Water Hammer Pressure Increase Formula |
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\( WH_{pi} \;=\; \dfrac{ \rho \cdot v \cdot \Delta v }{ 2 \cdot g }\) (Water Hammer Pressure Increase) \( \rho \;=\; \dfrac{ 2 \cdot g \cdot WH_{pi} }{ v \cdot \Delta v }\) \( v \;=\; \dfrac{ 2 \cdot g \cdot WH_{pi} }{ \rho \cdot \Delta v }\) \( \Delta v \;=\; \dfrac{ 2 \cdot g \cdot WH_{pi} }{ \rho \cdot v }\) \( g \;=\; \dfrac{ \rho \cdot v \cdot \Delta v }{ 2 \cdot WH_{pi} }\) |
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| Symbol | English | Metric |
| \( WH_{pi} \) = Water Hammer Pressure Increase (psi) | \(lbf\;/\;in^2\) | \(Ps\) |
| \( \rho \) (Greek symbol rho) = Fluid Density | \(lbm\;/\;ft^3\) | \(kg\;/\;m^3\) |
| \( v \) = Fluid Velocity | \(ft\;/\;sec\) | \(m\;/\;s\) |
| \( \Delta v \) = Fluid Velocity Change | \(ft\;/\;sec\) | \(m\;/\;s\) |
| \( g \) = Gravitational Acceleration | \(ft\;/\;sec^2\) | \(m\;/\;s^2\) |
Water hammer pressure increase, also called hydraulic shock, is a sudden and significant rise in pressure within a pipeline. This occurs when a fluid in motion, such as water, is abruptly forced to stop or change direction. The momentum of the moving fluid is suddenly converted into a pressure wave that propagates through the pipe. A common cause is the rapid closure of a valve, which halts the flow of water and creates a pressure surge that travels back and forth within the system, often manifesting as a loud banging or hammering noise.
The magnitude of the pressure increase depends on several factors, including the fluid's velocity, the pipe's length, the speed at which the flow is stopped, and the elasticity of the fluid and the pipe walls. This pressure surge can be several times greater than the normal operating pressure of the system and can pose a significant risk to the integrity of the pipes and connected equipment.
