The 2 most common causes of water hammers are from fast closing valves or from slugs which form during 2 phase flow.
Water Hammer – Fast Closing Valves
Water hammer is a pressure surge or wave caused when a fluid (usually a liquid but sometimes also a gas) in motion is forced to stop or change direction suddenly. A water hammer commonly occurs when a valve closes suddenly at the end of a piping system.
The occurrence of a water hammer can be detected by the noise it makes. As the water is forced to stop suddenly, there is a sudden rise in pressure as the water is suddenly stopped at the site of the sudden valve closure. The piping then experiences a pressure wave that travels back through the piping system.
Figure 1 – Water Hammer from Fast Closing Valve
Water Hammer – Slug
In a line where steam is subject to loss of energy (such as traveling away from a boiler), the steam can condense inside the pipework. The rate of condensate formation can be particularly high during startups. When condensate forms, there is both gas and liquid in the line with very different flow velocity (steam is much higher than that of the condensate). The more rapid flow of steam over the condensate causes waves in the condensate. This may lead to a situation where the condensate ends up encompassing an entire cross-section of the piping. When this happens, a pocket of steam is trapped within condensate and will cause a mass of water (called a slug) to move at the flow rate of steam. The slug can carry significant force due to the mass of the liquid traveling at the rate of steam. When the slug hits a bend, the kinetic energy of the slug will be suddenly converted into pressure energy which will create a shock wave in the line.
Figure 2 – Water Hammer from Slug Formation
PT&P Product Solutions
PT&P has been assisting customers for many years with water hammer issues.
Our Product Solutions for water hammers include:
- Snubbers – snubbers are specially designed for handling transient events such as a water hammer. A snubber allows free movement except when the piping suddenly accelerates. Upon sudden acceleration, the snubber becomes rigid support (it operates similar to seat belt).
- Hold-Downs – PT&P hold-downs can be designed to withstand the forces produced by a water hammer.
- Custom Designed Supports – PT&P can custom design supports to support water hammer forces.
PT&P Service Solutions
Water Hammer Assessment – PT&P can assess lines experiencing water hammers and develop solutions to either address root cause issues or allow the line to better withstand the forces from a water hammer in order to minimize short and long term damage from ongoing water hammer issues.