Mechanical
A hydraulic turbine is a machine that converts hydraulic energy into:
- Mechanical energy
- Electrical energy directly
- Chemical energy
- Thermal energy
Explanation:
- A hydraulic turbine extracts energy from flowing or falling water and converts it into mechanical shaft power.
- The mechanical power can then be used to drive an electrical generator.
Hydraulic turbines are broadly classified according to the energy available at the runner inlet as:
- Impulse and reaction turbines
- Reciprocating and rotary turbines
- Positive and negative turbines
- Open and closed turbines only
Explanation:
- In an impulse turbine, the available hydraulic energy is converted largely into kinetic energy before water strikes the runner.
- In a reaction turbine, water pressure changes while flowing through the runner in addition to changes in velocity.
Which turbine operates mainly by converting the available head into a high-velocity jet before water strikes the runner?
- Impulse turbine
- Reaction turbine
- Centrifugal pump
- Reciprocating pump
Explanation:
- In an impulse turbine, the nozzle converts pressure/head energy into kinetic energy.
- The high-velocity jet then strikes the runner buckets and transfers momentum to the runner.
- Pelton turbine is the standard example.
Which of the following is an impulse hydraulic turbine?
- Pelton turbine
- Francis turbine
- Kaplan turbine
- Propeller turbine
Explanation:
- The Pelton turbine is an impulse turbine.
- It is generally used for high-head and relatively low-flow applications.
- Francis and Kaplan turbines are reaction turbines.
Which of the following is a reaction turbine?
- Francis turbine
- Pelton turbine
- Turgo impulse turbine
- Cross-flow impulse turbine
Explanation:
- Francis turbine is a reaction turbine.
- It is commonly used for medium-head applications, although its practical operating range is broad.
- Water undergoes pressure and velocity changes while passing through the runner.
Which hydraulic turbine is commonly used for low-head and high-flow applications?
- Kaplan turbine
- Pelton turbine
- Impulse turbine only
- Reciprocating turbine
Explanation:
- Kaplan turbine is an axial-flow reaction turbine.
- It is well suited to low-head, high-flow conditions.
- Its runner blades are adjustable in many designs, allowing efficient operation over varying loads.
Which hydraulic turbine is generally suitable for high-head applications?
- Pelton turbine
- Kaplan turbine
- Propeller turbine
- Francis turbine only
Explanation:
- Pelton turbines are particularly suitable for high heads and relatively low flow rates.
- Water is converted into a high-velocity jet by a nozzle before entering the runner.
Francis turbine is generally classified as a:
- Mixed-flow reaction turbine
- Pure impulse turbine
- Axial-flow impulse turbine
- Positive-displacement turbine
Explanation:
- Francis turbine is a reaction turbine with mixed flow through the runner.
- Water generally enters the runner radially or approximately radially and leaves approximately axially.
Kaplan turbine is generally classified as a:
- Axial-flow reaction turbine
- Radial-flow impulse turbine
- Mixed-flow impulse turbine
- Positive-displacement turbine
Explanation:
- Kaplan turbine is an axial-flow reaction turbine.
- Water flows substantially parallel to the shaft through the runner.
- It is suitable for low-head, high-flow installations.
In an impulse turbine, the pressure across the runner is ideally:
- Approximately constant
- Continuously increased
- Continuously decreased due to reaction effect
- Zero everywhere
Explanation:
- In an ideal impulse turbine, pressure energy is converted into kinetic energy before the water reaches the runner.
- The runner primarily extracts kinetic energy from the jet.
- Therefore, there is ideally no significant pressure drop across the runner itself.
In a reaction turbine, the pressure of water across the runner:
- Changes as water passes through the runner
- Remains exactly constant
- Becomes atmospheric at every point
- Always increases
Explanation:
- Pressure changes through the runner are an important characteristic of reaction turbines.
- Both pressure and velocity changes contribute to energy transfer.
Which component converts pressure energy of water into kinetic energy in an impulse turbine?
- Nozzle
- Draft tube
- Runner casing
- Tailrace
Explanation:
- The nozzle converts the available pressure/head energy into kinetic energy and produces a high-velocity jet.
- The jet then transfers momentum to the runner buckets.
The main function of buckets in a Pelton turbine is to:
- Receive the high-velocity jet and change its momentum
- Increase water pressure
- Act as a draft tube
- Store water permanently
Explanation:
- Pelton buckets are shaped to deflect the incoming water jet substantially.
- The change in momentum produces a force on the buckets and consequently torque on the runner.
