Pumps and Compressors Flashcards

What is a screw compressor's oil separator and why is it important?

Answer: It removes the injected oil from the compressed air discharge, ensuring clean air delivery and returning oil to the compressor for reuse

In oil-injected screw compressors, oil is injected into the compression chamber for sealing, cooling, and lubrication. The oil separator in the discharge removes this oil from the compressed air stream and returns it to the compressor, delivering clean air downstream.

What is the function of a pump's bearing frame (bearing housing)?

Answer: To support the shaft bearings, maintain proper bearing alignment, contain lubricant, and provide cooling

The bearing frame supports and houses the radial and thrust bearings that carry the shaft loads, maintains precise bearing alignment, contains the lubricant (oil bath or grease), and often includes cooling provisions to manage bearing temperature.

What is the difference between an axial flow pump and a radial flow centrifugal pump?

Answer: An axial flow pump moves fluid parallel to the shaft axis using a propeller-like impeller, while a radial flow pump moves fluid perpendicular to the shaft using a traditional impeller

An axial flow pump uses a propeller-type impeller that pushes fluid along the shaft axis — ideal for very high flows at low head. A radial flow pump uses a traditional impeller that throws fluid outward radially — better suited for higher head at moderate flows.

What is the purpose of a compressor's capacity control system?

Answer: To match the compressor's output to system demand, preventing over-pressurization and reducing energy consumption during partial load

Capacity control systems match compressor output to varying system demand. Methods include inlet throttling, variable speed drive, slide valve (on screw compressors), cylinder unloading, and start/stop control, all aimed at saving energy during partial load conditions.

Why should a centrifugal pump not be operated for extended periods with the suction strainer clogged?

Answer: A clogged strainer restricts suction flow, reducing available NPSH and causing cavitation damage to the impeller and reduced pump performance

A clogged suction strainer creates a high pressure drop on the suction side, reducing the available NPSH below the pump's required NPSH. This causes cavitation — vaporization and violent bubble collapse at the impeller — resulting in erosion damage and reduced performance.

What is a double mechanical seal and when is it used?

Answer: Two seal assemblies with a barrier fluid between them, used when pumping hazardous, toxic, or volatile fluids that must not leak to atmosphere

A double mechanical seal has two seal sets with a pressurized or unpressurized barrier fluid between them. If the inner seal leaks, the barrier fluid contains the process fluid. This is required for toxic, flammable, or environmentally hazardous fluids.