Water Hammer
Q1
Q1
A) The sudden closure of valve at the end of a pipeline cause sudden change in the water velocity which in turn creates a phenomenon called water hammer. The water in motion is forced to stop or change direction suddenly (momentum change) and a pressure wave propagates in the pipe. It 's also called hydraulic shock.
The effect of this event can be effectively multiplied many times by the geometry of a piping system if the pressure wave is allowed to reflect, or bounce, back and forth within the system. A single valve closure can generate multiple positive and negative pressure surges, for seconds afterwards.
This pressure wave can cause major problems, from noise and vibration to pipe collapse. It is possible to reduce the effects of the water hammer pulses with accumulators and other features.
Here is a brief description of the Pressure and velocity waves in a single-conduit, frictionless pipeline following its sudden closure. The areas of steady-state pressure head are shaded medium dark, those of increased pressure dark, and those of reduced pressure light. The expansion and contraction of the pipeline as a result of rising and falling pressure levels, respectively, are shown:
1. For t = 0, the pressure profile is steady, which is shown by the pressure head curve running horizontally because of the assumed lack of friction. Under steady-state conditions, the flow velocity is 0.
2. The sudden closure of the gate valve at the downstream end of the pipeline causes a pulse of high pressure _h; and the pipe wall is stretched. The pressure wave generated runs in the opposite direction to the steady-state direction of the flow at the speed of sound and is accompanied by a reduction of the flow velocity to v = 0 in the high pressure zone. The process takes place in a period of time 0 < t < 1/2 Tr, where Tr is the amount of time needed by the pressure wave to travel up and down the entire length of the pipeline. The important
Q1
A) The sudden closure of valve at the end of a pipeline cause sudden change in the water velocity which in turn creates a phenomenon called water hammer. The water in motion is forced to stop or change direction suddenly (momentum change) and a pressure wave propagates in the pipe. It 's also called hydraulic shock.
The effect of this event can be effectively multiplied many times by the geometry of a piping system if the pressure wave is allowed to reflect, or bounce, back and forth within the system. A single valve closure can generate multiple positive and negative pressure surges, for seconds afterwards.
This pressure wave can cause major problems, from noise and vibration to pipe collapse. It is possible to reduce the effects of the water hammer pulses with accumulators and other features.
Here is a brief description of the Pressure and velocity waves in a single-conduit, frictionless pipeline following its sudden closure. The areas of steady-state pressure head are shaded medium dark, those of increased pressure dark, and those of reduced pressure light. The expansion and contraction of the pipeline as a result of rising and falling pressure levels, respectively, are shown:
1. For t = 0, the pressure profile is steady, which is shown by the pressure head curve running horizontally because of the assumed lack of friction. Under steady-state conditions, the flow velocity is 0.
2. The sudden closure of the gate valve at the downstream end of the pipeline causes a pulse of high pressure _h; and the pipe wall is stretched. The pressure wave generated runs in the opposite direction to the steady-state direction of the flow at the speed of sound and is accompanied by a reduction of the flow velocity to v = 0 in the high pressure zone. The process takes place in a period of time 0 < t < 1/2 Tr, where Tr is the amount of time needed by the pressure wave to travel up and down the entire length of the pipeline. The important
References: 1. Keech, Andrew. The Engineering Significance of Pressure Surges. Hydraulics Analysis LTD. HORSFORD, LEEDS, ENGLAND. 2. The Society of International Gas Tanker and Terminal Operators LTD (SIGTTO). Guidelines for the Alleviation of Excessive Surge Pressures in ESD. Witherby & Co. LTD. LONDON. EC1, ENGLAND, 1987. 3. Waters, Gary Z. Analysis and Control of Unsteady Flow in Pipelines. Butterworths Publishers, 1984. 4. Pipe Line Rules of Thumb Handbook. Gulf Publishing Company, 1993.