Final answer:
A pressure test is performed by pressurizing air in a closed vessel to detect leaks. Manometers are used to measure the pressure during the test, and mercury is often used in these devices due to its high density.
Step-by-step explanation:
In the context of the test being described, the blank should be filled with the term pressure test. During a pressure test, air is pressurized in a closed vessel to detect leaks. This is a common procedure in various engineering fields to ensure that components such as valves, pipelines, and containers can withstand their operational pressures without leakage. The pressure within the vessel is increased above its anticipated operating pressure to ensure safety and integrity. Manometers, such as closed-end or open-end types, are instruments used to measure pressure, and in certain applications, different fluids like mercury may be used due to their high density, thereby offering more accurate pressure readings.