Centrifugal vs Positive Displacement Pump: Differences, Uses & How to Choose

How Each Pump Type Works

Centrifugal pumps and positive displacement pumps move fluid by entirely different mechanisms — and that single distinction drives nearly every performance difference between them. Understanding the working principle of each is the starting point for any informed pump selection.

A centrifugal pump converts rotational energy from a motor into kinetic energy in the fluid. As the impeller spins, it accelerates liquid outward from its center through centrifugal force, which is then converted into pressure at the discharge outlet. The faster the impeller spins, the more velocity is imparted to the fluid — but the relationship between flow and pressure is not fixed. Flow rate decreases as system back-pressure rises. For a detailed breakdown of centrifugal pump principles and design, including impeller geometry and casing configurations, the underlying engineering is worth examining closely before specifying one for a process.

A positive displacement (PD) pump works on an entirely different principle: it traps a fixed volume of fluid in a cavity — whether via gears, a diaphragm, a piston, rotary lobes, or a progressive cavity — and then physically forces that volume into the discharge line with each cycle or rotation. The amount of fluid delivered per revolution or stroke stays essentially constant, regardless of what the downstream pressure is doing. That mechanical certainty is the defining characteristic of the PD pump, and it is both its greatest strength and, in certain situations, its limitation.

Performance Curves: The Key Difference Engineers Care About

Plot the performance curves of these two pump types side by side and the contrast becomes immediate. On a centrifugal pump curve, flow rate and pressure head have an inverse relationship: as back-pressure increases, flow drops. The pump operates most efficiently at a specific point — the Best Efficiency Point (BEP) — and performance degrades on either side of it. Engineers must design systems so that the operating point stays close to the BEP; running a centrifugal pump far off-curve leads to energy waste, vibration, and premature wear.

A positive displacement pump's curve looks almost nothing like this. Because it moves a fixed volume per cycle, flow rate remains nearly constant across a wide range of discharge pressures. As pressure rises, flow barely changes. This makes PD pumps inherently suitable for dosing, metering, and any application requiring a predictable, consistent output. The tradeoff is that if the discharge line is blocked, pressure will continue to build until something fails — which is why most positive displacement pump installations require a pressure relief valve.

Understanding how flow rate and head interact in a given system is essential before committing to either pump type. A full treatment of understanding pump flow rate and head helps clarify how these parameters interact with pipe length, friction losses, and system resistance in real installations.

Handling Viscosity: Where Each Pump Wins or Struggles

Fluid viscosity is arguably the single most important variable when choosing between a centrifugal and a positive displacement pump. The two types respond to viscosity in opposite ways — which means choosing the wrong one can result in severe efficiency losses or outright pump failure.

Centrifugal pumps perform best with low-viscosity fluids: water, light chemicals, thin solvents, and similar liquids that flow freely. As viscosity rises, frictional losses inside the pump increase rapidly. Flow rate drops, head decreases, efficiency falls, and power consumption climbs. Above roughly 200–400 centipoise (depending on pump design), the performance degradation of a centrifugal pump becomes severe enough to make it an impractical choice.

Positive displacement pumps respond to increasing viscosity very differently. As the fluid gets thicker, a PD pump often becomes more efficient, not less — because higher viscosity reduces internal leakage through clearances. Gear pumps, lobe pumps, and progressive cavity pumps are routinely used to transfer oils, adhesives, slurries, polymers, and other high-viscosity media that would stall a centrifugal pump entirely. PD pumps also handle shear-sensitive fluids more gently, because they generate lower internal velocities — a critical advantage in food processing, pharmaceuticals, and biological applications where the fluid must not be degraded by mechanical forces.

Head-to-Head Comparison

The table below summarizes the most operationally significant differences between the two pump categories across the parameters that matter most in industrial and chemical process environments.

Common Applications for Each Pump Type

The application profiles of centrifugal and positive displacement pumps reflect their respective strengths. Knowing where each type dominates helps engineers narrow down options before detailed engineering begins.

Centrifugal pumps are the workhorses of municipal water supply, HVAC circulation, cooling systems, and large-volume liquid transfer. In the chemical industry, they handle acids, alkalis, solvents, and process water where viscosity is low and high throughput is the priority. They are also the standard choice in wastewater treatment, fire suppression, and agricultural irrigation — applications where consistent high flow rates at moderate pressures are required. For an overview of different types of centrifugal pumps and their industrial uses, including radial flow, axial flow, and magnetic drive variants, there is a wide spectrum of configurations suited to different process demands.

Positive displacement pumps come into their own where centrifugal pumps fall short. Gear pumps and lobe pumps are standard in lubricating oil systems, hydraulics, and food-grade applications involving syrups, sauces, and edible oils. Diaphragm pumps and peristaltic pumps serve chemical dosing and pharmaceutical manufacturing, where precise metering and contamination prevention are non-negotiable. Progressive cavity pumps handle thick slurries and abrasive media in mining, wastewater, and drilling operations. Piston and plunger pumps deliver the very high pressures demanded in descaling, hydrostatic testing, and high-pressure cleaning systems.

How to Choose the Right Pump for Your Process

Selecting between a centrifugal and a positive displacement pump comes down to four questions asked in sequence. Answer them honestly against your actual process conditions — not idealized design conditions — and the correct pump type usually becomes clear.

1. What is the fluid viscosity? If it is consistently below 200 cP, a centrifugal pump is the natural starting point. If it is above 500 cP, or if viscosity varies significantly across operating conditions, a positive displacement pump will deliver more predictable performance.
2. What does the flow profile need to look like? If precise, metered, or constant flow is required — regardless of what happens to downstream pressure — a PD pump is the correct choice. If the application tolerates variable flow and the priority is high throughput, a centrifugal pump is more efficient and cost-effective.
3. What pressure does the system demand? For very high discharge pressures — above what a single-stage centrifugal pump can deliver — PD pumps offer a more direct path to the required output. For moderate pressures with high flow, centrifugal (including multistage) designs are typically the better fit.
4. What are the fluid's special characteristics? Shear sensitivity, abrasiveness, solid content, and chemical aggressiveness all influence both pump type and materials selection. For corrosive process fluids in particular, the guide to choosing the right pump for corrosive fluids walks through material compatibility for common aggressive chemicals including acids and solvents.

For applications involving hazardous or high-value process fluids where leakage cannot be tolerated, chemical magnetic pumps for leak-free fluid transfer offer a specialized solution that eliminates mechanical seals entirely — relevant to both centrifugal and certain PD configurations. The U.S. Department of Energy's official guidance on pump selection considerations provides a rigorous framework for evaluating system requirements, fluid properties, and energy efficiency factors in industrial pump specification. For a comprehensive look at available pump configurations across both categories, the full range of industrial chemical pumps covers centrifugal, magnetic drive, and specialty options engineered for demanding chemical process environments.