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Chapter 8

Pumps for Water Wells [4 Hours]

Pumps ~10+ Past Questions

MOST IMPORTANT TOPICS & MARKS DISTRIBUTION

High-Yield Topics (by exam frequency):

  1. Types of pumps used for groundwater lifting — Asked in 2071, 2073 [4 marks]
  2. Centrifugal pump — working principle, advantages, limitations — Asked in 2072 Ashwin, 2072 Magh [4–6 marks]
  3. Factors in pump selection — well depth, yield, TDH — Asked in 2078, 2073 [2–4 marks]

Marks Each Time Asked:

ExamQuestionsTotal
2078 ChaitraQ6 [4]4
2073 BhadraQ9 [4+2]6
2072 AshwinQ9 [4+2]6
2072 MaghQ9 [4]4
2071 BhadraQ9 [4]4

CHAPTER ROADMAP

  1. Introduction — need for pumping
  2. Classification of pumps
  3. Centrifugal pump — working principle
  4. Submersible pump
  5. Jet pump (ejector pump)
  6. Airlift pump
  7. Reciprocating pump (hand pump)
  8. Comparison of groundwater pumps
  9. Factors in pump selection
  10. Past question bank for Chapter 8
  11. Chapter summary and exam key points

8.1 INTRODUCTION — NEED FOR PUMPING

Groundwater, by nature, exists below the land surface. To extract it for use in drinking water supply, irrigation, or industrial purposes, energy must be supplied to lift the water from the aquifer to the surface. This energy is typically provided by pumps.

The selection and design of a pumping system is a critical step in groundwater development. The pump must:

  • Deliver the required discharge (Q) at the required pressure head
  • Overcome the total dynamic head (TDH), which includes the static lift, drawdown, friction losses, and delivery head
  • Operate efficiently at the design point to minimize energy costs
  • Be suitable for the well type, depth, and water quality conditions
Key Exam Point: This is a theory-only chapter — no numerical problems. Questions typically ask for types of pumps (4 marks), working principle of centrifugal pump (4 marks), or pump selection factors (4 marks). Focus on clear descriptions with diagrams.

8.2 CLASSIFICATION OF PUMPS

PAST EXAM QUESTIONS ADDRESSED:

2071 Bhadra Q9 [4]: What are the types of pumps used for lifting water?

2073 Bhadra Q9 [4+2]: Describe briefly any four common groundwater pumps.

Pumps used for groundwater lifting can be classified based on their working principle:

Classification of Groundwater Pumps GROUNDWATER PUMPS ROTODYNAMIC (KINETIC) 1. Centrifugal pump • Volute type • Turbine (diffuser) type 2. Submersible pump (motor + pump submerged) 3. Jet pump (ejector) POSITIVE DISPLACEMENT 4. Reciprocating pump • Suction type • Force (lift) type 5. Hand pump (India Mark II, etc.) • Deep well / shallow well SPECIAL TYPES 6. Airlift pump (compressed air) 7. Hydraulic ram (water hammer energy) 8. Solar pump (PV-powered submersible) Most asked in IOE: Centrifugal pump (principle) + Submersible pump + Selection factors When asked “list types,” name at least 5–6 types with one-line description each. When asked “describe four pumps,” write 4–5 lines each with sketch.
Figure 8.1: Classification of pumps used for groundwater lifting.

8.3 CENTRIFUGAL PUMP — WORKING PRINCIPLE

PAST EXAM QUESTIONS ADDRESSED:

2072 Ashwin Q9 [4+2]: Explain the working principle, advantages, and limitations of the centrifugal pump used for groundwater.

2072 Magh Q9 [4]: Explain the working principle of the centrifugal pump used for lifting groundwater.

8.3.1 Description

The centrifugal pump is the most widely used type of pump for groundwater lifting. It belongs to the rotodynamic pump category and works on the principle of converting kinetic energy of water into pressure energy.

8.3.2 Main Components

  • Impeller: A rotating disc with curved vanes (blades) mounted on a shaft. It is the key component that imparts energy to the water. May be open, semi-open, or enclosed (shrouded) type.
  • Casing (volute): A spiral-shaped housing that surrounds the impeller. Its cross-sectional area gradually increases from the impeller to the discharge nozzle, converting kinetic energy to pressure energy.
  • Suction pipe with foot valve and strainer: Connects the pump to the water source. The foot valve prevents backflow when the pump is stopped. The strainer prevents debris from entering.
  • Delivery pipe: Carries water from the pump to the point of use or storage.
  • Shaft and bearings: The shaft connects the impeller to the prime mover (motor or engine). Bearings support the shaft.
  • Stuffing box / mechanical seal: Prevents leakage where the shaft passes through the casing.
Centrifugal Pump — Cross Section Delivery Impeller ω Suction (eye) Shaft Seal Volute casing (area expands) Energy conversion: Impeller: KE ↑ (velocity) Volute: KE → PE (pressure)
Figure 8.3b: Centrifugal pump cross-section — impeller vanes throw water outward; expanding volute converts velocity to pressure head.

