The rotameter is primarily used to indicate what?

The rotameter is a type of flow meter used to measure the flow rate of liquids or gases. It operates on the principle of variable area flow measurement, where a float within a tapered tube rises or falls depending on the flow rate. The height of the float indicates the flow rate on a calibrated scale, typically expressed in volumetric terms.

In the context of the choices provided, the correct answer focuses on the use of the rotameter for measuring feed rates. Specifically, it is capable of indicating the feed rate in terms of volume flow, such as gallons per minute or liters per minute. This makes it an important instrument in many water and wastewater applications, where understanding the volume of fluid moving through a system is crucial for operations and efficiency.

The option regarding feed rate in pounds per day can sometimes confuse users, as it assumes the user would want a mass flow measurement, which is often derived from volumetric measurements using density. However, a rotameter is primarily calibrated and read based on volumetric flow, not mass. Therefore, while a rotameter can provide flow information that might be converted to mass flow rates under certain conditions, its primary function is not to directly measure or indicate mass flow rates but rather the volumetric flow through