A centrifugal pump uses a rotating impeller to add velocity to the fluid, then converts part of that velocity into pressure as it passes through the casing. A positive displacement pump traps a defined volume of fluid and moves it mechanically through the pump each cycle or revolution. That difference in operating principle explains most of the practical differences between them or how their flow responds to changing pressure, how they handle viscosity and solids, and how they fail.
How each pump responds to changing system pressure
A centrifugal pump’s flow changes as system resistance changes. If discharge pressure rises, flow falls along the pump curve, and it approaches zero flow as the system approaches shut-off head. This makes centrifugal pumps forgiving of a partially closed valve, but means the delivered flow is never fixed — it depends on the whole system.
A positive displacement pump’s flow is set mainly by displacement per cycle and speed, largely independent of discharge pressure, subject to internal slip. A blocked discharge does not reduce flow the way it does on a centrifugal pump — pressure rises rapidly instead, which is why positive displacement pumps require a properly sized relief path for the full pump flow.
Where each pump type tends to suit better
| Application condition | Centrifugal pump tendency | Positive displacement pump tendency |
|---|---|---|
| Clean, low-viscosity fluid at moderate or high flow | Often a strong candidate | May be suitable, but can add unnecessary complexity |
| High-viscosity fluid | Performance and efficiency may fall substantially | Often handles viscosity more predictably |
| Accurate low-flow dosing | Difficult to control accurately at standard designs | Metering designs are commonly used |
| Variable system pressure | Flow changes along the pump curve | Flow can remain comparatively stable, subject to slip |
| Large or abrasive solids | Requires a suitable slurry or solids-handling design | Suitability depends heavily on clearances and pumping principle |
| Shear-sensitive fluid | High-speed designs may damage some products | Some low-speed designs are gentler |
| Blocked discharge | Flow falls as shut-off is approached | Pressure can rise rapidly; sized relief is required |
Efficiency, NPSH and mechanical differences
Centrifugal pumps generally have fewer wearing parts in contact with the fluid and can run continuously at high speed with good efficiency at their Best Efficiency Point, but efficiency falls away from that point. Positive displacement pumps often maintain more consistent efficiency across a range of speeds, but have more wearing internal parts — gears, lobes, vanes, diaphragms or valves — that require periodic replacement.
NPSH requirements also differ. Centrifugal pumps have a published NPSH required curve that varies with flow. Positive displacement pumps typically need enough inlet pressure to fill the pumping chamber at the required speed, which becomes more critical with viscous fluids or high pump speeds.
Neither pump type is universally better
Choosing between a centrifugal and a positive displacement pump comes down to the fluid, the required flow accuracy, how the system pressure behaves and how the pump must handle solids or shear. A centrifugal pump is often the simpler, lower-maintenance choice for clean or moderately viscous fluids at moderate to high flow. A positive displacement pump is often the better choice for viscous fluids, precise dosing, or where flow needs to stay stable against a variable system pressure.
The technology family is only the starting point. See the pump selection guide to work through the full application data before comparing individual pump designs.
Centrifugal vs Positive Displacement Pumps FAQs
Which pump type is more efficient?
Neither is universally more efficient. A centrifugal pump can be highly efficient at its Best Efficiency Point but loses efficiency away from it. A positive displacement pump can hold efficiency across a wider speed range but has more wearing parts that affect long-term performance. Efficiency depends on the specific pump and duty, not the general category.
Can a centrifugal pump handle thick fluids at all?
Some can, within limits. Performance, efficiency and required power all shift as viscosity rises, and manufacturer correction data should be applied to the specific pump curve. Beyond a certain viscosity, a positive displacement pump usually becomes the more practical option.
What is the simplest way to shortlist between the two?
Start from the fluid and duty, not the pump. Confirm viscosity, solids, required flow accuracy and how system pressure varies, then check the table above against those confirmed conditions. Where the fluid or duty sits close to the limits of either technology, treat the shortlist as a starting point for further comparison rather than a final answer.
This article explains general tendencies. It does not replace a full application review or manufacturer-confirmed performance data for the specific pump and duty.
Part of the pump selection guide. See also How Viscosity Affects Pump Selection, How Solids Affect Pump Selection and Why Oversizing Pumps Causes Problems.
About The Pump Expert
The Pump Expert provides independent, practical education for pump users, engineers and maintenance teams. TPE explains how pumps and pump systems behave so readers can make better technical decisions without supplier bias.
Last Updated on July 30, 2026 by TPE