3-1-3 Measures for water hammer problem

Summary

This video discusses the problem of water hammer in pipelines and various measures to prevent its damaging effects. Water hammer occurs due to sudden changes in water flow, particularly when pumps stop unexpectedly. The video explores preventive solutions such as surge tanks, air chambers, flywheels, slow-closing check valves, and air valves. These technologies mitigate negative pressure and pressure surges in water systems. Examples, including the Toyota Water Conveyance Pipeline, highlight practical implementations of these solutions. The video emphasizes the importance of considering topography, pipeline specifications, and system needs in designing effective water hammer prevention strategies.

Takeaways

• 😀 Water hammer is a phenomenon that can cause significant damage to pipelines and pumps, and requires measures for prevention.
• 😀 Water hammer effects are less likely when the landscape is gentle near the pump and receiving tank but more likely when there are abrupt height changes, such as mountainous sections.
• 😀 Negative pressure generation during sudden pump stops is a key concern, and it can be predicted by drawing the minimum water pressure gradient line.
• 😀 Water column separation is likely to occur when negative pressure is under 7 meters, which is the threshold for pipeline damage due to negative pressure.
• 😀 If negative pressure exceeds 7 meters, additional measures are needed to prevent water hammer effects.
• 😀 Surge tanks are installed on large water transmission pipelines to mitigate negative pressure effects caused by sudden pump stops.
• 😀 Surge tanks absorb water from the pipeline and supply it back when pressure rises after negative pressure occurs.
• 😀 Conventional surge tanks require significant height and space, making them difficult to construct; thus, one-way surge tanks are used for efficiency.
• 😀 Air chambers are used in smaller systems and can handle both negative pressure generation and pressure rising after negative pressure occurs.
• 😀 Flywheels mitigate sudden pump stops and negative pressure regeneration by using the inertia force during power failures.
• 😀 Slow closing check valves reduce pressure rising in the pipeline after negative pressure generation and can be installed as part of water hammer prevention strategies.

Q & A

What is water hammer, and why is it a concern for pipelines and pumps?

Water hammer is a shockwave that occurs in pipelines when there is a sudden change in water flow, such as when a pump is turned off quickly. It can cause severe damage to pipelines and pumps due to the high pressure from the shockwave.

How does the topography of the landscape influence the occurrence of water hammer?

The landscape's topography affects water hammer risk. When the landscape is relatively flat near the pump and gradually rises towards the receiving tank, water hammer is less likely. However, if the water level rises abruptly from the pump or if there is a mountainous section along the pipeline, it becomes more susceptible to water hammer.

What is negative pressure, and how does it relate to water hammer?

Negative pressure occurs when the water pressure drops below the atmospheric pressure, often due to a sudden stop in the pump. This can lead to water column separation, which is a key factor in the occurrence of water hammer.

What is the minimum water pressure gradient line, and why is it important in preventing negative pressure?

The minimum water pressure gradient line is calculated to predict the likelihood of negative pressure occurring along the pipeline. It helps determine if additional measures are needed to prevent the harmful effects of negative pressure, such as water column separation.

At what negative pressure threshold does water column separation become a risk?

Water column separation becomes a risk when the negative pressure exceeds 7 meters, which is the threshold where water vapor pressure plus a safety ratio for pipes with diameters of 500 mm or less can cause separation.

What role do surge tanks play in preventing water hammer?

Surge tanks are used to absorb the effects of negative pressure and prevent water hammer. They supply water to the pipeline when negative pressure occurs and absorb excess water during pressure rising. They are especially useful for large-size water transmission pipelines.

Why are one-way surge tanks preferred for certain water conveyance systems?

One-way surge tanks are used because they are simpler to construct and can effectively handle the prevention of negative pressure generation without the need for large tanks that would be required for traditional surge tanks.

What are air chambers, and how do they help manage water hammer?

Air chambers are smaller, more affordable devices used to manage both negative pressure generation and pressure rising after it occurs. They use compressed air to supply water to the pipeline during negative pressure and help balance pressure changes.

How do flywheels contribute to preventing water hammer effects?

Flywheels are installed on the pump’s rotation axis to mitigate sudden pump stops. Their inertia helps prevent the rapid pressure changes that lead to negative pressure and water hammer, especially during power failures.

What is the function of slow-closing check valves in reducing pressure rise in pipelines?

Slow-closing check valves reduce the pressure surge that occurs after negative pressure by gradually closing, which prevents water from rapidly flowing back into the system and causing pressure spikes.