one end there is a tank and on another end, the valve is attached. This valve is being closed slowly.
So the mass of liquid in the pipe is m = ρ A L
Let us just assume that closure of valve is being done such that liquid flowing through the pipe is brought to halt with uniform de-acceleration. From initial velocity V to zero in time t.
Condition – when the valve is closed gradually
Retardation of water = (v – 0)/t = v/t
The axial force which is producing retardation, F1
The force created by pressure wave, F2
When we equate these forces,
Then the head of pressure H,
So the head of pressure will be, H = L v/gt
The closure of the valve is done very gradually when t > 2L/C
Closure of valve is said to be instantaneous when t < 2L/C
Where C = Velocity of the pressure wave.
After getting the basic idea about water hammer, let’s check what causes water hammer. So, what are the main causes of water hammer?
The causes of water hammer shall be as follows,
Cause#1 Sudden Valve Closure
Sudden closure of valves, it may create water hammer sound or noise continuously. Think it in a simple example. If you run in a track, suddenly someone stops you! You will feel a shock.
Now, if you run you faster, your shock will be more and if you run with lower speed, your shock will be less.
Cause#2 Volume Difference Between Steam & Water & Heat Loss
In case of condensate pipes, due to heat loss, condensate starts to change its phase into water. As steam occupy 1600 times more volume than water, if steam changes its phase into water, a huge vacuum will be created. Water will try to filled that vacuum and can create water hammer.
Cause#3 Velocity Difference Between Steam & Water
In case of condensate pipes, as the velocity of steam is 10 times of water velocity, steam go faster in the pipe. Now, steam starts to condense and the amount of condensate increases in the pipe. Many times, this condensate fill the pipe and create a barrier, which causes a huge pressure difference between the two sides of that barrier.
Downstream pressure will be drastically reducing and the water will try to fill that gap & create water hammer.
Cause#4 Float Valve Stability
If float valves are not stable, and it up and down as well as creating an web into the system,
Cause#5 Blocking of Suction Pipe
Blocking of suction pipe can also be a reason for water hammer.
Cause#6 Fitting Problems
Improper fittings of pipes or between pump and piping may create water hammer.
Cause#7 Trip of Pump
In many cases, trip of pump may be a reason of creating shock in pipes and creates water hammer.
Apart from above, there may some other reasons like,
We have learned what is the cause of water hammer in pipelines? Let’s see the effects of water hammer one by one,
Water can make a total system failure by a sudden surge in the piping system. It does damage to equipment such as flow meters, pressure gauges, etc. because such instruments have a delicate inner structure that is not designed to withstand such high-pressure waves.
As we have learned that shock due to water hammer depends on many factors. A big shock can fail the entire system, however, a continuous small shock can damage the pump, its associated equipment, etc.
Due to this uneven pressure or shock, the associated piping system will be damaged, which can damage the entire system as well.
It will incur leakage in the piping system.
Due to leakage in the piping or pipelines, which will reduce the head requirements, as well as the efficiency of the system.
Due to the water leakage, running electrical system may come into contact with water and the electrical system will be damaged.
Short circuits may happen and electrical hazards may be encountered, which is totally unsafe for the workers.
Due to high shock, supports of piping or pipelines may be damaged.
Due to continuous problems, it increases the maintenance issues.
Due to the shock, water hammer creates sound or noise.
Damage and destruction of piping leading to the industrial accident. Especially steam plants, where condensate travels at slow speed but steam always travels at high speed, in such cases water gets dragged by steam at very high speed which is 10 times speed of the water.
In such cases, water pressure becomes very high and may incur a big accident.
Let’s see how to stop or fix water hammers?
It is very difficult to eliminate water hammer from the steam systems, however, we can minimize it with the below steps:
How to Avoid Water Hammers using Air Vessels?
It is pretty much simple in design. It is made of a big container and it is joined to the pipe. It is filled with air and water. As air is less dense than water it gets trapped by water coming from pipes.
When a shock wave appears in the pipeline it enters this vessel and air gets compressed for a time being due to this pressure. So this extra energy got absorbed.
Limitations of Air Vessels
With time this air gets absorbed in water and water starts to occupy space of air. So whole effectiveness of absorbing shock decreases.
Also, there are chances of the formation of bacteria in such areas.
They are the same as air vessels. Just they are cleverly designed in such a way that water and air don’t make contact. Air is sealed in this chamber by providing a plunger with tightly sealed O rings.
This plunger is free to rotate up and down. So when a water shock wave comes this plunger moves up and compresses this air inside it. This way shock gets absorbed. It solves both limitations faced by air vessels. As there is no contact here between air and water, no bacterial spread can happen. Also stays there for a long time and doesn’t get absorbed in water.
Hence, we have learned all about water hammer, definition, meaning, equation, etc.
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