Steam

Steam becomes trapped in water...

http://www.kirsner.org/pages/articlesAlt.html

Er, actually, that's called "priming".

As I understand water hammer is the noise of water (or other fluids), and and vibration of water lines up and down the line, in response to opening or closing a valve.

It is caused by a sudden velocity change in the water. Such as suddenly closing (or opening) a valve, stopping a pump, etc.

Water Hammer is caused by the momentum of the water moving in the lines suddenly transferring to other forms of energy. Because the water is suddently stopped, the energy is expressed as pressure waves that move fast up and down the water line. Often these waves will put physical stresses on the pipe mounting or even the pipe itself. If severe enough, the pressure wave will exceed the bursting pressure of the pipe.

Preventing water hammer is done in two ways. Either preventing it occuring by controlling the rate of acceleration or deceleration of the water (slowly opening and shutting valves), or by installing water hammer arresters, which basically absorb the energy of the pressure wave.

Hope this helps.

Anthony

The terms "water hammer" or "liquid hammer" includes both of the sources described in the previous Good Answers. Some other terms you might examine include "vapor propelled acceleration", "sudden deceleration", "condensation collapse", etc. These conditions also pertain to refrigeration systems, and any other systems involving change of phase.

It's a good topic to enter into the search facility in Wikipedia. After Caps Lock has been turned off, of course.

My understanding of the meaning of the term "water hammering" or "water hammer" is a little different than the above - perhaps from an earlier era of technology. It is a process that occurs in enclosed, heated water systems such as steam producing boilers, or hot water producing boilers that have specific locations within the system that have significantly lower water temperatures, such as feed water inputs where a significant volume of colder water can collect, or heating pipes carrying steam that have condensate not drained completely and partially cooled from an earlier cycle. The hammering is a sudden movement of the colder water caused by mixing of the colder water with steam in a positive feedback action in which the movement of the colder water creates even greater faster mixing of the steam and water, thus accelerating the moving colder water. The steam condenses rapidly, making a partial vacuum which pulls the colder water into the steam. When the steam is gone, being all condensed back into water, the rapidly moving water has no place to go, and slams to a stop. The sound of boiling water in a pot is a miniature version of the same process, with steam bubbles collapsing into the water. That is why the sound of cold water in a pot on a hot stove is different than the sound of the pot when it is nearly or fully boiling, since the temperature differences are greater in the cold water pot. When a boiler system is set up properly, there should be no water hammer, since there are significant destructive forces involved which can break the pipes, especially old ones. Buildup of salt deposits (lime, etc) can restrict water flow and partially insulate the heating area, both things that can cause water hammer. Improper original layout or modifications to older systems can also create water hammer. Information on eliminating water hammer is available if you look for it.

Water hammer is the hammering of water in the steam lines due to accumulation of condensate in the lines and then sudden flow or stopage of flow towards the opening or closing a valve.

The accumulation of condensate is caused due to poor draining system of the steam lines during heating up or due to poor insulation of steam lines or both.

Because the water in the lines gains momentum with velocity of steam, which causes heavy blow due to suddently stopped opening. Often these waves will put physical stresses on the pipelines supports, mounting or even the pipe itself. It may become severe enough to damage the pipe line.

Preventing water hammer is done in following ways.

Proper design of loops and drain system of steam line,

Proper draining of condensate through steam traps,

Improving insulation of the lines,

Proper heating of line before ful flow of steam,

I hope this will help.

Why water hammer in steam pipe lines ,water hammer in condensate pipes and how to avoid water hammer in steam system.

your answer is here http://www.bellgossett.com/Press/BG-good.asp

Ohhh , I'm sorry

I've mistaked , here is the right link

Preventing Water Hammer in Steam Systems | Xylem - Residential ...