What is the function of a non-return valve?
- ABlocks the flow of fluid in all directions in a pipe flow system
- BAllows flow of liquid in a direction opposite to the pumping direction of liquid
- CAllow the flow of liquid in both upward and downward direction in a pipe flow system
- DAllow the flow of liquid in one direction and prevents it from flowing back in opposite direction in a pipe flow systemCorrect
Solution
Concept
A non-return valve lets water flow in one direction only and stops back flow.
Step-by-step solution
1. A non-return valve is also called a check valve or reflux valve. 2. It opens when water flows in the forward (pumping) direction. 3. When the flow tries to reverse, the valve flap closes automatically. 4. So it allows flow in one direction and prevents back flow. Answer is D.
Explanation
A non-return valve allows water to move only in the forward direction. If the pump stops, water tries to flow back, and the valve closes automatically. This protects the pump and stops the pipe from emptying.
Why the other options are wrong
A: A valve that blocks flow in all directions is just a closed sluice valve, not a non-return valve. B: It does the opposite. It stops flow against the pumping direction. C: Allowing flow both ways is the job of a normal open valve, not a non-return valve.
Shortcut
Non-return means no return: one-way flow only.
Common mistake
Confusing the non-return (reflux) valve with the sluice valve or the air relief valve.
Correct answer: D) Allow the flow of liquid in one direction and prevents it from flowing back in opposite direction in a pipe flow system