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Question 1
ప్రశ్న 1
What is the conventional physical interpretation of the specific speed of a pump?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
Pump specific speed is a similarity parameter used to characterize a homologous family of pumps. Conventionally, it may be interpreted as the rotational speed of a geometrically similar pump that would deliver unit discharge against unit head. It therefore provides information about the general impeller form appropriate to a duty point. It is not the actual maximum or minimum operating speed of the installed pump. Therefore Option A is correct.
వివరణ:
Question 2
ప్రశ్న 2
Using the convention Ns = N sqrt(Q)/H^(3/4), which statement correctly distinguishes pump specific speed from conventional turbine specific speed?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
The commonly used pump-specific-speed expression is based on rotational speed N, discharge Q and head H. The corresponding conventional turbine specific speed is instead based on N, turbine output power P and head H. Both quantities are useful for selecting the general type and proportions of a rotodynamic machine. Their numerical values must be interpreted using the stated unit convention. Therefore Option A is correct.
వివరణ:
Question 3
ప్రశ్న 3
A pump operates at N = 1200 rpm, delivers Q = 0.050 m³/s and develops H = 25 m. Using Ns = N sqrt(Q)/H^(3/4), what is its specific speed?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
The stated expression is Ns = N sqrt(Q)/H^(3/4). Here sqrt(0.050) is approximately 0.22361. Also, 25^(3/4) is approximately 11.180. Thus Ns = 1200 × 0.22361/11.180 = approximately 24.0. Therefore Option B is correct.
వివరణ:
Question 4
ప్రశ్న 4
Which qualitative ordering of rotodynamic pump impeller types with increasing specific speed is generally correct when one consistent convention is used?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
Radial-flow centrifugal impellers are generally associated with relatively lower specific speeds and comparatively higher heads. Mixed-flow designs occupy an intermediate range. Axial-flow pumps handle relatively large discharges at low heads and consequently have higher specific speeds. Exact numerical boundaries vary with the specific-speed convention used. Therefore Option B is correct.
వివరణ:
Question 5
ప్రశ్న 5
For a multistage centrifugal pump having identical stages connected in series, how should conventional pump specific speed be applied?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
In a multistage pump connected in series, essentially the same discharge passes through every stage. The heads developed by the individual stages add to produce the total pump head. Specific speed is intended to characterize the geometry and operating duty of an individual impeller or stage. It is therefore based on the head per stage together with the pump discharge and rotational speed. Hence Option A is correct.
వివరణ:
Question 6
ప్రశ్న 6
For a conventional centrifugal pump operating at fixed rotational speed and impeller diameter, what is the usual trend of its actual head-discharge characteristic over the normal operating range?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
A centrifugal pump has a characteristic relationship between developed head and discharge at a specified rotational speed. For the usual stable centrifugal-pump characteristic, developed head generally decreases as discharge increases. Slip and hydraulic losses influence the exact shape of this curve. The curve must therefore be combined with the system characteristic to determine actual operation. Hence Option A is correct.
వివరణ:
Question 7
ప్రశ్న 7
Which statement best describes the efficiency-discharge characteristic of a normal centrifugal pump operated at constant speed?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
At very low flow, hydraulic and mechanical losses constitute a large fraction of the useful output. As discharge approaches the design region, the flow through the impeller and casing becomes better aligned and efficiency improves. A maximum efficiency occurs at the best-efficiency point, commonly abbreviated BEP. Beyond this region, increasing hydraulic losses and off-design flow cause efficiency to decrease. Therefore Option A is correct.
వివరణ:
Question 8
ప్రశ్న 8
At its best-efficiency operating point, a water pump delivers Q = 0.050 m³/s against a head of 30 m while requiring 20.0 kW of shaft power. What is its overall efficiency? Take rho = 1000 kg/m³ and g = 9.81 m/s².
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
Useful hydraulic output power is rho g Q H. Substitution gives 1000 × 9.81 × 0.050 × 30 = 14715 W, or 14.715 kW. Overall efficiency is useful hydraulic output divided by shaft input. Therefore eta_o = 14.715/20.0 = 0.73575. The efficiency is approximately 73.6 percent, so Option B is correct.
