ABSA 4B Exam Preparation Document
Section 1: Prime Movers, Engines, and Turbines
1. What is the primary purpose of a governor on a steam turbine?
A. To maintain constant steam pressure entering the turbine
B. To regulate the speed of the turbine under varying load conditions
C. To increase the temperature of the exhaust steam
D. To prevent water hammer in the inlet piping
Option B is correct because the turbine governor adjusts the steam flow valve to maintain a steady
operating speed regardless of changes in electrical or mechanical load. Option A is controlled by
boiler controls, not the turbine governor.
2. In a four-stroke internal combustion engine, during which stroke are both the intake
and exhaust valves fully closed?
A. Intake stroke only
B. Exhaust stroke only
C. Compression and power strokes
D. Intake and power strokes
Option C is correct because both valves must remain tightly sealed during compression to trap the fuel
mixture and during the power stroke to capture expanding gas energy.
3. How does an impulse steam turbine extract mechanical energy from high-pressure
steam?
A. By expanding steam through stationary nozzles to increase velocity and direct it
against moving blades
B. By expanding steam across both stationary and moving blades simultaneously
C. By creating a high backpressure in the exhaust casing
D. By utilizing water injection to increase mass flow rate
Option A is correct because impulse turbines drop pressure solely across stationary nozzles to
produce high-velocity jets that strike the rotor blades. Option B describes reaction turbines.
4. What is the main function of a gas turbine regenerator?
, A. Cool incoming air before it enters the axial compressor
B. Preheat compressed air before entering the combustor using turbine exhaust heat
C. Re-heat gas between turbine expansion stages
D. Remove moisture from the intake air stream
Option B is correct because a regenerator recovers waste heat from hot turbine exhaust gas to
preheat compressed air, reducing fuel consumption in the combustion chamber.
5. What device prevents a steam turbine from overspeeding if the main governor fails?
A. Atmospheric relief valve
B. Throttle pressure regulator
C. Overpressure / Overspeed trip mechanism
D. Sentinel valve
Option C is correct because an overspeed trip mechanism instantly trips the stop valve shut if turbine
RPM exceeds safe operational limits (typically 10-15% above rated speed).
6. Which thermodynamic cycle forms the theoretical basis for steam power plants?
A. Otto cycle
B. Brayton cycle
C. Rankine cycle
D. Diesel cycle
Option C is correct because the Rankine cycle models ideal steam power plant operation involving
evaporation, expansion, condensation, and pumping. Option B models gas turbines.
7. In a multi-stage steam turbine, what is the primary purpose of compounding?
A. To decrease overall thermal efficiency
B. To reduce rotational speed and steam velocity across individual stages
C. To eliminate the need for lubrication systems
D. To increase exhaust steam wetness
Option B is correct because compounding divides pressure or velocity drops across multiple rotor
sets, allowing practical shaft speeds and higher mechanical efficiencies.
8. What component in a reciprocating steam engine converts linear piston motion into
rotational shaft motion?
, A. Crosshead guide
B. Eccentric strap
C. Connecting rod and crankshaft
D. Valve spindle
Option C is correct because the connecting rod attaches the reciprocating piston/crosshead to the
rotating throw of the crankshaft.
9. What safety device warns an operator of excessive pressure buildup in a steam turbine
casing?
A. Sentinel valve
B. Rupture disc
C. Governor valve
D. Extraction check valve
Option A is correct because a small sentinel valve mounted on the turbine casing lifts and emits a
high-pitched whistle when casing pressure rises dangerously.
10. What compression ratio range is typical for a industrial Diesel engine?
A. 6:1 to 10:1
B. 12:1 to 20:1
C. 2:1 to 5:1
D. 25:1 to 40:1
Option B is correct because Diesel engines rely on high compression ratios (12:1 to 20:1) to raise air
temperature high enough to auto-ignite injected fuel.
11. Why is condensation undesirable inside steam turbine expansion stages?
A. It increases steam velocity beyond design limits
B. Water droplets erode turbine blades and reduce efficiency
C. It raises exhaust temperature excessively
D. It causes governor valve binding
Option B is correct because high-velocity moisture droplets strike rotating blades, causing physical
pitting, erosion, and friction losses.
12. What parameter does a gas turbine compressor maintain during normal steady-state
operation?
