slurry pump casing unit

Questions on Centrifugal Pumps

Answers on Centrifugal Pumps

What is a centrifugal pump? A centrifugal pump is a hydraulic machine that uses a rotating impeller to impart velocity to a fluid and convert this velocity into pressure energy.

Difference between centrifugal and positive displacement pumps:

Centrifugal Pumps: Flow varies with system resistance, suitable for large volume and low viscosity fluids.

Positive Displacement Pumps: Deliver fixed flow irrespective of pressure, best for high-viscosity or high-pressure applications.

What is NPSH? NPSH (Net Positive Suction Head) is the minimum pressure required at the pump suction to avoid cavitation. There are two types:

NPSH Available (NPSHa)

NPSH Required (NPSHr)

What is cavitation? Cavitation is the formation and sudden collapse of vapor bubbles inside the pump due to low pressure. This causes vibration, noise, damage to the impeller, and efficiency loss.

Main parts of a centrifugal pump:

Impeller: The rotating element that moves the fluid.

Casing: Directs fluid flow and converts velocity into pressure.

Shaft & Bearings: Support the impeller rotation.

Mechanical Seal/Gland Packing: Prevents leakages.

Suction & Delivery Nozzles: Entry and exit points for fluid.

Single-stage vs multi-stage pump:

Single-stage Pump: Contains one impeller; simpler design, suitable for low to medium head applications.

Multi-stage Pump: Contains two or more impellers in series; used for high head applications like boiler feed pumps.

What are pump characteristic curves? These are performance graphs showing relationships such as:

Head vs Flow rate

Efficiency vs Flow rate

Power vs Flow rate

NPSH Required vs Flow rate

What is priming? Priming is the process of filling the pump and suction pipe with liquid before starting it to remove air and ensure smooth operation.

Factors affecting efficiency:

Impeller design and wear

Pump speed

Occurrence of cavitation

Mechanical losses (friction, leakage)

Proper alignment and maintenance

Common causes of failure:

Cavitation damage

Seal or gasket failure

Bearing wear due to poor lubrication

Impeller erosion or corrosion

Operating away from the Best Efficiency Point (BEP)