Which of the following terms refer to excessive internal pressure, which may be several times the normal operating pressure and can seriously damage hydropneumatic tanks, valves, and the piping network:

• A. Air charge
• B. Flow rate pressure
• C. Water hammer
• D. Hydraulic charge

Answer: (C)

Water hammer is the sudden pressure surge that occurs when a moving column of water is forced to stop or change speed quickly, such as when a valve closes rapidly. That momentum creates a shock wave that travels through the piping and can push pressures well above the normal operating level. In a hydropneumatic system, this surge can compress the air cushion and push the system pressure far beyond its design, leading to serious damage to tanks, valves, and piping. This is why controlling valve closure speed, properly sizing pipes, and using surge protection or appropriate air precharge are crucial. The other terms don’t describe this transient pressure spike: air charge is just the precharge in the tank, flow rate pressure isn’t the standard term for a surge, and hydraulic charge isn’t the recognized phenomenon here.