If you’ve ever compared pump models for a project, you’ve probably seen this question pop up:
Should I use a centrifugal pump or a positive displacement pump?
At first, it sounds like a simple “Type A vs Type B” comparison. But in real installations, this choice decides whether your system runs smoothly… or turns into a constant headache of noise, unstable flow, seal failures, clogged lines, and energy waste.
Here’s the honest truth:
– Centrifugal pumps are the go-to option for most water transfer and circulation jobs.
– Positive displacement (PD) pumps are the problem-solvers when pressure is high, flow must be precise, or the liquid is difficult.
This guide explains the difference in a practical way, without textbook fluff. We’ll cover how each pump type works, where each one wins, where each one fails, and how to choose correctly.
Quick definition: centrifugal pump vs positive displacement pump
What is a centrifugal pump?
A centrifugal pump moves liquid by spinning an impeller. The impeller adds velocity to the liquid, and the pump casing converts that velocity into pressure.
Key idea:
Centrifugal pumps are flow machines.
They are great when you need steady flow and the system resistance is predictable.
What is a positive displacement pump?
A positive displacement pump moves liquid by trapping a fixed volume and pushing it forward. This is done using pistons, diaphragms, gears, lobes, screws, or progressive cavity rotors.
Key idea:
Positive displacement pumps are volume machines.
They deliver nearly constant flow even when pressure changes.
How they behave differently (this is what matters)
Most pump selection mistakes happen because people only compare horsepower or “maximum pressure.” That’s not how pumps behave in real piping systems.
Centrifugal pump behavior: flow changes with pressure
In a centrifugal pump system:
– If system pressure increases (more head, more restriction), flow drops
– If system pressure decreases (less head), flow rises
– If you close a discharge valve, flow can drop close to zero
This is why centrifugal pump curves slope downward: higher flow → lower head.
Centrifugal pumps are forgiving in many water systems, but they are sensitive to operating far away from their best efficiency point (BEP).
Positive displacement pump behavior: pressure changes with resistance
A PD pump keeps pushing a fixed volume forward.
That means:
– If system resistance increases, pressure increases
– Flow stays nearly the same until the pump reaches its mechanical or motor limit
– If you close the discharge valve, the pump will still try to push liquid
Important:
A PD pump must have a relief valve or bypass protection. Otherwise, deadheading can damage the pump or the system quickly.
Centrifugal vs PD pumps: the simplest comparison table
| Característica | Bomba centrífuga | Positive Displacement Pump |
| Flow behavior | Flow changes with pressure | Flow stays nearly constant |
| Pressure capability | Moderate to high (depends on design) | High pressure is common |
| Best for | Clean water, circulation, transfer | Viscous fluids, dosing, precise flow |
| Closed discharge | Short time (usually) | Dangerous without relief valve |
| Priming | Often needs priming | Many types self-prime |
| Efficiency range | Best near BEP | Often stable across conditions |
| Mantenimiento | Usually simpler | Depends on type (can be higher) |
| Solids handling | Some types handle solids | Many PD types handle solids better |
| Pulsation | Smooth (typically) | Pulsation possible (depends on type) |
Types of centrifugal pumps (common in real projects)
Centrifugal pumps come in many designs, including:
– End suction pumps (most common for general water)
– Split case pumps (high flow, irrigation, waterworks)
– Multistage pumps (high head, booster, RO, boiler feed)
– Vertical inline pumps (HVAC and building systems)
– Submersible centrifugal pumps (wells, drainage)
If your liquid is mostly water-like and your goal is moving volume efficiently, centrifugal is usually the first place to start.
Types of positive displacement pumps (and what they’re used for)
PD pumps include several families:
1) Diaphragm pumps
– Great for chemical dosing and slurry transfer
– Often used for metering and chemical injection
2) Gear pumps
– Common for oils and fuels
– Not ideal for abrasive solids
3) Progressive cavity pumps
– Excellent for sludge, thick fluids, shear-sensitive liquids
– Popular in wastewater and industrial processes
4) Screw pumps
– Good for viscous fluids
– Smooth flow, low pulsation5) Piston / plunger pumps
– Extremely high pressure capability
– Used for cleaning systems, injection, pressure testing
Which pump is better for water?
For clean water transfer, circulation, irrigation, HVAC, and most industrial cooling systems:
Centrifugal pumps usually win because they are efficient, widely available, easier to maintain, and cost-effective.
However, water systems can still require PD pumps when:
– you need precise dosing (chemicals, fertilizers)
– you need stable flow regardless of pressure
– you have a very low flow / high pressure requirement
Centrifugal pump vs PD pump for viscous liquids
Viscosity changes everything.
Centrifugal pumps lose efficiency fast when the liquid becomes thick. The pump may still run, but performance drops and power consumption rises.
PD pumps handle viscosity better because they physically push the liquid forward.
If your liquid feels like oil, syrup, sludge, or thick chemical mixtures, PD pumps are usually the safer choice.
Pressure control: where PD pumps shine
If you’re running a system where pressure varies constantly—like long pipelines with changing valves, filtration systems that clog over time, or dosing lines with small diameters—a centrifugal pump may “wander” in flow output as pressure changes.
A PD pump holds flow stable, which makes control easier. That’s why PD pumps are common in chemical dosing, metering, high-pressure injection, and consistent feed applications.
Cavitation and suction: which one is easier?
Both pump types can cavitate, but centrifugal pumps are often more sensitive because they require stable suction pressure and dislike air in the suction line.
Many PD pumps can self-prime and handle air better, but they can still be damaged by dry running depending on type.
Real-world rule:
– Centrifugal pumps need good suction design
– PD pumps need good protection (relief valves, dry-run protection)
Energy cost: which one is more efficient?
A centrifugal pump can be extremely efficient—if it operates near BEP.
But if the system conditions vary and the pump runs far away from BEP, efficiency drops and energy cost increases.
PD pumps often maintain efficiency more consistently across changing pressures (depending on design and viscosity).
So the better question is not “Which is more efficient?” but:
Which pump type will run in its comfort zone in your system?
Common selection mistakes (and how to avoid them)
Mistake 1: Choosing a centrifugal pump for a metering job
If you need stable, accurate flow, a centrifugal pump is often the wrong tool.
Mistake 2: Installing a PD pump without a relief valve
This is dangerous. PD pumps will build pressure until something fails.
Mistake 3: Ignoring viscosity
Centrifugal pumps hate thick liquids. PD pumps often love them.
Mistake 4: Selecting only by horsepower
Horsepower alone tells you nothing unless you know the duty point (flow + head/pressure).
Quick selection guide (fast answers)
Choose a centrifugal pump when you need:
– medium to high flow
– clean water or low-viscosity liquid
– simple, stable systems
– good efficiency and low cost
Choose a positive displacement pump when you need:
– precise, constant flow
– high pressure at low flow
– thick, viscous, or shear-sensitive liquids
– reliable dosing and metering
Final takeaway
Centrifugal pumps and positive displacement pumps are both excellent technologies—but they solve different problems.
A centrifugal pump is usually the best choice for water transfer and circulation where the system is stable and efficiency matters.
A positive displacement pump is the better choice when you need accurate flow, high pressure, viscosity handling, or process control.
If you’re not sure which type fits your application, define your duty point clearly:
– required flow rate
– required head / pressure
– fluid properties (viscosity, solids)
– suction conditions
– operating pattern (continuous or intermittent)
Once those are clear, the “centrifugal vs PD” decision becomes obvious.