Flow metering – device capable of measuring the largest flow rate Among the listed primary elements/meters, which is generally used to measure the largest flow rates in practice?

Introduction / Context:
Selecting a flow measurement device depends on range, pressure drop, accuracy, fluid type, and whether the stream is in an open channel or a pipe. Some devices are suited to small flows and sensitive measurements, while others accommodate very large discharges with reasonable headloss.

Given Data / Assumptions:

• We consider typical uses and practical ranges for the devices listed.
• “Largest flow rate” means capability to pass and measure high discharge reliably.
• Fluids are water-like; installation is standard and properly engineered.

Concept / Approach:
Weirs (sharp-crested or broad-crested) are open-channel primary elements commonly used to measure large discharges in rivers, canals, treatment plant outfalls, and reservoir outlets. Their crest widths and head over crest can be scaled to very high flows while maintaining a well-defined head–discharge relation. V-notches are designed for low flows with high sensitivity near the vertex, not for maxima. Rotameters (variable-area meters) are limited by tube size, pressure rating, and float dynamics, favoring small to moderate flows. Orificemeters can handle substantial pipe flows but at the expense of significant permanent pressure loss and mechanical limits; for extremely large discharges, engineered weirs (and flumes) are preferred.

Step-by-Step Solution:

Verification / Alternative check:
Design manuals specify broad-crested weirs and long-throated flumes for high flows; V-notch is reserved for low-flow gauging.

Why Other Options Are Wrong:

• V-notch: High sensitivity at low flows, not high-flow capacity.
• Rotameter: Tube and float constraints limit maximum flows.
• Orificemeter: Handles large pipe flows, but not typically the largest discharges seen in open channels where weirs/flumes dominate.

Common Pitfalls:
Confusing “can pass a lot of fluid” with “measures largest flows with acceptable accuracy and headloss” across applications (pipe vs open channel).

Final Answer:
Weir