A negative gauge pressure in fluid indicates what?

• A. Negative gauge pressures are not possible
• B. A vacuum pressure exists in the measured fluid
• C. The gauge pressure is equal to zero pressure
• D. The pressure is higher than the absolute vacuum pressure

Answer: (B)

A negative gauge pressure in a fluid indicates that the pressure of the fluid is below the atmospheric pressure. This situation is typically associated with a vacuum condition. In practical terms, gauge pressure measures the pressure of a fluid relative to the atmospheric pressure; therefore, when the gauge reads a negative value, it signifies that the fluid’s pressure is less than atmospheric, indicating that it is suction or vacuum pressure. Such conditions are common in scenarios where fluids are drawn through pipes, and they help in maintaining flow without drawing in air, which could introduce contaminants or cause operational issues.

In contrast, negative gauge pressures are conceptually possible and represent a valid physical condition rather than being an impossible measurement. A measurement of zero gauge pressure is indicative of a pressure that exactly matches atmospheric pressure, while pressure readings above zero would indicate a fluid pressure that exceeds atmospheric levels. Thus, while options addressing these conditions may exist, they do not accurately represent the condition of negative gauge pressure as vacuum pressure does.