Question

Which of the following intruments are used to measure cumulative flow of water?
A. Propeller meter
B. Elbow meter
C. Deathridge meter
D. Water meter
Choose the correct answer from the options given below

• A. A and B only
• B. C and D only
• C. B, C and D only
• D. A, C and D only

Hint:

Remember that differential pressure devices like elbow meters, venturimeters, and orifice plates measure instantaneous flow rates. Rotational and volumetric devices like propeller, Deathridge, and water meters measure cumulative volume.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Water flow measurement devices are classified based on their operating principles:
- Rate meters: Measure the instantaneous rate of flow (e.g., liters per second, cubic meters per hour).
- Quantity (or integrating) meters: Measure the total volume of water passing through the section over a period (cumulative flow).

Step 2: Detailed Explanation:
Let us examine each instrument listed:
- A. Propeller meter: This is an integrating flow meter that uses a rotating propeller.
The speed of rotation is proportional to velocity, and an internal gear mechanism integrates this over time to display the cumulative volume of water. This is used for cumulative flow.
- B. Elbow meter: This is a differential-pressure type meter that utilizes the centripetal force developed in a pipe elbow.
It measures the difference in pressure between the inner and outer bends to calculate the instantaneous flow rate. It is not an integrating meter and does not directly measure cumulative flow.
- C. Deathridge meter: This is a low-head, open-channel integrating water meter used in irrigation channels.
It uses a vane wheel that rotates as water passes, integrating the rotations to record cumulative flow volume.
- D. Water meter: A generic class of displacement or velocity-type meters installed in closed pipes to directly record the cumulative volume of water consumed.
Therefore, instruments A, C, and D are used to measure cumulative flow.

Step 3: Final Answer:
The instruments used to measure cumulative flow of water are A, C and D only.