Centrifugal Pumps: How They Work, Types, Specifications & Selection Guide
Centrifugal pumps handle approximately 70% of all industrial pumping worldwide. From a small 0.5 kW booster pump in a building to a 5,000 kW split-case unit feeding a municipal water network — if the fluid is clean and the viscosity is low, a centrifugal pump is almost certainly the right choice.
They dominate because they are simple, efficient, reliable, and available in an enormous range of sizes and materials. But "centrifugal pump" covers dozens of configurations — end suction, split case, multistage, vertical turbine, inline, self-priming — and choosing the wrong type wastes energy, increases maintenance, and shortens pump life.
This guide explains how centrifugal pumps work, covers every major type, breaks down the performance parameters you need to understand, and gives you a clear framework for selecting the right pump for your application.
How a Centrifugal Pump Works
The operating principle is straightforward: a motor spins an impeller inside a casing. The spinning impeller accelerates the fluid outward by centrifugal force, converting mechanical energy (rotation) into kinetic energy (fluid velocity). The casing then converts that velocity into pressure energy as the fluid slows down and exits through the discharge nozzle.
The process step by step:
Fluid enters the pump through the suction nozzle and reaches the center (eye) of the impeller
The impeller vanes accelerate the fluid radially outward as the impeller rotates
The fluid exits the impeller at high velocity and enters the volute casing (a spiral-shaped chamber that gradually increases in cross-section)
As the fluid moves through the expanding volute, velocity decreases and pressure increases
The pressurized fluid exits through the discharge nozzle at the required pressure
Key point: A centrifugal pump does not "suck" fluid — it can only add energy to fluid that is already present at the impeller eye. This is why suction conditions (NPSH) are so critical and why centrifugal pumps must be primed before starting (unless they are self-priming or submersible designs).
Types of Centrifugal Pumps
End Suction Pumps
The most common centrifugal pump configuration. Fluid enters axially through the suction nozzle on one end and exits radially through the discharge nozzle on top or side of the casing. A single impeller is mounted on an overhung shaft supported by bearings on one side.
Characteristics:
Simplest design, lowest cost, smallest footprint
Single-stage (one impeller), suitable for heads up to approximately 120 meters
Flow rates typically from 1 to 500 m³/h
Available in close-coupled (motor directly mounted on pump) and long-coupled (motor connected via coupling and baseplate) configurations
Close-coupled versions are the most compact and economical for smaller applications
Best for: General water transfer, HVAC circulation, irrigation, light industrial process, cooling water, and any application requiring moderate flow and head with clean fluids.
Limitations: Single suction impeller creates axial thrust that must be managed by bearings. Not ideal for very high flow rates (above ~500 m³/h) or high heads (above ~120m). Maintenance requires disconnecting piping or removing the pump from the baseplate (unless back-pullout design is used).
Split Case Pumps (Horizontal Split)
The pump casing splits horizontally into upper and lower halves. The impeller is a double-suction design — fluid enters from both sides simultaneously, which balances axial thrust and allows much higher flow rates than single-suction end-suction pumps.
Characteristics:
Double-suction impeller provides balanced hydraulic forces, longer bearing life, and lower vibration
Very high flow rates — from 100 to 10,000+ m³/h
Heads up to approximately 200 meters (single stage) or higher with multi-stage
Peak efficiency often exceeds 85% — the most energy-efficient centrifugal pump type
Horizontal split allows complete access to internals (impeller, wear rings, seals) without disconnecting piping — maintenance is significantly faster and cheaper
Best for: Municipal water supply pumping stations, power plant cooling water, large irrigation schemes, fire protection systems, industrial cooling water circuits, and any high-flow application where efficiency and reliability are critical.
Why it matters for Africa and Middle East: Split-case pumps are the standard for municipal water treatment plant raw water intake and treated water distribution. Any water supply project serving a town or city will likely specify split-case pumps for the main pumping station.
Multistage Pumps
Multiple impellers are mounted on a single shaft, arranged in series. Each impeller (stage) adds pressure to the fluid. The discharge of one stage feeds directly into the suction of the next. The result is very high discharge pressure from a relatively compact pump.
Characteristics:
2 to 15+ stages, generating heads from 100 to 600+ meters
Flow rates typically from 1 to 200 m³/h (horizontal multistage) or up to 500+ m³/h (vertical multistage)
Available in horizontal and vertical configurations
Horizontal multistage pumps are used for high-pressure process applications
Vertical multistage (inline) pumps mount directly in the pipeline, saving floor space
Best for: Boiler feedwater (power plants), reverse osmosis desalination feed, high-pressure cleaning, pipeline pressure boosting, high-rise building water supply, and fire-fighting booster systems.