The characteristic bucket shape of a Pelton turbine is approximately:
- Double-cupped with a central splitter
- Flat rectangular plate
- Helical screw
- Cylindrical piston
Explanation:
- Pelton buckets are approximately double-cupped and have a splitter at the center.
- The splitter divides the incoming jet into two streams flowing over the bucket surfaces.
What is the main function of a draft tube in a reaction turbine?
- To recover kinetic energy at the runner exit and permit the turbine to be located above the tailwater
- To convert water into steam
- To increase runner inlet pressure by combustion
- To supply fuel to the turbine
Explanation:
- A draft tube is fitted at the outlet of a reaction turbine.
- It gradually enlarges, reducing flow velocity and recovering part of the kinetic energy as pressure energy.
- It also allows the turbine runner to be located above the tailwater level.
Cavitation in a hydraulic turbine is mainly caused when local pressure falls:
- Below the vapour pressure of water
- Above atmospheric pressure
- Above the critical pressure of steel
- Exactly equal to reservoir pressure
Explanation:
- When local pressure falls below the vapour pressure, vapour bubbles can form.
- When these bubbles move to higher-pressure regions, they collapse and can cause noise, vibration, erosion and performance loss.
Which parameter is commonly used to classify hydraulic turbines for selection according to head, speed and discharge conditions?
- Specific speed
- Specific gravity only
- Absolute viscosity only
- Density only
Explanation:
- Specific speed is a useful parameter for comparing turbine types and selecting a suitable turbine for given head and power conditions.
- Pelton, Francis and Kaplan turbines occupy different practical specific-speed ranges.
A hydraulic turbine primarily operates by extracting energy from:
- Water flow
- Fuel combustion
- Compressed air only
- Steam condensation only
Explanation:
- Hydraulic turbines use the hydraulic energy of water.
- The available energy may be associated with elevation head, pressure head and velocity head.
Which turbine generally has adjustable runner blades?
- Kaplan turbine
- Pelton turbine
- Simple Francis turbine only
- Cross-flow impulse turbine
Explanation:
- Kaplan turbines commonly use adjustable-pitch runner blades.
- Many Kaplan turbines also have adjustable guide vanes.
- This arrangement provides good efficiency over a range of flow rates.
A centrifugal pump converts mechanical energy supplied to its shaft primarily into:
- Hydraulic energy of the fluid
- Electrical energy directly
- Chemical energy
- Nuclear energy
Explanation:
- A centrifugal pump receives mechanical shaft power from a motor or engine.
- The impeller transfers energy to the fluid, increasing its velocity and pressure/head.
A centrifugal pump is classified as a:
- Rotodynamic pump
- Positive-displacement pump
- Reciprocating pump
- Steam turbine
Explanation:
- Centrifugal pumps are rotodynamic pumps.
- They continuously transfer energy to the fluid through a rotating impeller.
- Reciprocating and rotary pumps such as gear pumps are positive-displacement pumps.
The main rotating component of a centrifugal pump that imparts energy to the fluid is the:
- Impeller
- Volute casing only
- Foot valve
- Delivery pipe
Explanation:
- The impeller rotates and transfers mechanical energy to the liquid.
- The liquid gains velocity and pressure/head as it passes through the pump.
According to the direction of flow through the impeller, centrifugal pumps may be classified as:
- Radial-flow, mixed-flow and axial-flow pumps
- Hot and cold pumps only
- Gas and liquid pumps only
- Metal and non-metal pumps only
Explanation:
- Radial-flow pumps discharge fluid approximately perpendicular to the shaft.
- Mixed-flow pumps have both radial and axial components.
- Axial-flow pumps discharge approximately parallel to the shaft.
In a radial-flow centrifugal pump, the fluid generally leaves the impeller:
- In a direction approximately perpendicular to the shaft
- Exactly parallel to the shaft
- Without changing direction
- Only downward
Explanation:
- In radial-flow pumps, the major component of discharge velocity is radial.
- These pumps are commonly used where relatively higher heads are required.
A centrifugal pump having several impellers arranged in series is called a:
- Multistage pump
- Single-stage pump
- Reciprocating pump
- Jet pump
Explanation:
- In a multistage centrifugal pump, multiple impellers are arranged in series.
- The head developed by the stages adds approximately, subject to losses and design conditions.
- Such pumps are used where high heads are required.
When several impellers are arranged in parallel, the primary purpose is to increase:
- Discharge capacity
- Fluid viscosity
- Pipe roughness
- Specific gravity of the liquid
Explanation:
- Parallel pump arrangements increase the flow capacity while operating approximately at the same head.
- Series arrangement is generally used to obtain higher head.
What is the basic working principle of a centrifugal pump?