వివరణ:
Question 9
ప్రశ్న 9
For the typical conventional centrifugal-pump performance characteristic considered at fixed speed, what is the usual trend of brake or shaft power as discharge increases?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
Pump shaft-power characteristics depend on impeller design and operating condition. For the conventional centrifugal-pump characteristic normally presented with backward-curved blades, brake power generally increases as discharge increases. This trend is useful when selecting a motor capable of covering the expected operating range. It should not be interpreted as a universal law for every possible rotodynamic impeller geometry. Under the stated conventional characteristic, Option A is correct.
వివరణ:
Question 10
ప్రశ్న 10
What is meant by the shutoff condition of a centrifugal pump?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
Shutoff refers to operation with essentially zero discharge, such as when the delivery valve is completely closed. A centrifugal pump can still develop a finite pressure rise or shutoff head in this condition. Useful hydraulic output power is zero because Q is zero, even though the shaft continues to supply power. Continuous operation at shutoff can produce heating and damaging internal recirculation. Therefore Option A is correct.
వివరణ:
Question 11
ప్రశ్న 11
How is the actual steady operating point of a centrifugal pump connected to a piping system determined?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
The pump provides a head that depends on discharge according to its own characteristic curve. The piping system requires a head consisting of static head and flow-dependent losses. At steady operation, the head produced by the pump must equal the head required by the system at the same discharge. The intersection of the two curves therefore establishes both operating head and operating flow. Hence Option A is correct.
వివరణ:
Question 12
ప్రశ్న 12
A pump characteristic is Hp = 40 - 1000Q² and the connected system characteristic is Hsys = 10 + 1500Q², where H is in metres and Q is in m³/s. What is the operating point approximately?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
At the operating point, pump head equals system head. Thus 40 - 1000Q² = 10 + 1500Q². This gives 30 = 2500Q², so Q² = 0.012 and Q = approximately 0.1095 m³/s. Substituting this value into either characteristic gives H = 28.0 m. Therefore Option B is correct.
వివరణ:
Question 13
ప్రశ్న 13
For a centrifugal pump with a normally downward-sloping H-Q curve, what is the usual effect of partially closing a throttling valve in the delivery line while pump speed remains unchanged?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
Partially closing a delivery valve increases the resistance coefficient of the external piping system. The system head curve therefore rises more steeply with discharge. Its new intersection with a normal downward-sloping pump characteristic occurs at a smaller discharge. Because the pump curve has higher head at the lower discharge, the operating pump head generally increases. Therefore Option A is correct.
వివరణ:
Question 14
ప్రశ్న 14
For the same centrifugal pump operating at dynamically similar corresponding points after a change of rotational speed, which affinity relationships are correct?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
For a fixed impeller diameter operating at corresponding dynamically similar points, the pump affinity laws relate performance to rotational speed. Discharge varies directly with N. Head varies with the square of N because the characteristic velocity varies with speed. Power varies with the cube of N when density and efficiency remain comparable. Therefore Option A is correct.
వివరణ:
Question 15
ప్రశ్న 15
A centrifugal pump operating at 1200 rpm delivers 0.040 m³/s against 20 m head and requires 8.0 kW at a given corresponding operating point. If speed is increased to 1500 rpm and similarity is assumed, what are the new Q, H and P approximately?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
The speed ratio is 1500/1200 = 1.25. The discharge therefore becomes 0.040 × 1.25 = 0.050 m³/s. Head becomes 20 × 1.25² = 31.25 m. Power becomes 8.0 × 1.25³ = 15.625 kW. Therefore Option A is correct.
వివరణ:
Question 16
ప్రశ్న 16
What is the principal purpose of connecting centrifugal pumps in series?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
In a series arrangement, essentially the same flow passes successively through each pump. Each pump contributes an increase in hydraulic head. The combined pump characteristic is obtained by adding the individual heads at a common discharge. Series operation is therefore useful when one pump cannot provide the required system head. Hence Option A is correct.
వివరణ:
Question 17
ప్రశ్న 17
Two identical pumps are connected in series. At Q = 0.040 m³/s, each pump individually develops 18 m of head. Neglecting interaction effects, what combined head do the two pumps develop at this discharge?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
For pumps connected in series, the same discharge passes through both pumps. Their heads are added at that common flow rate. Each pump provides 18 m at Q = 0.040 m³/s. The combined head is therefore 18 + 18 = 36 m. Hence Option C is correct.
