Valves that pass fluids when closed (e.g. a gas or liquid) can cause process problems, waste energy and have serious safety implications.

For example, valve stems can leak gas and potentially pollute the atmosphere and increase safety hazards. Pressure relief valves lifting at the wrong pressure (or not lifting at all) can also have similar results.

Ultrasound is a completely non-invasive technology, and can be used to listen to internal valve activity (e.g. leakage and blockage). Ultrasonic instruments can also be used to check a valve whilst in operation.

Properly seated valves are quiet, but a leaking valve produces a turbulent flow as the gas or liquid moves from high to low pressure. Generally speaking, a valve that is tightly shut off should not add to the background level of ultrasound. A passing valve, however, will sound different and produce a higher reading on the instrument.

Valve chatter (e.g. on compressors or engines) can often be analysed further in PC software, and valve stems can be quickly tested for leaks to atmosphere. Cavitation, a phenomenon that produces noise and vibration as well as pipe and valve damage, can be identified early so as to reduce or eliminate its effects.