Vertical Turbine Pumps
The pump bowls (impellers and diffusers) are submerged in the water source — a well, sump, river intake, or reservoir. A long vertical shaft connects the submerged pump bowls to a motor mounted above ground. Multi-stage designs generate the head needed to lift water from deep sources.
Characteristics:
Pump bowls submerged, motor above ground — no suction lift limitations
Multi-stage designs for heads up to 300+ meters
Flow rates from 10 to 5,000+ m³/h
Column pipe lengths up to 30+ meters (for deep sumps/intakes)
Can be driven by electric motor (top-mounted), diesel engine (right-angle gear drive), or submersible motor (wet-pit submersible configuration)
Best for: Municipal water supply from surface water intakes (rivers, lakes, reservoirs), deep sump pumping, cooling water intake structures, irrigation from canals and rivers, and dewatering applications where the pump must draw from a deep wet well.
Difference from submersible borehole pumps: Vertical turbine pumps have the motor above ground and are used in open sumps, intakes, and large-diameter wells. Submersible borehole pumps have the motor submerged and are designed for narrow drilled boreholes. Both are centrifugal pumps — the difference is the motor location and installation environment.
Self-Priming Pumps
Standard centrifugal pumps cannot evacuate air from the suction line — they must be primed (filled with fluid) before starting. Self-priming pumps have a recirculation chamber in the casing that retains fluid after the pump stops. When restarted, this retained fluid mixes with incoming air, creating a liquid-air mixture that is separated in the recirculation chamber, gradually evacuating the air and establishing full prime.
Characteristics:
Can lift fluid from below the pump without external priming assistance
Suction lift up to approximately 7–8 meters (limited by atmospheric pressure)
Slightly lower efficiency than non-self-priming designs due to the recirculation chamber
Available in clean water and solids-handling (trash pump) configurations
Best for: Construction site dewatering, agricultural irrigation from ponds or rivers, tank emptying, portable pumping applications, and any installation where the pump is above the fluid source and priming is impractical.
Inline Pumps
The suction and discharge nozzles are on the same centerline (inline), allowing the pump to be installed directly in the pipeline without a separate foundation. The motor mounts vertically on top. Compact footprint makes inline pumps ideal for mechanical rooms and tight spaces.
Best for: HVAC circulation, building pressure boosting, and industrial process applications where floor space is limited.
Key Performance Parameters
Understanding these parameters is essential for selecting and specifying a centrifugal pump:
Flow Rate (Q)
The volume of fluid the pump delivers per unit time, measured in m³/h (cubic meters per hour), l/s (liters per second), or GPM (US gallons per minute).
Conversion: 1 m³/h = 0.278 l/s = 4.40 GPM
The required flow rate is determined by the process demand — how much fluid must be moved to meet the system's needs. Oversizing the flow rate wastes energy; undersizing fails to meet demand.
Total Dynamic Head (TDH)
The total pressure the pump must develop, measured in meters of fluid column. TDH is the sum of:
Static head — the vertical height difference between the fluid source and the delivery point
Friction head — the pressure lost due to friction in the piping system (depends on pipe size, length, material, fittings, and flow velocity)
Pressure head — any pressure required at the delivery point (e.g., 3 bar at a distribution network = 30.6 meters)
TDH = Static head + Friction head + Pressure head
NPSH (Net Positive Suction Head)
The most misunderstood — and most critical — parameter in centrifugal pump selection.
NPSHr (Required) — the minimum suction pressure the pump needs at the impeller eye to avoid cavitation. This value is published by the pump manufacturer and varies with flow rate.
NPSHa (Available) — the actual suction pressure available from the system, determined by: atmospheric pressure minus the vertical suction lift minus the friction losses in the suction piping minus the vapor pressure of the fluid at the operating temperature.
The rule: NPSHa must always exceed NPSHr. If the available suction pressure drops below what the pump requires, the fluid begins to vaporize at the impeller eye — forming and collapsing vapor bubbles (cavitation). Cavitation destroys impellers within weeks, creates noise and vibration, and dramatically reduces pump performance.
Practical implication: At high altitudes (lower atmospheric pressure) and with hot fluids (higher vapor pressure), NPSHa decreases. Projects at altitude in Africa (Nairobi is at 1,795m, Addis Ababa at 2,355m) must account for reduced atmospheric pressure when calculating NPSHa.