8.3.3 Working Principle

The working principle of a centrifugal pump can be explained in the following steps:

  1. Priming: Before starting, the pump casing and suction pipe must be completely filled with water (primed). Air must be removed because the pump cannot create sufficient vacuum to lift water if air is present.
  2. Rotation of impeller: When the electric motor (or engine) starts, the impeller rotates at high speed (typically 1450 or 2900 rpm).
  3. Centrifugal action: As the impeller rotates, the water between the vanes is thrown outward by centrifugal force towards the periphery of the casing. This creates a region of low pressure (partial vacuum) at the centre of the impeller (eye).
  4. Suction: Due to the low pressure at the eye, atmospheric pressure acting on the water surface in the source (well/sump) pushes water up through the suction pipe into the impeller eye. This is a continuous process as long as the pump runs.
  5. Energy conversion in the volute: The water thrown to the periphery at high velocity enters the volute casing. As the cross-sectional area of the volute increases, the velocity of water decreases and its pressure increases (Bernoulli’s principle). This converts kinetic energy into pressure energy.
  6. Delivery: The high-pressure water exits through the delivery pipe to the required height or storage tank.
Working Principle of a Centrifugal Pump Delivery Eye ω Foot valve Strainer Water level in well Volute casing (area increases → velocity ↓, pressure ↑) Impeller (rotating vanes) Suction KE (impeller → high velocity) → PE (volute → high pressure) → Delivered at required head
Figure 8.2: Schematic of a centrifugal pump showing impeller, volute casing, suction pipe with foot valve, and delivery pipe.
Animated: How a Centrifugal Pump Works Volute (area increases →) Eye Foot Valve Strainer Well / Sump Delivery MOTOR ω SUCTION Impeller (rotating) ① Low P at eye → suction    ② Centrifugal force → high velocity    ③ Volute → KE converts to PE → delivery
Figure 8.2b: Animated centrifugal pump — water particles (blue dots) show the flow path: suction into eye → radially outward through spinning impeller → into volute → up the delivery pipe. The impeller vanes rotate continuously.

8.3.4 Types of Centrifugal Pumps

(a) Volute Pump

The most common type. The impeller is surrounded by a spiral volute casing that converts velocity head to pressure head. Simple construction and widely used for surface-mounted installations.

Types of Centrifugal Pumps Radial Flow Flow ⊥ to shaft axis High head, low Q Ns: 500–4000 Deep wells, high- pressure systems Mixed Flow Radial + axial components Medium head & Q Ns: 4000–10000 Irrigation pumps, medium-depth wells Axial Flow Flow ∥ to shaft axis Low head, high Q Ns: > 10000 Flood pumps, drainage, lift stations Ns = N√Q / H3/4 — specific speed determines pump type selection
Figure 8.3c: Three types of centrifugal pumps classified by flow direction and specific speed — radial for high head, axial for high discharge.

(b) Turbine (Diffuser) Pump / Deep-Well Vertical Turbine Pump

Uses stationary guide vanes (diffusers) around the impeller instead of a volute casing. The diffuser vanes gradually expand the flow area and convert kinetic energy more efficiently. Used in vertical turbine pumps installed in deep wells (also called deep-well turbine pumps or lineshaft turbine pumps).

Main Components:

ComponentFunction
MotorProvides power; mounted at ground level
Line shaftTransmits rotational power from motor to pump bowls deep in the well
Column pipeCarries water upward from pump to surface discharge
Pump bowlsMultiple impeller-diffuser stages that increase pressure
Suction bellAllows water entry at the bottom of the pump assembly

Advantages:

  • High efficiency for deep wells
  • Motor remains at ground level for easy maintenance and inspection
  • Can handle large discharge rates
  • Long service life with proper maintenance

Limitations:

  • High initial and installation cost
  • Requires skilled installation and precise shaft alignment
  • Not suitable for small-discharge systems
  • Performance affected by sandy or corrosive water

Applications: Deep tube wells, large-scale irrigation projects, municipal water supply, and industrial water extraction.

(c) Multistage Centrifugal Pump

Contains two or more impellers arranged in series on the same shaft. Each impeller (stage) adds pressure. Used when a single impeller cannot provide the required total head. The total head = head per stage × number of stages.

