Centrifugal Pumps and their Characteristics

Centrifugal pumps are widely used in various industries to move fluids by converting mechanical energy into hydraulic energy. These pumps have several characteristics that determine their performance. Let's examine the given options and explain why option A is the correct answer.

Option A: The discharge varies directly as the speed

The discharge of a centrifugal pump refers to the volume flow rate of fluid being pumped. It is measured in units such as liters per second or gallons per minute. The given option states that the discharge varies directly as the speed. This means that as the speed of the pump increases, the discharge also increases in direct proportion.

Explanation:
- When a centrifugal pump operates at a higher speed, the impeller inside the pump rotates at a faster rate.
- The impeller blades create a centrifugal force that propels the fluid towards the outer edges of the impeller.
- As the fluid is pushed towards the outer edges, it is forced into the pump casing and eventually discharged through the outlet.
- The faster the impeller rotates, the more fluid can be pushed towards the outlet, resulting in a higher discharge.

Other Options:

Let's briefly discuss why the other options are incorrect:

Option B: The head varies inversely as the speed
- The head of a centrifugal pump refers to the energy transferred to the fluid per unit weight.
- The head is responsible for the pressure and height the pump can lift the fluid.
- In a centrifugal pump, the head does not vary inversely as the speed but rather directly with the speed.
- Increasing the speed of the pump will result in an increase in the head.

Option C: The power varies as the square of the speed
- The power of a centrifugal pump refers to the mechanical energy input required to drive the pump.
- The power consumed by a centrifugal pump is directly proportional to the cube of the speed, not the square.
- As the speed of the pump increases, the power required to drive the pump increases significantly.

Option D: The discharge varies as the square of the speed
- The discharge of a centrifugal pump does not vary as the square of the speed but rather varies directly with the speed.
- Increasing the speed of the pump will result in a proportional increase in the discharge.

Conclusion:

From the given options, it is clear that option A is the correct answer. The discharge of a centrifugal pump varies directly as the speed. However, it is important to note that the performance characteristics of a centrifugal pump may vary depending on the design, impeller size, and other factors.