According to the Pump Affinity Laws, which relationships are correct?

According to the Pump Affinity Laws, which relationships are correct?

• A. Flow varies directly with speed; Head varies with the square of speed; Power varies with the cube of speed
• B. Flow varies with speed^2; Head varies linearly with speed; Power varies with speed^3
• C. Flow is independent of speed; Head varies with speed^3; Power varies with speed^2
• D. Flow varies inversely with speed; Head varies with square of speed; Power varies with speed

Answer: (A)

Centrifugal pump affinity laws describe how flow, head, and power scale when you change the rotational speed while keeping the impeller size the same. If you double the speed, the flow roughly doubles, the head increases by a factor of four, and the power goes up by about eight times. In general terms for a fixed diameter, flow is proportional to speed, head is proportional to speed squared, and power is proportional to speed cubed. This means that the statement Flow varies directly with speed; Head varies with the square of speed; Power varies with the cube of speed accurately captures the standard relationships used to predict how a pump will behave when its speed is changed. For broader context, if you also change the impeller diameter, the laws become Q ∝ N D^3, H ∝ N^2 D^2, and P ∝ N^3 D^5, but with a fixed diameter the simple N relationships above apply.

Centrifugal pump affinity laws describe how flow, head, and power scale when you change the rotational speed while keeping the impeller size the same. If you double the speed, the flow roughly doubles, the head increases by a factor of four, and the power goes up by about eight times. In general terms for a fixed diameter, flow is proportional to speed, head is proportional to speed squared, and power is proportional to speed cubed. This means that the statement Flow varies directly with speed; Head varies with the square of speed; Power varies with the cube of speed accurately captures the standard relationships used to predict how a pump will behave when its speed is changed. For broader context, if you also change the impeller diameter, the laws become Q ∝ N D^3, H ∝ N^2 D^2, and P ∝ N^3 D^5, but with a fixed diameter the simple N relationships above apply.