Multistage Centrifugal Pump — Stages in Series Suction STAGE 1 P₁ = +H STAGE 2 P₂ = +2H STAGE 3 P₃ = +3H . . . STAGE N PN = +N×H Delivery (high P) Pressure builds progressively: H → 2H → 3H → ... → N×H Total Head = H per stage × Number of stages (N) Used in deep-well turbine & submersible pumps (5–30 stages)
Figure 8.2d: Multistage centrifugal pump — impellers in series on a common shaft, each stage adding pressure H. The growing red dot along the pressure bar shows cumulative pressure buildup. All impellers rotate simultaneously.

8.3.5 Advantages and Limitations

Advantages:
  • Simple construction and compact design
  • Smooth, continuous flow (non-pulsating)
  • Can handle large discharges
  • High efficiency (60–85%)
  • Low maintenance cost
  • Can be directly coupled to electric motor
  • Suitable for a wide range of heads and discharges
Limitations:
  • Requires priming before start-up (not self-priming)
  • Limited suction lift (≤ 6–7 m due to atmospheric pressure limit and NPSH requirements)
  • Efficiency drops significantly at off-design conditions
  • Not suitable for very high heads with single stage
  • Cannot handle viscous fluids or fluids with large solids
  • Susceptible to cavitation if NPSH is insufficient
Cavitation: When the pressure at the pump inlet drops below the vapour pressure of water, dissolved gases form bubbles that implode violently when they reach higher-pressure zones. This causes pitting damage to the impeller and noise. To prevent cavitation, the available Net Positive Suction Head (NPSH) must exceed the required NPSH of the pump.
Cavitation and Priming — Visual Explanation WHY PRIMING IS NEEDED Before Priming (FAILS) AIR inside (too light to create sufficient vacuum) After Priming (WORKS) WATER inside (centrifugal force creates vacuum at eye) Fill with water Maximum Suction Lift ≤ 6–7 m Atmospheric pressure = 10.33 m of water Minus: vapour pressure (~0.24 m at 20°C) Minus: friction losses (~2–3 m) Practical limit ≈ 6–7 m 10.33 m (atm pressure) 0.24 m (vapour P) ~3 m (friction & losses) ≈ 7 m (usable suction) CAVITATION PROCESS ① Pressure drops below vapour pressure At pump inlet (eye) when suction lift is too high or pipe has excessive friction ② Vapour bubbles form Water boils at low pressure → gas bubbles ③ Bubbles implode violently When bubbles reach high-pressure zones → micro-jets impact impeller surface ④ DAMAGE to impeller Pitting, erosion, noise, vibration Reduced efficiency, eventual failure PREVENTION Keep suction lift within limits (≤ 6–7 m) NPSHavailable > NPSHrequired Minimize pipe friction losses on suction side
Figure 8.2c: Left: Why priming is required — air cannot create sufficient vacuum; only water can. Maximum suction lift ≈ 6–7 m. Right: Cavitation process — pressure drops below vapour pressure → bubbles form → implode violently → impeller damage. Animated bubbles show formation and collapse.

8.4 SUBMERSIBLE PUMP

A submersible pump is a centrifugal pump that has the motor and pump unit integrated into a single waterproof, sealed assembly that is lowered entirely into the well below the water level.

8.4.1 Construction

  • Motor: Hermetically sealed, water-cooled electric motor located below the pump stages. The motor is filled with oil or water for insulation and cooling.
  • Pump stages: Multiple impellers (stages) stacked in series above the motor. Each stage adds head. A typical groundwater submersible may have 5–30 stages.
  • Intake screen: Between the motor and pump section, allows water to enter while filtering sand.
  • Power cable: Waterproof electrical cable runs from the motor to the surface control panel.
  • Drop pipe (rising main): Connects the pump outlet to the surface delivery.

8.4.2 Working Principle

The working principle is the same as a multistage centrifugal pump. The motor drives the impellers, which spin and throw water outward by centrifugal force. Each stage adds pressure, and the accumulated pressure forces water up through the rising main to the surface.

Reciprocating Pump — Mechanism Piston Crank Suction valve Delivery valve From source L (stroke) Q = ALN/60 (single-acting) Q = 2ALN/60 (double-acting)
Figure 8.4b: Reciprocating pump mechanism — crank rotation drives piston for alternating suction and delivery strokes with one-way valves.

Because the pump is submerged, it does not need priming and there is no suction lift limitation. The pump is always below the water level, so it pushes water upward rather than pulling it.