Efficiency
The ratio of hydraulic power output (flow × head) to the mechanical power input (motor shaft power). Expressed as a percentage.
Peak efficiency for centrifugal pumps ranges from 60% (small end-suction) to 88%+ (large split-case). Pumps are most efficient at their Best Efficiency Point (BEP) — the flow rate where the pump design is optimized. Operating far from BEP (either at low flow or high flow) reduces efficiency, increases vibration, and shortens pump life.
Always select a pump where the required operating point is within 80–110% of BEP flow. This ensures efficient, reliable, and long-life operation.
Materials of Construction
Material | Application |
|---|---|
Cast iron (GG25/GGG40) | Standard for clean water, HVAC, general service. Lowest cost. |
Ductile iron (GGG50) | Higher strength than grey cast iron. Used for high-pressure and larger pumps. |
Bronze-fitted (CI body, bronze impeller/wear rings) | Seawater, brackish water, and applications requiring corrosion resistance at the wetted parts. Standard for marine and coastal. |
All bronze / gunmetal | Marine, seawater, and corrosive service for smaller pumps. |
Stainless steel 304 | Mildly corrosive fluids, food and beverage, pharmaceutical. |
Stainless steel 316 | Chloride-containing fluids, chemical processing, aggressive water chemistry. |
Duplex stainless steel | High-strength corrosion resistance, offshore, desalination. |
High-chrome iron (A532) | Abrasive slurry service, mining, dredging. |
Rubber-lined | Highly abrasive slurries with large particles. |
For most water supply projects in Africa and the Middle East: Cast iron body with bronze-fitted internals is the standard specification. It provides good corrosion resistance at moderate cost. For coastal installations or brackish water, full bronze or stainless steel 316 may be required.
Mechanical Seals vs Gland Packing
The shaft seal prevents fluid leaking out where the shaft passes through the casing.
Mechanical seal — two precision-lapped faces (one rotating, one stationary) running against each other with a thin fluid film between them. Virtually drip-free. Standard for most industrial and municipal applications. Materials: carbon/silicon carbide or carbon/ceramic faces, with elastomer secondary seals (NBR, Viton, EPDM).
Gland packing — braided rings of flexible material compressed around the shaft by a packing gland. Allows a controlled drip (necessary for lubrication and cooling). Lower cost, easier to adjust in the field, but requires periodic tightening and replacement. Still common in some water utility applications.
For new installations, always specify mechanical seals unless the project specifically requires gland packing (e.g., for abrasive slurry where seal faces would be quickly destroyed).
How to Select a Centrifugal Pump
Step 1 — Define the duty point. Flow rate (Q) and total dynamic head (TDH) at the required operating conditions. This is the single point on the pump performance curve where the pump must operate.
Step 2 — Calculate NPSHa. Based on suction conditions, altitude, and fluid temperature. Ensure the selected pump's NPSHr is at least 1–2 meters below NPSHa.
Step 3 — Choose the pump type. Based on flow, head, and application:
Flow Range | Head Range | Recommended Type |
|---|---|---|
1–500 m³/h | Up to 120m | End suction |
100–10,000+ m³/h | Up to 200m | Split case |
1–200 m³/h | 100–600+ m | Multistage |
10–5,000+ m³/h | Up to 300m (from sump) | Vertical turbine |
1–200 m³/h | Up to 80m (suction lift needed) | Self-priming |
Step 4 — Select the operating point near BEP. The duty point should fall between 80% and 110% of the pump's BEP flow. Ask the pump supplier for the performance curve and verify.
Step 5 — Choose materials. Based on fluid chemistry, temperature, and abrasiveness.
Step 6 — Specify the motor. Voltage (380V/415V for most Africa and ME), frequency (50Hz), protection class (IP55 minimum), insulation class (F), and hazardous area classification if required (ATEX/IECEx).
Step 7 — Select the seal. Mechanical seal for most applications. Specify seal face materials and elastomers based on fluid compatibility.
Which Centrifugal Pump for Which Application?