వివరణ:
Question 18
ప్రశ్న 18
What is the principal purpose of connecting centrifugal pumps in parallel?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
In parallel operation, the pumps discharge into a common delivery system. At a given common head, the combined discharge is the sum of the individual pump discharges. Parallel arrangements are therefore useful when a greater flow rate is required. The actual increase in system flow depends on the combined pump curve and the system characteristic. Therefore Option A is correct.
వివరణ:
Question 19
ప్రశ్న 19
Two identical pumps operate in parallel. At a head of 15 m, each pump individually delivers 0.030 m³/s. What is the combined discharge at 15 m head according to ideal pointwise curve addition?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
For pumps in parallel, the individual discharges are added at a common head. Each pump delivers 0.030 m³/s at a head of 15 m. The combined discharge at that same head is therefore 0.030 + 0.030. This gives 0.060 m³/s. Hence Option C is correct.
వివరణ:
Question 20
ప్రశ్న 20
Why does adding a second identical pump in parallel not necessarily double the actual system discharge, even though the combined pump curve has twice the discharge at a specified head?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
Pointwise addition of two identical parallel pump curves gives twice the single-pump discharge at any selected common head. However, the piping-system head requirement normally rises as flow increases because friction losses increase. The new combined curve therefore intersects the system curve at a new head as well as a new discharge. As a result, the actual increase in discharge is commonly less than a simple doubling of the original system flow. Therefore Option A is correct.
వివరణ:
Question 21
ప్రశ్న 21
Why is priming necessary before starting an ordinary centrifugal pump that is not self-priming?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
An ordinary centrifugal pump cannot normally develop adequate suction when its casing is filled only with air. Air has a much lower density than the liquid being pumped. Priming fills the pump casing and suction line with liquid and removes trapped air. A foot valve can help retain the priming liquid when the pump is stopped. Therefore Option A is correct.
వివరణ:
Question 22
ప్రశ్న 22
What is the basic mechanism of cavitation damage in a centrifugal pump?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
Pressure is particularly low near the eye of a centrifugal-pump impeller. If the local absolute pressure approaches the liquid vapour pressure, vapour cavities can form. These cavities are carried into regions where pressure subsequently rises. Their rapid collapse can cause noise, vibration, pitting and deterioration of pump performance. Therefore Option A is correct.
వివరణ:
Question 23
ప్రశ్న 23
Which statement correctly distinguishes NPSH available and NPSH required for a centrifugal pump?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
NPSH available is determined by the suction-system conditions, including absolute pressure, elevation, suction losses and liquid vapour pressure. NPSH required is a property of the particular pump at a specified speed and discharge and is normally established by testing or manufacturer data. The available value must exceed the required value for satisfactory cavitation performance. Practical designs normally include an additional margin rather than relying on equality. Therefore Option A is correct.
వివరణ:
Question 24
ప్రశ్న 24
A centrifugal pump draws water from an open reservoir. Atmospheric pressure head is 10.3 m of water, vapour-pressure head is 0.3 m, the pump centreline is 4.0 m above the reservoir surface and suction-pipe losses are 1.0 m. Using NPSHa = Ha - Hv - Hs - hfs, what are the available NPSH and the margin if NPSHr = 3.5 m?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
For the stated open-reservoir installation, NPSHa = Ha - Hv - Hs - hfs. Substitution gives 10.3 - 0.3 - 4.0 - 1.0 = 5.0 m. The required NPSH is 3.5 m. The available margin is therefore 5.0 - 3.5 = 1.5 m. Hence Option B is correct.
వివరణ:
Question 25
ప్రశ్న 25
Consider the following statements concerning centrifugal-pump cavitation and suction design: I. Increasing liquid temperature usually raises vapour pressure and therefore reduces NPSHa if other conditions remain unchanged. II. Reducing suction lift increases NPSHa. III. Reducing friction losses in the suction line increases NPSHa. IV. NPSHr generally depends on the particular pump and its operating point. Which option is correct?
