1. What is a water hammer ?
The water hammer phenomenon is also known as hydraulic shock. It is a phenomenon in which the pressure in the pipeline increases suddenly or suddenly decreases. Produced when a fluid (usually a liquid but sometimes also a gas) in motion is forced to stop or change direction suddenly. This phenomenon usually occurs when the valve is suddenly closed at one end of the pipeline system and creates a pipeline pressure wave.
A water hammer occurs when the flow of water is suddenly stopped. At the point the water is blocked will create extreme pressure. It is like dams that release water when floods come because if not released, extreme water pressure will cause the dam to explode.
For steam systems in a plant, a water hammer occurs when the steam trap is not functioning as designed, such as no condensate discharge or reverse installation. Water in the pipe moves at high velocity in the pipe, which quickly leads to the water hammer phenomenon. In addition to the pressure of water, the pipeline must bear the high pressure of steam. It is these things that resonate with the very high risk of steam pipelines bursting.
2. The stages of formation of the hydraulic shock phenomenon
Water hammer is formed in 3 stages :
– Stage 1: The pump is operating normally. The power is suddenly lost, and the pump is still rotating in inertia. The rotation speed of the impeller will decrease, making the flow and head decrease as well. At this time, the movement of the pump and the flow is still in the normal direction.
– Stage 2: Due to sudden power failure, the height of the pressure head continues to decrease. The water head in the return pipeline is reversed if the water head pressure is lower than the calculated pressure in the pipeline. At this time, the impeller continues to rotate, and the back pressure will cause the pump to push up.
This creates a chain of unstable pressures and causes friction and conflict inside the pipeline that interferes with the flow. This is the phenomenon we still call the water hammer phenomenon. At that time, the pressure inside the pipeline increases rapidly, and the return water head will create a dangerous force on the moving impellers, reducing the rotation speed rapidly.
- Stage 3: The rotation of the impeller continues to decrease, and the impeller stops rotating. The back pressure of the water head will affect the impeller and cause the impeller to rotate in the opposite direction, and it will damage the pump. Pump failure usually occurs when a water hammer occurs if a check valve is not installed in front of the pump to prevent water from returning.
3. Harm of water hammer
• When water hammer occurs in the pipeline system. The stop valve is the first affected device. When the pressure increases suddenly, it will affect the valve disc to squeeze. A bit heavier can deform the valve disc or, most severely, crack the valve disc or valve.
• The next effect is on the pipeline system. The sudden increase in pressure exceeding the nominal pressure value of the pipeline will create cracks, breaks, and leaks. In more severe cases, a system explosion may occur.
• Pressure wave due to pressure drop, backflow pressure (surge) can cause significant damage to the system. When vacuum pressure is formed, the system falls into a negative pressure state. Leads to system distortion. In addition, the feedback pressure acts on not only the valves but also the system over and over again, causing hefty damage.
4. Fix the water hammer phenomenon
Water hammer causes accidents and even death. But usually, the damage is limited to the rupture of pipes or ancillary equipment. Therefore, we need to pay attention to avoid greater risks by taking specific measures such as:
• Reduce the pressure of water supply to buildings by installing a central control panel.
• The valve should be closed slowly. Sanitary water supply valves are usually designed as quiet valves. Therefore, the valve can only be approached slowly.
• Use pipelines with high-pressure resistance.
• Good pipeline control (sequence of opening and closing).
• A hydraulic device similar in principle to a shock absorber is called a “Water Hammer Brake”. It can be installed between water pipes and machinery. To absorb shock and stop the impact.
• Reduce branch pipe length.
• Reduce the length of the straight pipe. That is, add a bent pipe, a U-shaped or bent pipe. The water hammer is related to the speed of sound in the fluid, and the bendy coupling reduces the effect of the pressure wave.
• Arrange larger pipes in the main loops. This makes the smaller branch pipes shorter. With a pipe system designed in the form of a ring. Lower velocity flows from both sides of the loop can serve as a branch pipe.
• Install anti-water hammer or hydraulic pressure relief valves for the safe operation of the system.
5. What is a water hammer valve ?
- Water hammer valve, also known as an anti-collision valve, is a type of industrial valve. Its primary function is to resist the water hammer phenomenon. In addition, it also participates in reducing noise as well as vibration of the pipeline system when working. The valve will help avoid the pressure-causing water shock when the one-way valve is closed. In some systems, the anti-water hammer valve also helps to absorb the forces generated by the return liquid when the pump is suddenly turned off.
- Depending on the system's structure, flow rate, and pipe size, users can choose the appropriate size water hammer valve to use and install in many different locations.
6. Structure of water hammer valve :
The anti-collision valve is made up of many simple parts that make up the valve such as:
- The body of the anti-collision valve is cast iron with two ends connected to the pipeline systems in a flange installation style.
- The anti-collision valve cap is a part installed on the valve body made of the same material as the valve body, used to remove when necessary to maintain and repair the valve.
- Anti-collision valve diaphragm or sealing gasket is made of rubber with the task of preventing fluid leakage to the outside.
- Filter part automatically releases water pressure
- Accessories for ball valve with water opening and closing
- Needle valve included
- 2-way Pilot Tube
- Water pressure adjustment screws
- Pressure Gauges
The anti-collision valve works on the simple working principle of opening and closing the valve based on the large and small impact pressure of the fluid on the system when it passes through the valve. Under normal pressure, the anti-collision valve is permanently closed. When the fluid pressure decreases, the force acting on the valve causes the valve to open. When the liquid returns suddenly, tremendous pressure will be exerted on the pipeline system. At this time, the anti-collision valve has opened and reduces the pressure of the fluid flow and passes through another pipe, helping the roadway resist the water hammer phenomenon and ensuring safety for pipeline operation.
The installation of the shockproof valve also needs to be carried out carefully by the engineers who should pay attention to the following:
- Clean the fluid pipeline to remove foreign objects or impurities stuck inside the pipe wall to avoid clogging and affecting the stable operation of the valve.
- Look closely at the arrow on the valve cover and install it correctly in the direction of the hand. That is the direction of the water line.
- For the best effect, it is recommended to install an additional gate valve behind the water hammer valve.
- Flexible opening and closing of 2-way valves to control water flow through the valve.
- Should connect the signal port of the anti-collision valve to the pipeline so that the distance with the anti-collision valve in front of it is about 2 meters.
- Before operating the valve, it is recommended to check the system once and check the connections to ensure a tight seal and no leakage.
- Close the water supply for the water hammer valve.
- For pipes without water, it takes a certain number of days to discharge the gas.
- In the main pipe, there must be no gas, and it must always be filled with water.
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