8.4.3 Advantages and Limitations

Advantages:
  • No priming needed — always submerged
  • No suction lift limit — can lift from any depth
  • Compact — fits inside small-diameter tube wells
  • Quiet operation (submerged, no surface noise)
  • No separate pump house required
  • High efficiency for deep-well applications
  • Freeze-proof (pump is below frost line)
Limitations:
  • Higher initial cost than surface pumps
  • Difficult to inspect and repair (must be pulled out)
  • Motor burns out if water level drops below the motor (dry running)
  • Sensitive to sand and abrasive particles
  • Electrical cable failure is difficult to detect
  • Motor winding insulation can degrade over time
Submersible Pump in a Tube Well Static WL Pumping WL Drawdown Rising main Power cable PUMP (multi-stage) Intake screen MOTOR (sealed, water- cooled) Q (discharge) Check valve Pump always below water level → no priming needed
Figure 8.3: Submersible pump installed in a tube well showing motor, pump stages, intake screen, rising main, and power cable.
Animated: Submersible Pump in Operation Ground Surface Static WL Pumping WL Drawdown Q (discharge) Power cable PUMP (multi-stage impellers) Intake screen MOTOR (sealed, water- cooled) Check valve Rising main Well screen KEY ADVANTAGE Pump always below water → No priming needed, any depth! GW inflow GW inflow Motor drives multi-stage impellers → water rises through stages → accumulated pressure pushes water up rising main to surface
Figure 8.3b: Animated submersible pump in operation — blue particles show water entering through the intake screen, passing through the multi-stage pump, and rising through the delivery pipe. The motor pulses to indicate rotation.

8.5 JET PUMP (EJECTOR PUMP)

A jet pump (or ejector pump) combines a centrifugal pump at the surface with a jet (ejector) assembly located down in the well. It is used to lift water from depths greater than the normal suction limit of a surface centrifugal pump (which is about 6–7 m). The jet pump operates on the Venturi effect: when a fluid flows through a constricted nozzle, its velocity increases and its static pressure drops, creating suction that draws in surrounding water.

8.5.1 Components

The jet pump consists of four critical parts:

Submersible Pump — Key Features Multi-stage pump Impellers stacked Submersible motor Sealed, water-cooled Riser pipe → surface Power cable from surface Advantages No priming needed No suction limit Quiet operation Deep wells (> 50 m) High heads possible Limitations Difficult to service Motor seal failures Higher initial cost Motor + pump submerged below water level in the well Most common pump type for deep tube wells in Nepal
Figure 8.5b: Submersible pump — motor and multi-stage pump unit are both submerged in the well, eliminating suction head limitations.
  1. Nozzle: Converts the pressure energy of the power fluid into high-velocity kinetic energy.
  2. Suction chamber: The area where the vacuum is formed and groundwater enters.
  3. Mixing tube (throat): A cylindrical section where the two fluids exchange momentum and reach a uniform velocity.
  4. Diffuser: A divergent section that recovers pressure before discharge.

8.5.2 Types of Jet Pumps

(a) Single-Pipe Jet Pump: Best for shallow wells with water levels up to about 25 feet (7.5 m) deep. Uses one suction pipe, and the jet assembly (Venturi and nozzle) is built directly into the pump housing above ground. It relies primarily on suction created by the pump.

(b) Double-Pipe Jet Pump: Designed for deeper wells, typically 25–110 feet (7.5–33 m). Uses two pipes: a pressure pipe pushes water down into the well, and a suction (return) pipe pulls water back up. The jet assembly is placed down in the well. Water is forced down the pressure pipe through the submerged jet to create a vacuum, which helps push more water up through the return pipe.

The choice of type depends on the vertical distance to the water table and the required discharge head.

8.5.3 Working Principle

  1. A centrifugal pump at the surface sends a portion of the pumped water back down through a pressure pipe to the ejector assembly in the well.
  2. The ejector has a nozzle that converts the pressure energy of this recirculated water into a high-velocity jet.
  3. The high-velocity jet creates a low-pressure zone (Venturi effect) in the mixing chamber, which draws groundwater from the well into the jet stream.
  4. The mixed water (recirculated + fresh groundwater) passes through a diffuser (gradually expanding section), converting velocity to pressure.
  5. The pressurized mixture rises through the return pipe to the surface pump, which delivers the net discharge.

