Pumps and Compressors Flashcards

What is the difference between a single-stage and a multi-stage centrifugal pump?

Answer: A single-stage pump has one impeller while a multi-stage pump has multiple impellers in series, each adding head (pressure) to the fluid

A single-stage pump has one impeller and produces head in a single step. A multi-stage pump has multiple impellers arranged in series, with the output of each stage feeding the next, progressively adding head to achieve much higher discharge pressures.

What is the purpose of the volute casing in a centrifugal pump?

Answer: To gradually increase the cross-sectional area of the flow path, converting the velocity energy from the impeller into pressure energy

The volute is a spiral-shaped casing that surrounds the impeller. Its gradually increasing cross-sectional area slows the high-velocity fluid leaving the impeller, converting kinetic (velocity) energy into pressure energy according to Bernoulli's principle.

What is a reciprocating compressor and where is it commonly used?

Answer: A compressor using pistons driven by a crankshaft to compress gas in cylinders, commonly used for high-pressure applications

A reciprocating compressor uses pistons driven by a crankshaft to compress gas in cylinders, similar to an internal combustion engine. It is commonly used in high-pressure applications including industrial air supply, natural gas processing, and refrigeration.

What is the function of an intercooler between stages of a multi-stage compressor?

Answer: To cool the compressed gas between stages, reducing its volume, lowering discharge temperature, and improving compression efficiency

Compression heats the gas significantly. An intercooler removes this heat between stages, reducing the gas volume entering the next stage, lowering the overall discharge temperature, reducing power consumption, and bringing the compression process closer to isothermal (ideal) efficiency.

What is the purpose of a compressor unloader?

Answer: To reduce or eliminate the compressor's pumping capacity during low-demand periods without stopping the motor

A compressor unloader allows the compressor motor to continue running while reducing or eliminating the compression workload during low-demand periods. Methods include holding suction valves open, closing suction ports, or bypassing discharge to suction.

Why is it important to check the direction of rotation before starting a centrifugal pump?

Answer: Reverse rotation produces little or no flow and pressure, and can damage the pump, loosen the impeller, or cause the mechanical seal to fail

A centrifugal pump impeller is designed to work in one direction only. Reverse rotation produces drastically reduced performance, can unscrew threaded impellers from the shaft, damage mechanical seals, and cause the pump to overheat from churning fluid without producing useful flow.