Which term describes large amplitude pressure waves in piping systems that can cause substantial mechanical damage and may be mitigated with arrestors?

• A. Pressure Drop
• B. Water Hammer
• C. Flow Noise
• D. Thermal Shock

Answer: (B)

Transient pressure surges in piping arise when flow is interrupted or valve closures happen too quickly. The moving fluid has momentum and cannot stop instantly, so it creates a high-pressure wave that races through the pipe. This water hammer can push peak pressures well above normal operating levels, causing pipes to bang, joints to fail, and other mechanical damage. Arrestors provide a cushion by using a compressible or energy-absorbing medium to dampen those waves, cutting the peak pressure and protecting the system.

Pressure Drop is about the steady loss of pressure due to friction and elevation changes along the line, not a rapid, damaging surge. Flow Noise is the audible result of turbulence or irregular flow, not the transient surge itself. Thermal Shock involves stress from rapid temperature changes causing expansion or contraction of materials, which is a different failure mode.