Application | Pump Type | Typical Size Range |
|---|---|---|
Building water supply / pressure boosting | End suction or vertical multistage | 2–50 m³/h, 30–80m head |
HVAC circulation | End suction or inline | 5–200 m³/h, 10–40m head |
Municipal water supply (pumping station) | Split case | 100–5,000 m³/h, 30–100m head |
Irrigation (from river/canal) | End suction, split case, or vertical turbine | 20–2,000 m³/h, 10–80m head |
Boiler feedwater (power plant) | Horizontal multistage | 10–200 m³/h, 200–500m head |
Fire protection (NFPA 20) | Split case or end suction (UL/FM rated) | 50–500 m³/h, 40–120m head |
Desalination RO feed | Horizontal multistage | 10–100 m³/h, 300–600m head |
Cooling water (power plant) | Split case or vertical turbine | 500–10,000 m³/h, 20–60m head |
Construction dewatering | Self-priming | 10–200 m³/h, 10–30m head |
Process water transfer | End suction | 5–300 m³/h, 20–80m head |
Seawater intake | Vertical turbine (bronze-fitted) | 100–5,000 m³/h, 10–40m head |
High-rise building supply | Vertical multistage | 5–100 m³/h, 80–200m head |
Supply from Kasko Makine
Kasko Makine supplies the complete range of centrifugal pumps for water, process, and industrial applications:
End suction pumps: Close-coupled and long-coupled. Cast iron, bronze-fitted, stainless steel. 0.37 kW to 315 kW. Flow rates 1–500 m³/h.
Split case pumps: Horizontal split, double suction. Cast iron and bronze-fitted. Flow rates 100–10,000+ m³/h. For municipal water supply, fire protection, and cooling water.
Multistage pumps: Horizontal and vertical. 2–15 stages. For boiler feedwater, RO desalination, pressure boosting. Heads up to 600+ meters.
Vertical turbine pumps: For deep sumps, river intakes, and reservoir pumping. Multi-stage, long column. Electric and diesel drive options.
Self-priming pumps: Clean water and trash pump configurations. For construction, irrigation, and portable applications.
Complete pump packages: Pump + motor + baseplate + coupling + control panel + suction and discharge piping. Engineered and shipped ready for installation.
We also supply the HDPE pipe, steel pipe, flanges, fittings, and valves that connect to your pump station — single-source procurement for your complete water or process system.
All pumps supplied with certified performance curves, GA drawings, motor data sheets, and operation/maintenance manuals. Third-party inspection and factory witness testing available on request.
FAQ SCHEMA
Q: How does a centrifugal pump work?
A: A centrifugal pump uses a rotating impeller to accelerate fluid outward by centrifugal force. Fluid enters at the center (eye) of the impeller, is accelerated radially, and exits into a spiral volute casing that converts the velocity into pressure. The pressurized fluid then exits through the discharge nozzle. The pump adds energy to fluid — it does not "suck" fluid, which is why proper suction conditions (NPSH) are critical.
Q: What is the difference between end suction and split case pumps?
A: End suction pumps have a single suction impeller, are compact and lower cost, and handle flows up to about 500 m³/h. Split case pumps have a double suction impeller, handle much higher flows (up to 10,000+ m³/h), are more efficient (85%+), and allow maintenance without disconnecting piping. Split case pumps are standard for municipal water supply and large industrial applications.
Q: What is NPSH and why does it matter?
A: NPSH (Net Positive Suction Head) is the suction pressure available at the pump impeller. If NPSHa (available from the system) drops below NPSHr (required by the pump), cavitation occurs — vapor bubbles form and collapse inside the pump, destroying the impeller within weeks. Always ensure NPSHa exceeds NPSHr by at least 1–2 meters. High altitude and hot fluids reduce NPSHa.
Q: What type of centrifugal pump is used for boiler feedwater?
A: Multistage centrifugal pumps are standard for boiler feedwater because they generate the high pressures needed (200–500+ meters of head) to push water into a pressurized boiler. They use multiple impellers in series on a single shaft, with each stage adding pressure.
Q: What is the best efficiency point (BEP) and why does it matter?
A: BEP is the flow rate at which the pump operates at its highest efficiency. Operating significantly below or above BEP reduces efficiency, increases vibration, causes bearing and seal damage, and shortens pump life. Always select a pump so that the required operating point falls between 80% and 110% of BEP flow.
Q: What material should a centrifugal pump be made from?
A: Cast iron for clean water and general service (lowest cost). Bronze-fitted (CI body with bronze impeller and wear rings) for seawater, brackish water, and coastal installations. Stainless steel 316 for chemical processing and aggressive water chemistry. High-chrome iron for abrasive slurry service. Always match the pump materials to the fluid chemistry and temperature.
Request a centrifugal pump quotation — send us your flow rate (m³/h), total dynamic head (m), fluid type, and application to info@kaskomakine.com or WhatsApp +90 (537) 521 1399 . We respond within 24 hours and deliver to projects across Africa, the Middle East, Central Asia, and beyond.