8.5.4 Advantages, Limitations, and Suitability

Animated: How a Jet Pump (Ejector) Works CENTRIFUGAL PUMP Electric Motor GROUND Pressure Pipe (↓) Return Pipe (↑) Net Q (delivery) EJECTOR Nozzle Mixing chamber Low P zone Diffuser (V↓, P↑) GW inflow Water Level How the Jet Pump Cycle Works ① Surface pump pressurizes water A portion sent DOWN the pressure pipe ② Nozzle creates high-velocity jet Pressure energy → Kinetic energy ③ Venturi effect — low pressure zone Draws surrounding groundwater into the mixing chamber ④ Diffuser converts KE back to PE Velocity ↓, Pressure ↑ (Bernoulli) ⑤ Mixed water rises to surface Through return pipe → pump delivers net Q [!] Low Efficiency: 25–40% Part of pumped water is recirculated Net Q = total pumped − recirculated Suitable depth: 20 – 60 m All moving parts at surface → easy maintenance
Figure 8.5: Animated jet pump (ejector) — red dots show pressurized water flowing down through the nozzle; blue dots show the mixed water (recirculated + fresh GW) returning to the surface. The pulsing circle at the nozzle shows the low-pressure (Venturi) zone that draws in groundwater.
Advantages:
  • All moving parts at the surface — easy maintenance without pulling the pipe string
  • Can lift water from 20–60 m depth
  • Self-priming capability — can clear air from suction lines automatically
  • Suitable for small-diameter boreholes (slim profile fits narrow casings)
Limitations:
  • Low efficiency (25–40%) due to energy loss in the jet
  • Part of the pumped water is recirculated (reduced net discharge)
  • Efficiency decreases with increasing depth
  • Not suitable for large yields or very high-yield aquifers

8.5.5 Suitability

Jet pumps are particularly suitable in the following conditions:

  • Abrasive environments: Because there are no submerged moving parts, jet pumps are well-suited for wells containing sand, silt, or muddy water that would otherwise erode mechanical seals in submersible pumps.
  • Corrosive conditions: The jet assembly can be manufactured from non-corrosive materials (plastic or bronze), making them ideal for pumping contaminated or chemically aggressive groundwater.
  • Small-diameter boreholes: Their slim profile allows installation in very narrow casings where other pumps might not fit.
  • Fluctuating water levels: Can operate reliably in areas with fluctuating groundwater levels.
  • Remote or low-maintenance sites: Since the motor and electrical components remain at the surface, repair and servicing is straightforward.

8.6 AIRLIFT PUMP

An airlift pump uses compressed air to lift water from a well. It has no moving parts inside the well.

8.6.1 Working Principle

  1. Compressed air is injected into the bottom of a riser pipe (eductor pipe) submerged in the well water.
  2. The air mixes with water in the riser pipe, creating an air-water mixture that is lighter than the surrounding water column.
  3. The denser surrounding water pushes the lighter air-water mixture upward through the riser pipe to the surface.
  4. At the surface, air is separated and water is collected.

The key requirement is that the submergence ratio (ratio of the submerged length of the riser pipe to the total length above the water surface) must be adequate. Typically, the submergence should be 50–70% of the total riser length for reasonable efficiency.

Animated: How an Airlift Pump Works Ground Surface AIR COMPRESSOR Air Pipe (compressed air ↓) Water Level Submergence (S) Lift (L) Air injection point Q (water + air) (air separates at surface) Riser Pipe (Eductor) Working Principle Air + water mixture inside riser is LIGHTER than surrounding pure water column → buoyancy lifts mixture upward! Submergence Ratio S/(S+L) = 50–70% for reasonable efficiency Efficiency: 20–35% No moving parts in well! Compressed air → bubbles mix with water in riser → lighter column rises → denser surrounding water pushes mixture up → water delivered at surface
Figure 8.6: Animated airlift pump — white bubbles (air) rise through the riser pipe, carrying water (blue dots) upward. The air-water mixture is lighter than the surrounding water column, creating the lifting force. The pulsing red dot shows the air injection point.

8.6.2 Advantages and Limitations

Advantages:
  • No moving parts in the well — minimal wear
  • Can handle sandy or muddy water
  • Useful for well development and testing
  • Simple installation
Limitations:
  • Very low efficiency (20–35%)
  • Requires large submergence — not suitable for shallow wells
  • Requires air compressor at the surface
  • Not suitable for continuous large-scale pumping

8.7 RECIPROCATING PUMP (HAND PUMP)

A reciprocating pump is a positive displacement pump that uses a piston or plunger moving back and forth in a cylinder to draw and push water. Hand-operated versions are widely used in rural areas of Nepal and South Asia for shallow groundwater extraction.