- The rotating impeller imparts kinetic energy to the liquid, which is partly converted into pressure energy
- The liquid is compressed by a piston
- The liquid is heated until it becomes steam
- The liquid is moved only by gravity
Explanation:
- The impeller increases the velocity and energy of the liquid.
- The casing or diffuser converts a portion of the velocity head into pressure head.
- This enables the pump to deliver liquid at the required head.
Why is priming required in a conventional centrifugal pump before starting?
- To remove air from the pump casing and suction line and fill them with liquid
- To increase the motor speed
- To lubricate the delivery pipe
- To reduce atmospheric pressure
Explanation:
- A conventional centrifugal pump generally cannot develop the required suction action if air occupies the casing and suction line.
- Priming fills the pump and suction line with the liquid to be pumped.
- Self-priming designs use special arrangements to reduce the need for manual priming.
Which component is commonly provided at the lower end of the suction pipe to prevent reverse flow when the pump stops?
- Foot valve
- Delivery valve
- Pressure gauge
- Air vessel
Explanation:
- A foot valve is a non-return valve fitted near the lower end of the suction pipe in many conventional installations.
- It helps retain liquid in the suction pipe and pump casing after stopping.
The function of the volute casing in a centrifugal pump is mainly to:
- Collect the liquid from the impeller and convert part of velocity head into pressure head
- Supply fuel to the motor
- Prevent all rotation of the impeller
- Heat the liquid
Explanation:
- The volute casing has an increasing cross-sectional area around the impeller.
- As flow velocity decreases, part of the kinetic energy is converted into pressure energy.
- A diffuser casing performs a similar energy-conversion function using diffuser passages.
Which quantity represents the energy supplied by the pump to the liquid per unit weight?
- Pump head
- Specific gravity
- Viscosity
- Displacement
Explanation:
- Pump head is commonly expressed in metres of liquid and represents energy per unit weight.
- It is related to the increase in total head of the liquid across the pump.
What happens to the theoretical head developed by a centrifugal pump when the impeller speed increases, under similar conditions?
- It generally increases approximately with the square of speed
- It always decreases with speed
- It remains exactly constant
- It becomes zero
Explanation:
- According to the affinity laws for geometrically similar operation with the same impeller diameter, head varies approximately as N2.
- Discharge varies approximately as N and power approximately as N3, subject to the usual similarity assumptions.
According to the affinity laws, the discharge of a centrifugal pump varies approximately with:
- Speed N
- N2
- N3
- 1/N2
Explanation:
- For the same impeller diameter and similar operating conditions:
- Q ∝ N
- H ∝ N2
- P ∝ N3
According to the affinity laws, the power required by a centrifugal pump varies approximately with:
- N3
- N
- N2
- 1/N
Explanation:
- For similar operation with unchanged impeller diameter, pump power varies approximately as the cube of rotational speed.
- Therefore, even a moderate increase in speed can cause a significant increase in power requirement.
Which curve represents the relationship between pump head and discharge for a particular pump at constant speed?
- Head-discharge characteristic curve
- Temperature-entropy curve
- Stress-strain curve
- Load-extension curve
Explanation:
- The pump characteristic curve generally plots head developed against discharge at a specified speed.
- Other important pump performance curves include efficiency versus discharge and power versus discharge.
The operating point of a centrifugal pump in a piping system is determined by the intersection of:
- Pump characteristic curve and system resistance curve
- Temperature and entropy curves
- Stress and strain curves
- Torque and angular displacement curves
Explanation:
- The pump supplies head according to its characteristic curve.
- The piping system requires a head that depends on static head and flow-dependent losses.
- The intersection of the two curves determines the operating discharge and head.
What is pump efficiency?
- Ratio of useful hydraulic power delivered to the power supplied to the pump
- Ratio of input power to hydraulic power
- Ratio of discharge to pressure
- Ratio of speed to head
Explanation:
- Pump overall efficiency can be expressed as:
- η = Hydraulic power / Shaft power
- Hydraulic power is commonly represented by ρgQH.
The hydraulic power delivered by a pump to a liquid is given by:
- ρgQH
- ρQ/H
- gH/Q
- Q/(ρgH)
Explanation:
- Hydraulic power = ρgQH.
- Here, ρ is liquid density, g is gravitational acceleration, Q is discharge and H is pump head.
- When ρ is in kg/m3, Q in m3/s and H in m, the result is in watts.
What is the manometric efficiency of a centrifugal pump?
- Ratio of manometric head to theoretical head imparted by the impeller
- Ratio of shaft power to discharge
- Ratio of suction pressure to atmospheric pressure
- Ratio of actual discharge to theoretical discharge only
Explanation:
- Manometric efficiency compares the actual head developed by the pump with the theoretical head imparted by the impeller.
