Which of the following is NOT a flow measuring device?

A manometer is a device used to measure the pressure of a fluid in a system, rather than measuring flow. It typically consists of a tube filled with a liquid, where the difference in the height of the liquid column indicates the pressure. This measurement is crucial for understanding the conditions within a system, but it does not provide direct information about the flow rate of a fluid.

In contrast, the other options—V notch weirs, magnetic flow meters, and Parshall flumes—are specifically designed to measure flow. V notch weirs measure flow over a triangular notch, using the height of the water flowing over the notch to determine the flow rate. Magnetic flow meters work on the principle of electromagnetic induction to measure the velocity of conductive fluids, allowing for precise flow measurement. Parshall flumes are open channel devices that use a specific shape to create a relationship between the flow rate and the water level, allowing for accurate flow measurement.

Understanding the distinction between devices that measure flow and those that gauge pressure is fundamental in wastewater treatment and management.