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Water Hammer: A look at the cause and effect

Water hammer is a hydraulic phenomenon that occurs when flowing water is abruptly stopped by a block in its path. Since water molecules have very limited compression capability, a sudden stop forces the water to move in the opposite direction, which is again slammed forward by incoming water and so on. This repeated banging of water onto itself causes a shock wave so strong that it can cause significant damage to pipelines and other linked equipment.

Water hammer can be caused by either the starting/stopping of a pump, or sudden closing of a valve, or pump power failure, or even by improperly operating/incorporating surge protection devices.

Reverse flow causes Water Hammer

Pressure spikes due to water hammer can exceed 5 to 10 times the normal working pressure. This force from water pressure depends on two key factors: flow rate of the fluid, and the length of time over which the flow is stopped. For example, a fast closing valve can result in a force equal to that of an 835 lb hammer via 100 gallons of water flowing through a 2” pipe at 10 feet/second. (Source: Understanding Water Hammer by DFT Valves).

Figure 1: Source: http://www.chengfluid.com/flow_problems/water_hammer
Figure 1: Source: http://www.chengfluid.com/flow_problems/water_hammer

Due to this sudden increase in pressure, several components of the system get impacted. Water hammer can significantly deform and damage pipelines and pipe joints. The sudden pressure differential has been known to crack and burst pipes resulting in expensive repairs and spill damage.

Valves used for managing water flow, when affected by water hammer, can fail completely causing severe damage due to backflow or overflow. Valve failure can also result in collateral damage of other linked equipment such as pressure gauges, flow meters, pumps, boilers, turbines etc.

Further, sudden pressure spikes can lead to blown gaskets and ruptured pipes which can cause serious injury to anyone standing close by. The severity of such damage in an industrial setting can be devastating.

Several solutions exist to keep hydraulic pressure under control. Some of these involve the installation of:

  • Water hammer arrestors,
  • Surge tanks,
  • Pressure vessels,
  • Check valves,
  • Slow closing valves, and/or
  • Air chambers.

Additionally, it is important that companies design systems that optimize valve locations enabling efficient management of pressure fluctuations. Finally, operating personnel need to be adequately trained to ensure that damage due to manual error can be avoided.

By Saumya Garg