Hydraulic Machines Flashcards

What is cavitation in a centrifugal pump?

Answer: Formation and collapse of vapor bubbles due to local pressure drop below vapor pressure

Cavitation occurs when local pressure falls below the liquid's vapor pressure, causing vapor bubbles that implode violently and damage pump components.

The Net Positive Suction Head Available (NPSHA) must be:

Answer: Greater than NPSHR to prevent cavitation

NPSHA must exceed NPSHR (required) by a sufficient margin to ensure local pressures never drop to vapor pressure and cavitation does not occur.

In a Pelton wheel turbine, the jet of water strikes:

Answer: Cup-shaped buckets tangentially

A Pelton wheel is an impulse turbine where high-velocity jets strike cup-shaped (double-hemispherical) buckets tangentially, converting kinetic energy to mechanical work.

The specific speed of a turbine is used to:

Answer: Classify turbine type and predict performance similarity

Specific speed is a dimensionless (or dimensional) similarity parameter that classifies turbine types and allows performance prediction across geometrically similar machines.

Which hydraulic turbine is best suited for high head and low flow rate conditions?

Answer: Pelton wheel

The Pelton wheel operates efficiently under very high heads (hundreds to thousands of meters) with relatively low volumetric flow rates.

The draft tube in a reaction turbine primarily serves to:

Answer: Recover kinetic energy at runner exit and allow turbine placement above tailrace

The draft tube decelerates the flow leaving the runner, converting kinetic energy back to pressure energy, and enables the turbine to be installed above the tailwater level.

In a double-acting reciprocating pump, fluid is discharged during:

Answer: Both the forward and return strokes

A double-acting reciprocating pump has cylinders on both sides of the piston, so discharge occurs during both strokes, giving more uniform flow than a single-acting design.