8.7.1 Working Principle

Animated: How a Reciprocating (Hand) Pump Works SUCTION STROKE (Piston moves UP) Handle Delivery valve (on piston) Suction valve (at bottom) Well water Water enters ↑ Vacuum created below piston Suction valve: OPEN Delivery valve: CLOSED DELIVERY STROKE (Piston moves DOWN) Delivery valve OPENS ↑ Suction valve CLOSED Spout Well water Suction valve: CLOSED Delivery valve: OPEN Complete Cycle: UP stroke → vacuum below piston → suction valve opens → water enters  |  DOWN stroke → water forced through piston valve → delivered via spout
Figure 8.7: Animated reciprocating (hand) pump — Left: Suction stroke (piston up, suction valve opens, water drawn in). Right: Delivery stroke (piston down, delivery valve opens, water pushed through and out the spout). Valves alternate green (open) / red (closed).
  1. Suction stroke: As the piston moves upward, the volume below the piston increases, creating a partial vacuum. The suction valve opens and water from the well enters the cylinder.
  2. Delivery stroke: As the piston moves downward, the suction valve closes and the delivery valve (on the piston) opens. Water is forced above the piston.
  3. On the next upstroke, the water above the piston is pushed out through the delivery spout, and fresh water enters from below.

8.7.2 Types of Hand Pumps

Type Depth Range Example Features
Shallow well hand pump < 7 m (suction type) No. 6 pump Cylinder at surface; suction lift limited to ~7 m
Medium-depth hand pump 7 – 15 m Tara pump Direct-action; cylinder below water level
Deep well hand pump 15 – 45 m India Mark II, India Mark III, Afridev Cylinder below water level with connecting rod; robust, widely used
Extra deep well 45 – 90 m India Mark III (modified) Uses lighter components and VLOM design
Hand Pump Types for Different Well Depths Shallow Well Depth: < 15 m Suction type Cylinder above ground Examples: No. 6, Tara pump Easy maintenance Medium Depth Depth: 15-45 m Force/direct action type Cylinder below ground Examples: India Mark II, Afridev Most common in Nepal Deep Well Depth: > 45 m Open-top cylinder Deep-set mechanism Examples: India Mark III, Vergnet Complex maintenance Suction limit ≈ 7 m (atmospheric) — deeper wells need downhole cylinders
Figure 8.7c: Hand pump classification by well depth — shallow (<15m, suction), medium (15-45m, force/direct), and deep (>45m, open-top cylinder).
Key Exam Point: In Nepal, the most commonly installed hand pump for community water supply in the Terai is the India Mark II deep well hand pump, which can operate at depths up to 45 m. The Afridev pump is popular because of its VLOM (Village Level Operation and Maintenance) design.

8.7.3 Advantages and Limitations (slide)

Advantages:

  • No electricity or fuel required — operates on manual power
  • Low initial and operating cost
  • Simple construction — easy to operate and understand
  • Suitable for rural/remote areas without power supply
  • Can be maintained at village level (VLOM design — Afridev, India Mark III)
  • No priming required (deep-well types with submerged cylinder)

Limitations:

  • Very low discharge — only suitable for domestic/drinking water, not irrigation
  • Physically demanding — requires continuous manual effort
  • Suction type limited to ~7 m depth (atmospheric pressure constraint)
  • Pulsating (intermittent) flow, not continuous
  • Wear of piston seals, valves, and connecting rods requires periodic replacement
  • Deep-well types require pulling the riser pipe for cylinder maintenance

8.8 COMPARISON OF GROUNDWATER PUMPS

PAST EXAM QUESTION ADDRESSED:

2073 Bhadra Q9 [4+2]: Describe briefly any four common groundwater pumps.

Feature Centrifugal (Surface) Deep-Well Vertical Turbine Submersible Jet Pump Airlift Hand Pump
Depth range ≤ 6–7 m (suction) 30–300+ m Up to 300+ m 20–60 m 20–100 m Up to 45 m
Efficiency 60–85% 75–90% 55–80% 25–40% 20–35% 40–60%
Discharge High Large Medium to high Low to medium Low to medium Very low
Priming Required Not needed Not needed Initial prime only Not needed May need
Maintenance Easy (surface) Motor at surface; bowls need pulling Difficult (pull out) Easy (surface parts) Easy (no moving parts) Moderate
Power source Electric / diesel Electric / diesel Electric Electric Air compressor Manual
Cost Low to medium High Medium to high Medium Medium Low
Best suited for Open wells, sumps Deep tube wells, irrigation, municipal supply Deep tube wells Domestic wells, abrasive/corrosive water Well development, testing Rural community supply

8.9 FACTORS IN PUMP SELECTION

PAST EXAM QUESTIONS ADDRESSED:

2078 Chaitra Q6 [4]: Explain the factors to be considered in the selection of pump sets for groundwater pumping.

2073 Bhadra Q9 [4+2]: What factors should be considered while selecting a groundwater pump?

The selection of an appropriate pump for a groundwater project involves the following factors:

Need for Proper Pump Selection: Incorrect pump selection may lead to excessive power consumption, low discharge, damage to the well and pump, and uneconomical operation. Proper selection ensures efficient lifting, economical operation, and long service life of both the pump and the well (Raghunath, 2006).

