Repairing or replacing damaged pipeline components and equipment can involve steep costs. It also causes pipe wall cracks and deformation of piping support systems. Water hammer causes leaks at the joints in the system. The pressure spikes can easily exceed 5 to 10 times the working pressure of the system upon impact, thereby placing a great deal of stress on the system. ![]() Water hammer also seriously damages pipelines, pipe joints, gaskets and all the other components of the system (flow meters, pressure gauges, etc.). Repeated occurrences of water hammer aren’t just an annoyance, however. This sometimes-deafening noise can be a source of great distress and concern, especially if people are working close by. This is the sound of the pressure shock wave hitting a closed valve, joint or other blockage at high force. A common sign is a loud banging or hammering sound emanating from the pipes, especially after a water pressure source is shut off quickly. The consequences of water hammer can range from mild to severe. If the flow is stopped in less than a half second (which might be the closing speed of the valve), then a pressure spike over 100 psi greater than the system operating pressure can be generated. When the flow is quickly brought to a halt by a fast-closing valve, the effect is equivalent to that of an 835-pound hammer slamming into a barrier. For example, consider 100 gallons of water flowing in a 2-inch pipe at a velocity of 10 feet per second. The actual force of water hammer depends on the flow rate of fluid when it is stopped and the length of time over which that flow is stopped. It is possible to calculate the magnitude of water hammer pressure spikes based on detailed knowledge of the piping system and the media transported. Silent check valves can be extremely effective in reducing and sometimes eliminating water hammer. Multiple pumps feeding into a common header, as in cooling tower applications or mine dewatering, either need to be shut down slowly, or they need to have in-line silent check valves installed immediately after the pump. The other most common cause of water hammer is sudden pump shutdown. More on valve closure time calculations is included later in this article. For example, emergency shutdown valves need to close quickly, so other solutions may be necessary for these types of applications. This works in many cases but not all of them. A simple solution is to close those automated quarter-turn valves more slowly. Sudden valve closure is most often associated with quarter-turn types of valves and more specifically, automated quarter-turn valves. When a valve suddenly closes or a pump suddenly stops, the fluid in the piping system downstream of the valve or pump will be elastically stretched until the momentum of the fluid is arrested. The momentum of the fluid traveling in its forward direction will work to keep the fluid moving in that direction. As Sir Isaac Newton observed, an object in motion tends to stay in motion unless acted upon by another force. Hydraulic shock is, in fact, the momentary rise in fluid pressure in a piping system when the fluid is suddenly stopped. The most common cause of water hammer is either a valve closing too quickly or a pump shutting down suddenly. The first is to study causes, consequences and solutions. Certain steps can prevent or mitigate water hammer. Localized, abrupt pressure drops are an annoyance at the least and a serious problem at the most. In the worst case, this could do serious damage to other piping system components. This leads to leaks that, in the best case, undermine the efficiency of the system. The resulting shock can damage the alignment of the disc so that it no longer makes full, 360-degree contact with the seat. If the reverse flow is forceful, as in the case of a vertical line with normal flow upwards, the disc is likely to slam with a great deal of force. ![]() These check valves are prone to slamming because they rely on reversing flow and backpressure to push the disc back onto the seat so that the valve closes. Certain valves, such as swing check valves, tilting disc checks and double door check valves also can contribute to water hammer problems. Water hammer can result from improper valve selection, improper valve location and sometimes poor maintenance practices.
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