Describe the causes of water hammer in a potable water system and the methods used to prevent it.

Water hammer in a potable water system is a pressure surge or wave caused by the sudden stop or change in direction of water flow. This sudden change in momentum creates a shock wave that travels through the pipes, causing a banging or hammering noise. The primary cause of water hammer is the rapid closure of valves, especially quick-closing valves such as solenoid valves or ball valves. When a valve is suddenly closed, the water flowing behind it is abruptly stopped, creating a pressure wave that travels back up the pipe. This pressure wave can be several times higher than the normal operating pressure, potentially damaging pipes, fittings, and equipment. Other causes of water hammer include pump starts and stops, and the rapid filling or emptying of pipes. Several methods are used to prevent water hammer. Water hammer arrestors are devices installed in the piping system that absorb the energy of the pressure wave. They typically consist of an air chamber or a spring-loaded piston that compresses when the pressure wave arrives, dissipating the energy. Slow-closing valves can be used to reduce the rate at which the water flow is stopped. These valves gradually close over a period of several seconds, minimizing the pressure surge. Air chambers, also known as air cushions, can be installed in the piping system to provide a buffer for the pressure wave. These chambers are partially filled with air, which compresses when the pressure wave arrives, absorbing the energy. Properly sizing the pipes can also help to reduce water hammer. Larger pipes have a lower flow velocity, which reduces the magnitude of the pressure surge when the flow is stopped. Finally, proper pipe support can help to reduce the noise and vibration associated with water hammer. Securing the pipes to prevent them from moving can minimize the banging and hammering noise.