In engineering, “shock” is defined as a phenomenon that happens when matter is subject to extreme rates of force with respect to time. This is probably one of those engineering concepts that most of us understand without a scientific dissertation. In plumbing engineering, one of the most common forms of shock is water hammer: A phenomenon caused by water moving at a high velocity that stops suddenly. Not only does water hammer cause a problem because of the noise it makes but it can cause piping and fittings to fail prematurely as well.
We should all be familiar with the concept of what happens when something that has momentum gets stopped suddenly. A good example is when you are walking down a busy sidewalk and someone stops in front of you suddenly to check their phone. In the case of water hammer, it happens when a valve is closed suddenly, and this is usually the case with valves that are electrically controlled. This is the case with solenoid valves, which operate when electricity is applied to a winding and pulls in armature. Plumbing codes may require us to design systems with devices that absorb pressure resulting from the quick-closing of valves. The first question then becomes: “What defines a quick-closing valve?”