civil engineering Civil engineering is a professional engineering discipline that deals with the design, construction, and maintenance of the physical and naturally built environment, including public works such as roads, bridges, canals, dams, airports, sewage ...

, a transient is used to refer to any pressure wave that is short lived (i.e. not static pressure or pressure differential due to friction/minor loss in flow). The most common occurrence of this is called

water hammer Hydraulic shock (colloquial: water hammer; fluid hammer) is a pressure surge or wave caused when a fluid in motion, usually a liquid but sometimes also a gas is forced to stop or change direction suddenly; a momentum change. This phenomenon com ...

. In a pipe network, when a valve or pump is suddenly shut off, the water flowing in an adjacent pipe is suddenly forced to stop. A region of high pressure builds up immediately behind said valve or pump and a region of low pressure forms in front of it. The momentum of the water is suddenly transferred into the fitting and

Newton's Third Law Newton's laws of motion are three basic laws of classical mechanics that describe the relationship between the motion of an object and the forces acting on it. These laws can be paraphrased as follows: # A body remains at rest, or in motion ...

kicks in forming a high-pressure region of water as it all "piles up" in the pipe. This high pressure region then travels back along the pipe in the form of a wave. The border of the high-pressure zone is referred to as a pressure wave, or transient (which is apt as the general definition of a transient is something that only exists for a short period of time). Transients are often misunderstood and not accounted for in the design of water distribution systems and are often the cause of (or a contributing factor to) hydraulic element failures (i.e. pipe breaks, pump/valve failures, etc.).

External links

Journal of Applied Fluid Transients (JAFT)
Hydraulic engineering {{civil-engineering-stub