Select an option first. || ముందుగా ఒక సమాధానాన్ని ఎంచుకోండి.
Explanation:
Statement I is correct because a higher vapour-pressure head subtracts from the available suction margin. Statement II is correct because lowering the pump relative to the liquid surface increases the suction pressure available at the pump. Statement III is correct because lower suction-line head loss leaves more total head available above vapour pressure. Statement IV is correct because required NPSH is associated with pump design, speed and operating flow rather than being a universal constant. Therefore all four statements are correct and Option D is the valid answer.
వివరణ:
Answer Key సమాధానాల పట్టిక
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Question 1 ప్రశ్న 1Answer: A. The speed of a geometrically similar pump that would deliver unit discharge against unit head సమాధానం: A.
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Question 2 ప్రశ్న 2Answer: A. Pump specific speed uses discharge Q, whereas turbine specific speed conventionally uses output power P సమాధానం: A.
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Question 3 ప్రశ్న 3Answer: B. 24.0 సమాధానం: B.
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Question 4 ప్రశ్న 4Answer: B. Radial-flow, mixed-flow, axial-flow సమాధానం: B.
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Question 5 ప్రశ్న 5Answer: A. It should be based on the performance of one stage, using the discharge through the pump and the head developed per stage సమాధానం: A.
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Question 6 ప్రశ్న 6Answer: A. Head generally decreases as discharge increases సమాధానం: A.
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Question 7 ప్రశ్న 7Answer: A. Efficiency normally rises from low-flow conditions, reaches a maximum at the best-efficiency point and then decreases సమాధానం: A.
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Question 8 ప్రశ్న 8Answer: B. 73.6% సమాధానం: B.
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Question 9 ప్రశ్న 9Answer: A. It generally increases with discharge over the normal characteristic సమాధానం: A.
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Question 10 ప్రశ్న 10Answer: A. The delivery valve is closed so discharge is zero while the pump develops a finite shutoff head సమాధానం: A.
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Question 11 ప్రశ్న 11Answer: A. By the intersection of the pump head-discharge curve and the system head-discharge curve సమాధానం: A.
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Question 12 ప్రశ్న 12Answer: B. Q = 0.1095 m³/s and H = 28 m సమాధానం: B.
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Question 13 ప్రశ్న 13Answer: A. System resistance increases and the operating point generally moves to lower discharge and higher pump head సమాధానం: A.
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Question 14 ప్రశ్న 14Answer: A. Q is proportional to N, H is proportional to N² and P is proportional to N³ సమాధానం: A.
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Question 15 ప్రశ్న 15Answer: A. 0.050 m³/s, 31.25 m and 15.63 kW సమాధానం: A.
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Question 16 ప్రశ్న 16Answer: A. To obtain a greater total head, with the individual pump heads added at the same discharge సమాధానం: A.
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Question 17 ప్రశ్న 17Answer: C. 36 m సమాధానం: C.
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Question 18 ప్రశ్న 18Answer: A. To obtain a greater combined discharge by adding the individual pump discharges at the same head సమాధానం: A.
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Question 19 ప్రశ్న 19Answer: C. 0.060 m³/s సమాధానం: C.
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Question 20 ప్రశ్న 20Answer: A. Because the actual operating point must be found from the intersection of the combined pump curve with the system curve, whose required head usually increases with discharge సమాధానం: A.
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Question 21 ప్రశ్న 21Answer: A. The casing and suction pipe must be filled with liquid and air removed so the impeller can establish the required suction pressure difference సమాధానం: A.
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Question 22 ప్రశ్న 22Answer: A. Local pressure falls to or below vapour pressure, vapour cavities form and then collapse violently when carried into higher-pressure regions సమాధానం: A.
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Question 23 ప్రశ్న 23Answer: A. NPSHa is supplied by the installation, whereas NPSHr is a pump-specific requirement at the operating condition; satisfactory design requires NPSHa to exceed NPSHr with an appropriate margin సమాధానం: A.
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Question 24 ప్రశ్న 24Answer: B. NPSHa = 5.0 m and margin = 1.5 m సమాధానం: B.
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Question 25 ప్రశ్న 25Answer: D. I, II, III and IV సమాధానం: D.