Section 1: Prime Movers, Engines, and Turbines
1. What is the primary purpose of a governor on a steam turbine?
A. To maintain constant steam pressure entering the turbine
B. To regulate the speed of the turbine under varying load conditions
C. To increase the temperature of the exhaust steam
D. To prevent water hammer in the inlet piping
Option B is correct because the turbine governor adjusts the steam flow valve to maintain a steady
operating speed regardless of changes in electrical or mechanical load. Option A is controlled by
boiler controls, not the turbine governor.
2. In a four-stroke internal combustion engine, during which stroke are both the intake
and exhaust valves fully closed?
A. Intake stroke only
B. Exhaust stroke only
C. Compression and power strokes
D. Intake and power strokes
Option C is correct because both valves must remain tightly sealed during compression to trap the fuel
mixture and during the power stroke to capture expanding gas energy.
3. How does an impulse steam turbine extract mechanical energy from high-pressure
steam?
A. By expanding steam through stationary nozzles to increase velocity and direct it
against moving blades
B. By expanding steam across both stationary and moving blades simultaneously
C. By creating a high backpressure in the exhaust casing
D. By utilizing water injection to increase mass flow rate
Option A is correct because impulse turbines drop pressure solely across stationary nozzles to
produce high-velocity jets that strike the rotor blades. Option B describes reaction turbines.
4. What is the main function of a gas turbine regenerator?
, A. Cool incoming air before it enters the axial compressor
B. Preheat compressed air before entering the combustor using turbine exhaust heat
C. Re-heat gas between turbine expansion stages
D. Remove moisture from the intake air stream
Option B is correct because a regenerator recovers waste heat from hot turbine exhaust gas to
preheat compressed air, reducing fuel consumption in the combustion chamber.
5. What device prevents a steam turbine from overspeeding if the main governor fails?
A. Atmospheric relief valve
B. Throttle pressure regulator
C. Overpressure / Overspeed trip mechanism
D. Sentinel valve
Option C is correct because an overspeed trip mechanism instantly trips the stop valve shut if turbine
RPM exceeds safe operational limits (typically 10-15% above rated speed).
6. Which thermodynamic cycle forms the theoretical basis for steam power plants?
A. Otto cycle
B. Brayton cycle
C. Rankine cycle
D. Diesel cycle
Option C is correct because the Rankine cycle models ideal steam power plant operation involving
evaporation, expansion, condensation, and pumping. Option B models gas turbines.
7. In a multi-stage steam turbine, what is the primary purpose of compounding?
A. To decrease overall thermal efficiency
B. To reduce rotational speed and steam velocity across individual stages
C. To eliminate the need for lubrication systems
D. To increase exhaust steam wetness
Option B is correct because compounding divides pressure or velocity drops across multiple rotor
sets, allowing practical shaft speeds and higher mechanical efficiencies.
8. What component in a reciprocating steam engine converts linear piston motion into
rotational shaft motion?
, A. Crosshead guide
B. Eccentric strap
C. Connecting rod and crankshaft
D. Valve spindle
Option C is correct because the connecting rod attaches the reciprocating piston/crosshead to the
rotating throw of the crankshaft.
9. What safety device warns an operator of excessive pressure buildup in a steam turbine
casing?
A. Sentinel valve
B. Rupture disc
C. Governor valve
D. Extraction check valve
Option A is correct because a small sentinel valve mounted on the turbine casing lifts and emits a
high-pitched whistle when casing pressure rises dangerously.
10. What compression ratio range is typical for a industrial Diesel engine?
A. 6:1 to 10:1
B. 12:1 to 20:1
C. 2:1 to 5:1
D. 25:1 to 40:1
Option B is correct because Diesel engines rely on high compression ratios (12:1 to 20:1) to raise air
temperature high enough to auto-ignite injected fuel.
11. Why is condensation undesirable inside steam turbine expansion stages?
A. It increases steam velocity beyond design limits
B. Water droplets erode turbine blades and reduce efficiency
C. It raises exhaust temperature excessively
D. It causes governor valve binding
Option B is correct because high-velocity moisture droplets strike rotating blades, causing physical
pitting, erosion, and friction losses.
12. What parameter does a gas turbine compressor maintain during normal steady-state
operation?