- It accounts for hydraulic effects and losses between the impeller and pump delivery.
What is mechanical efficiency of a centrifugal pump?
- Ratio of power transferred to the fluid by the impeller to shaft power supplied
- Ratio of discharge to head
- Ratio of suction head to delivery head
- Ratio of hydraulic power to discharge only
Explanation:
- Mechanical efficiency accounts mainly for mechanical losses such as bearing, seal and disc-friction losses.
- It compares the power actually transferred by the impeller to the fluid with the shaft power supplied to the pump.
What is volumetric efficiency of a centrifugal pump?
- Ratio of actual discharge to theoretical discharge
- Ratio of shaft power to hydraulic power
- Ratio of head to speed
- Ratio of pressure to density
Explanation:
- Volumetric efficiency accounts for leakage and other effects that cause the actual discharge to differ from the theoretical discharge.
- It is generally expressed as actual discharge divided by theoretical discharge.
Cavitation in a centrifugal pump occurs when the local absolute pressure falls:
- Below the vapour pressure of the liquid
- Above atmospheric pressure
- Above delivery pressure
- Exactly equal to atmospheric pressure
Explanation:
- If local pressure falls below the liquid vapour pressure, vapour bubbles form.
- The bubbles can collapse when they reach higher-pressure regions, causing noise, vibration, erosion and reduction in pump performance.
Which parameter is particularly important for assessing the tendency of a centrifugal pump installation to cavitate?
- Net Positive Suction Head (NPSH)
- Brake power only
- Specific gravity only
- Discharge pipe diameter only
Explanation:
- NPSH describes the suction-side pressure head available above the liquid vapour pressure.
- For satisfactory operation, NPSH available should be greater than the NPSH required by the pump, with an appropriate margin.
Which condition generally increases the possibility of cavitation in a centrifugal pump?
- Low suction pressure
- Higher suction pressure
- Lower liquid temperature in all cases
- Reduced pump speed in every situation
Explanation:
- Low suction pressure reduces the margin between local absolute pressure and vapour pressure.
- High liquid temperature also tends to increase vapour pressure and can increase cavitation risk.
- Proper suction design and adequate NPSH are essential.
Which arrangement is generally used when a high head is required from centrifugal pumps?
- Pumps in series
- Pumps in parallel only
- Open suction pipe only
- Single impeller removed
Explanation:
- When pumps are connected in series, their heads approximately add at a given flow, subject to system and pump characteristics.
- Parallel pumps are generally used to increase the available discharge.
When centrifugal pumps are connected in parallel, the main objective is to obtain:
- Higher discharge capacity
- Higher fluid density
- Lower liquid temperature
- Zero suction head
Explanation:
- Parallel operation combines the flow contributions of the pumps.
- It is useful when the system requires a larger flow rate than one pump can provide.
Which component controls the flow in many centrifugal pump delivery systems?
- Delivery valve
- Foot valve
- Impeller eye
- Bearings
Explanation:
- The delivery valve can be used to regulate the discharge from the pump.
- During normal operation, the system operating point depends on the pump and system characteristics.
The power transmitted to the fluid by a centrifugal pump is directly proportional to:
- ρgQH
- ρg/(QH)
- Q/(ρgH)
- H/(ρgQ)
Explanation:
- Hydraulic power is Ph = ρgQH.
- Therefore, for a given liquid, increasing discharge or pump head increases the hydraulic power delivered to the fluid.
Which statement correctly compares impulse and reaction hydraulic turbines?
- Impulse turbines use a jet with negligible pressure change through the runner, while reaction turbines have pressure change through the runner
- Both always have identical pressure behavior
- Reaction turbines never use guide vanes
- Impulse turbines always require a draft tube
Explanation:
- In an impulse turbine, most of the pressure/head energy is converted into jet velocity before the runner.
- In a reaction turbine, the runner experiences a pressure change as well as a velocity change.
- Draft tubes are associated with reaction turbines, not conventional Pelton impulse turbines.
Which turbine-pump pair is correctly matched?
- Pelton — impulse turbine; Kaplan — axial-flow reaction turbine
- Pelton — reaction turbine; Kaplan — impulse turbine
- Francis — impulse turbine; Pelton — axial reaction turbine
- Kaplan — reciprocating turbine; Pelton — centrifugal pump
Explanation:
- Pelton is an impulse turbine.
- Francis is a mixed-flow reaction turbine.
- Kaplan is an axial-flow reaction turbine.
- These classifications are important for turbine selection based on head and flow conditions.