Understanding Multi-Stage Centrifugal Pumps

A multi-stage centrifugal pump is a pump that has two or more impellers connected in series on the same shaft within a single casing. Unlike a single-stage pump which has only one impeller, the multi-stage design utilizes multiple impellers to increase the overall pressure or head developed by the pump.

Functionality for High Heads

The primary purpose of connecting impellers in series in a multi-stage centrifugal pump is to increase the total head. When fluid passes through the first impeller, its pressure (and thus head) is increased. This higher pressure fluid then enters the second impeller, where its pressure is increased further. This process continues through all subsequent impellers.

In a series arrangement, the heads produced by each individual impeller stage add up to produce a much higher total head at the pump's outlet compared to what a single impeller could achieve at the same flow rate. The flow rate through all stages remains approximately the same.

• Connecting impellers in series increases the head.
• Connecting impellers in parallel increases the discharge (flow rate).

Analyzing the Options

Let's look at the given options in the context of multi-stage centrifugal pumps:

• Give high discharge: High discharge is typically achieved by connecting pumps or impellers in parallel, not series. Multi-stage pumps use series connection to boost head, not discharge.
• Produce high heads: As explained, the series arrangement of impellers in a multi-stage pump is specifically designed to accumulate the head developed by each stage, resulting in a significantly higher total head. This is the main application for these pumps.
• Pump viscous fluids: While centrifugal pumps can handle some viscous fluids, multi-stage pumps are not primarily designed for this characteristic. Pumping highly viscous fluids often requires different pump types (like positive displacement pumps) or specially designed centrifugal pumps with specific impeller and casing geometry. The multi-stage design doesn't inherently improve viscous fluid handling over a single-stage pump of similar design; its advantage lies in head generation.
• All of these: Since multi-stage pumps are not primarily used for high discharge or exclusively for pumping viscous fluids compared to other types, this option is incorrect.

Therefore, the most accurate description of the primary use of multi-stage centrifugal pumps is to produce high heads for applications requiring fluid to be pumped against high resistance or to significant elevations.