Which rotameter flow indicator is read in the middle of the dial?

Which rotameter flow indicator is read in the middle of the dial?

• A. Bobbin
• B. H float
• C. Ball float
• D. Skirted float

Answer: (C)

In a rotameter, flow is determined by how high the float rises in a tapered tube—the higher the float, the greater the flow. Reading the flow depends on the float’s shape because different shapes present the scale marks at different parts of the float. A ball float is spherical, so its center line sits at a stable, unambiguous reference point. The scale on a ball-float rotameter is calibrated so that the flow rate corresponds to the middle of the ball. That means you read the value at the ball’s midpoint—the middle of the dial—to get the accurate flow. Other float shapes are read at different reference points along the float (top, bottom, or edges) due to their geometry, which is why they’re read elsewhere on the float.

In a rotameter, flow is determined by how high the float rises in a tapered tube—the higher the float, the greater the flow. Reading the flow depends on the float’s shape because different shapes present the scale marks at different parts of the float.

A ball float is spherical, so its center line sits at a stable, unambiguous reference point. The scale on a ball-float rotameter is calibrated so that the flow rate corresponds to the middle of the ball. That means you read the value at the ball’s midpoint—the middle of the dial—to get the accurate flow. Other float shapes are read at different reference points along the float (top, bottom, or edges) due to their geometry, which is why they’re read elsewhere on the float.