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Water hammer

Today I learned about “water hammers” also known as hydraulic shocks. This is a phenomenon one can witness every day when opening and closing a tab in any water pipe system. It’s a shock wave that travels through a liquid backwards, when the liquid’s flow was stopped. Most liquids, like water, are incompressible, which means they are unable to adjust their density to absorb a shock wave. Instead the shock wave travels through the liquid with the entire momentum of the mass of the liquid was moving before. Pipe systems have to account for those shock waves by being able to adjust the system pressure to those shock waves which increase the system pressure by magnitudes for a very short period of time only to drop it below the regular pressure directly afterwards. The Joukowsky equation is used to calculate the shock wave of a hydraulic shock and mainly provides 3 parameters to adjust, which are the speed of the shock wave, the speed of the liquid and the time that is taken to stop the flow. The easiest to adjust for you as a person and therefore reducing the amount of “water hammers” in the pipes you handle every day, is the time that you take to stop the liquid, i.e. closing the tab. Do it slow and the waves will be small, even when the design of your pipe system should already have taken care of them.

I came across this while watching stuff on YouTube. I ended up on a video titled “What is a water hammer” by “Practical Engineering” along with their video about “Hydrostatics”. I can highly recommend to watch the video about “Water hammers” because they provide a way more detailed and elaborated explanation than I did here, including some experiments and visualisations. Additionally it might be nice to read the Wikipedia article about water hammers as well, which is always a nice addition.