A. Well Characteristics

  • Well type: Open well or tube well? Open wells typically use centrifugal surface pumps; tube wells need submersible or deep-well turbine pumps.
  • Well depth and casing diameter: The pump must physically fit inside the well. Submersible pumps require minimum 100 mm (4″) casing.
  • Static water level and drawdown: Determines the total pumping lift. If static water level is within 6–7 m, a surface centrifugal pump suffices. Deeper water levels require submersible or jet pumps.
Pump Selection — Decision Factors Pump Selection Well Properties Depth, diameter, available drawdown Q & H Required Design discharge, total head (TDH) Power Source Electricity, diesel, solar, manual Water Quality Sand content, corrosivity Economics Capital cost, O&M, lifecycle Match pump type to operating point (Q, H) on pump characteristic curve Submersible: deep wells | Centrifugal: shallow, high Q | Hand pump: rural, no electricity Always check: duty point falls within high-efficiency range of the pump curve
Figure 8.8b: Pump selection decision tree — well properties, required Q and H, power availability, water quality, and economics all influence the choice.

B. Required Discharge and Head

  • Design discharge (Q): The pump must deliver the required flow rate. Centrifugal pumps handle high Q; hand pumps are for low Q. The selected pump discharge must not exceed the safe yield of the well, otherwise excessive drawdown occurs, well efficiency reduces, and aquifer depletion may happen. Therefore, pump capacity should be slightly less than or equal to the well yield.
  • Total dynamic head (TDH): The sum of:
    • Static suction lift (depth to pumping water level)
    • Static delivery head (height above pump to delivery point)
    • Friction losses in pipes and fittings
    • Velocity head at discharge

C. Power Source Availability

  • Electricity: Most pumps (centrifugal, submersible) require reliable electric supply
  • Diesel/petrol engine: Used where electricity is unavailable or unreliable
  • Solar energy: Increasingly used for submersible pumps in remote areas
  • Manual power: Hand pumps for areas without any power source

D. Water Quality and Sand Content

  • Sandy or turbid water can damage centrifugal pump impellers due to abrasion
  • Corrosive water (high iron, low pH) requires stainless steel or plastic components
  • Airlift pumps are preferred for sandy wells (no submerged moving parts)

E. Economic Factors

  • Initial cost: Purchase and installation cost of the pump set
  • Operating cost: Energy consumption, which depends on pump efficiency and hours of operation
  • Maintenance cost: Ease and frequency of repairs
  • Life cycle cost: Total cost over the expected lifespan (typically 10–20 years)

F. Reliability and Serviceability

  • Availability of spare parts and local repair expertise
  • Durability and expected service life
  • Ease of installation, removal, and repair
  • For community water supply, VLOM (Village Level Operation and Maintenance) pumps are preferred

G. Duty Conditions

  • Continuous vs. intermittent operation: Submersible pumps are well-suited for continuous operation; hand pumps are for intermittent use.
  • Future expansion: Whether the system may need higher discharge in the future
Exam writing strategy: When asked about pump selection factors, organize your answer under clear headings (Well Characteristics, Discharge & Head, Power, Water Quality, Economics, Serviceability). Write 1–2 bullet points under each heading. This structured approach scores higher marks than a loose list.

8.10 PAST QUESTION BANK FOR CHAPTER 8

2078 Chaitra Q6 4 marks

Explain the factors to be considered in the selection of pump sets for groundwater pumping.

ANSWER GUIDE:

Organize under headings: (a) Well characteristics (type, depth, diameter), (b) Discharge & head requirements, (c) Power source availability, (d) Water quality & sand content, (e) Economic factors (initial + operating cost), (f) Reliability & serviceability. Write 1–2 points under each for 4 marks. See Section 8.9.

2073 Bhadra Q9 4+2 marks

Describe briefly any four common groundwater pumps. What factors should be considered while selecting a groundwater pump?

ANSWER GUIDE:

Part 1 (4 marks): Describe four pumps: (1) Centrifugal — principle, volute, priming required; (2) Submersible — motor+pump submerged, no priming; (3) Jet pump — ejector principle, surface pump + down-well nozzle; (4) Hand pump — reciprocating, for rural areas. Write 3–4 lines each. Sections 8.3–8.7.

