Texas Commission on Environmental Quality (TCEQ). Class C Water License Exam

What issue can arise in the distribution system when a valve or hydrant is opened or closed too quickly?

1. Water hammer

2. Pressure surge

3. Vacuum loss

4. Cavitation

The correct answer is: Water hammer

When a valve or hydrant is opened or closed too quickly, the phenomenon that most commonly arises is water hammer. Water hammer occurs due to the sudden change in water flow, which generates a shock wave within the pipes. This shock wave can lead to loud banging noises and can cause physical stress on the piping system, potentially resulting in pipe damage or leaks. The abrupt change in movement creates rapid pressure changes, contributing to this effect. In practice, the consequences of water hammer can include not just noise, but also damage to valves, fittings, and other components of the water distribution system due to the force exerted by these pressure surges. While pressure surge, vacuum loss, and cavitation are all important concepts related to changes in pressure or flow within water systems, they are not the primary issue directly associated with the quick opening or closing of valves and hydrants. Pressure surges can contribute to similar outcomes as water hammer but do not specifically describe the immediate effect of rapid changes. Vacuum loss pertains to a situation where the pressure in the system drops below atmospheric pressure, leading to potential negative pressure issues. Cavitation involves the formation of vapor bubbles in a fluid, which can occur under specific conditions of pressure and flow rather than directly as a result of