To measure vacuum on a fan inlet, what instrument is used?

The appropriate instrument for measuring vacuum on a fan inlet is a pipe tube manometer. This device is designed to measure differential pressure and is especially suited for applications where low-pressure readings are taken, such as vacuum measurements. It operates based on the principle of balancing a column of liquid against the pressure being measured.

In vacuum applications, the pipe tube manometer can provide accurate readings by indicating the height difference of a liquid column, which correlates to the level of vacuum created. This makes it particularly effective for assessing the conditions in a fan inlet, where the operation creates a negative pressure relative to the atmospheric pressure.

While other instruments like digital manometers and Bourdon gauges can measure pressure, they may not be as effective or suitable for low-pressure vacuum measurements. Digital manometers might not have the sensitivity needed at extremely low pressure, and Bourdon gauges typically measure positive pressures instead. Pressure gauges, on the other hand, are used to measure the pressure of gases and liquids in a specified range, often not designed for vacuum applications specifically. Hence, a pipe tube manometer is the optimal choice for measuring vacuum in this scenario.