Part 2 (2 marks): List 4–5 selection factors: well depth, Q & TDH, power availability, water quality, cost. Section 8.9.

2072 Ashwin Q9 4+2 marks

Explain the working principle, advantages, and limitations of the centrifugal pump used for groundwater.

ANSWER GUIDE:

Working principle (4 marks): Priming → impeller rotation → centrifugal force throws water outward → low pressure at eye → suction → volute converts KE to PE → delivery. Include labelled sketch (Figure 8.2). Section 8.3.3.

Advantages & limitations (2 marks): Advantages: simple, continuous flow, high efficiency. Limitations: needs priming, suction lift limited to ~7 m, cavitation risk. Section 8.3.5.

2072 Magh Q9 4 marks

Explain the working principle of the centrifugal pump used for lifting groundwater.

ANSWER GUIDE:

Explain the 6-step working principle: priming, impeller rotation, centrifugal force, suction, energy conversion in volute, delivery. Draw and label Figure 8.2. Section 8.3.3.

2071 Bhadra Q9 4 marks

What are the types of pumps used for lifting water?

ANSWER GUIDE:

Draw the classification chart (Figure 8.1). List all pump types under three categories: (a) Rotodynamic — centrifugal (volute, turbine, multistage), submersible, jet pump; (b) Positive displacement — reciprocating, hand pump; (c) Special — airlift, hydraulic ram, solar pump. Write a one-line description for each. Section 8.2.

CHAPTER SUMMARY AND EXAM KEY POINTS

EXAM FORMULA SHEET — CHAPTER 8

Item Formula / Key Fact Context
Total dynamic head \( \text{TDH} = h_s + h_d + h_f + v^2/2g \) Sum of all heads the pump must overcome
Water power \( P_w = \gamma Q \cdot \text{TDH} / 1000 \) (kW) Power needed to lift water (100% efficiency)
Brake power \( P_b = P_w / \eta_p \) Actual shaft power accounting for pump losses
Motor power \( P_m = P_b / \eta_m \) Electrical input accounting for motor losses
Suction lift limit ≤ 6–7 m (centrifugal pump) Limited by atmospheric pressure minus vapour pressure
Centrifugal pump principle Priming → centrifugal force → volute (KE → PE) Most asked concept in this chapter
Submersible pump Motor + pump submerged; no priming; any depth Most used for deep tube wells
Deep-well turbine pump Bowl assembly submerged; motor at surface; 75–90% efficiency Irrigation, municipal high-discharge wells
Jet pump types Single-pipe (≤ 25 ft shallow) vs Double-pipe (25–110 ft deep) Low efficiency (25–40%); all moving parts at surface
Pump selection — Q Q ≤ safe yield of well Exceeding safe yield → excessive drawdown, aquifer depletion
Gravel pack design ve Screen entrance velocity ≤ 3 cm/s Prevents sand pumping and incrustation

KEY TAKEAWAYS FOR EXAM

  1. Centrifugal pump working principle is the single most asked topic (appeared in 2072 Ashwin + 2072 Magh). Know the 6 steps and draw the sketch with volute, impeller, suction pipe, and foot valve.
  2. Types of pumps: Appeared 2071 + 2073. Name at least 6 types with one-line descriptions under classified headings.
  3. Pump selection factors: Appeared 2078 + 2073. Organize under headings: well type, Q & head, power, water quality, economics, serviceability.
  4. Submersible pump: Know that it needs no priming, works at any depth, motor is submerged. Key advantage over centrifugal surface pump.
  5. Deep-well vertical turbine pump: Motor at ground level, bowl assembly submerged. Highest efficiency (75–90%) among deep-well pumps. High initial cost, needs skilled installation. Used for irrigation and municipal supply.
  6. Jet pump: Operates on Venturi effect (Bernoulli’s principle). Two types: single-pipe (shallow ≤ 25 ft) and double-pipe (deep, 25–110 ft). All moving parts at surface. Low efficiency but suitable for abrasive/corrosive water.
  7. No numericals from this chapter. Focus entirely on theory, description, and diagrams.
  8. Exam allocation: Typically 4 marks (one question only). Time management — spend 10–12 minutes maximum.
Exam Strategy: Chapter 8 Decision Flowchart CHAPTER 8 QUESTION “Types of pumps?” Classification chart (Fig 8.1) 6+ types, 1 line each “Centrifugal principle?” 6 steps + labelled sketch Advantages & limitations (Sec 8.3, Fig 8.2) “Selection factors?” 6 headings, 1–2 pts each (Sec 8.9) Theory only — 4 marks — 10–12 min. Always include a diagram.
Figure 8.4: Exam strategy for answering Chapter 8 questions.