GEFA Water Hammer GB

Summary

The video explains the phenomenon of water hammer effect, captured through high-speed camera footage. It demonstrates the forces generated when water rapidly hits a valve, with water columns pulling back and creating a vacuum. The slow-motion images reveal the immense pressure and stress, including gasket failure and structural deflection, caused by this rapid force. The video also compares the acceleration and deceleration of water to that of high-speed aircraft, emphasizing the extreme pressure (58.6 bar) that is exerted, equivalent to the weight of a heavy truck. This intense force showcases the destructive potential of water hammer in systems.

Takeaways

• 😀 Water hammer occurs when a valve is closed rapidly, causing a surge of pressure within the system.
• 😀 The high-speed camera footage reveals the water hammer effect, showing how the water column is pulled back and forces are generated.
• 😀 The vacuum pressure generated by water hammer ranges between 0.1 to 0.2 bar, pulling the water column back by 30 cm in just 64 milliseconds.
• 😀 The backflow speed during water hammer is 4.7 m/s or 17 km/h, roughly equivalent to the speed of a cyclist.
• 😀 Water hammer results in visible damage, such as water squirting out of flung gaskets and the stretching of studs in the system.
• 😀 The force generated by water hammer can be compared to the pressure exerted by a 3-ton truck resting on a 50 cm² surface.
• 😀 The deceleration of the water is extremely rapid, with acceleration reaching 586 m/s² or 59.7 G during the stop.
• 😀 The force exerted during the deceleration phase is 29,300 Newtons, which is enough to cause significant pressure on the system components.
• 😀 The rapid deceleration of water in water hammer is far greater than the deceleration experienced in high-speed vehicle crashes or aircraft accidents.
• 😀 Understanding water hammer and its forces is crucial for engineers to prevent potential damage to pipes and valves in industrial systems.

Q & A

What is water hammer and what causes it?

Water hammer is a hydraulic phenomenon that occurs when a valve is rapidly closed, causing the moving water to decelerate abruptly and generate high pressure waves within the pipe system.

How are the effects of water hammer captured in the video?

The effects of water hammer are captured using a high-speed camera running at 10,000 frames per second. This allows for the observation of phenomena that are not visible to the naked eye, such as the vacuum generation and water column retraction.

What happens to the water column during water hammer?

During water hammer, the water column is pulled back due to the vacuum generated by the rapid deceleration of the water flow. This creates a backflow that can travel a distance of 30 cm in just 64 milliseconds.

How fast does the water travel during the backflow in a water hammer event?

The backflow speed of the water during water hammer is approximately 4.7 m/s, or 17 km/h, which is roughly the speed of a cyclist.

What structural effects are observed on the valve components during water hammer?

During water hammer, the structural components of the valve experience visible deformations. For example, the gasket is forced out, and the valve studs are stretched. The entire construction shows a deflection of up to 15 mm.

What is the vacuum pressure generated during water hammer?

The vacuum pressure generated during water hammer ranges from 0.1 to 0.2 bar, which causes the water column to retract and the valve components to experience mechanical stress.

How does the deceleration of the water during water hammer compare to that in a pursuit plane?

The deceleration of water during water hammer can reach up to 586 m/s² (or 59.7 G), which is far higher than the typical deceleration in a pursuit plane, which can reach 10 G. In extreme accidents, deceleration can reach up to 50 G in 8 milliseconds.

What is the equivalent force on a valve disc during water hammer?

During water hammer, the force on a valve disc can reach 29,300 Newtons on a 50 cm² surface area, equivalent to the pressure exerted by a 3-ton truck resting on that surface.

What speed does the water reach during the backflow in water hammer, and how does it compare to common objects?

The backflow speed of the water is about 17 km/h (4.7 m/s), which is comparable to the speed of a cyclist. This shows that even small amounts of water in motion can generate significant forces.

Why are high-speed camera recordings necessary to study water hammer?

High-speed camera recordings are necessary because the effects of water hammer, such as vacuum formation and water column retraction, occur too quickly to be observed by the naked eye. The footage helps engineers understand the precise dynamics and forces involved.