Step 1: Define centrifugal pump characteristic curves.
These are graphical representations of a pump's performance, illustrating the interplay between head, discharge (flow rate), brake horsepower (BHP), and efficiency at a fixed rotational speed.
Step 2: Identify the standard characteristic curves.
The independent variable, typically plotted on the x-axis, is the discharge (Q). The key performance parameters are then plotted against discharge:
- D. Discharge versus Head (H-Q curve): This is the principal performance curve, demonstrating that the head generated by a pump diminishes as the flow rate rises. This relationship is fundamental.
- C. BHP versus Discharge (P-Q curve): This illustrates the power demand of the pump. Typically, BHP increases from a minimum at zero discharge to a maximum as discharge increases.
- A. Discharge versus Efficiency (\(\eta\)-Q curve): This shows that efficiency is zero at zero discharge, peaks at a single value (the Best Efficiency Point or BEP), and then declines as discharge further increases.
Relationships such as "Head versus BHP" (B) and "Efficiency versus Head" (E) are not standard primary characteristic curves; they can be derived from the main three but are not the direct relationships plotted.
Step 3: Conclude the correct combination.
The standard relationships plotted for a centrifugal pump are A (Discharge vs Efficiency), C (BHP vs Discharge), and D (Discharge vs Head).