portable slurry pump used

Centrifugal vs Positive Displacement: Pros and Cons Guide

What is a Centrifugal Pump?

A centrifugal pump uses an impeller to move fluid by converting rotational energy into kinetic energy. As the impeller spins, it throws fluid outward, creating flow and pressure. These pumps are often found in systems that move water or other non-viscous fluids--like HVAC loops, irrigation systems, or light industrial processes.

Centrifugal pumps tend to work best when flow conditions remain fairly steady and when the fluid isn’t too viscous. They have fewer moving parts, which means they can be easier to maintain and less expensive upfront. However, their performance can drop off sharply if the fluid properties or system conditions change too much.

What is a Positive Displacement Pump?

A positive displacement pump moves fluid by trapping a fixed amount and forcing it through the system. This design delivers a constant flow, even if the system pressure varies. These pumps are common in applications involving thick fluids, metering needs, or environments where precise flow is required.

Positive displacement pumps handle high-viscosity fluids, shear-sensitive materials, and situations where consistency matters. They can run at lower speeds and still maintain output, making them good for high-pressure or low-flow applications.

Positive Displacement Pump vs. Centrifugal Pump

While both pump types move fluid from one place to another, they do it in ways that affect how they perform in a system. Choosing one over the other depends on what kind of job the pump needs to do.

Flow Behavior

Centrifugal pumps are pressure-dependent: their flow rate varies with changes in system pressure or head. As system resistance increases, flow decreases.

Positive displacement pumps deliver a nearly constant flow regardless of changes in system pressure, assuming the pump and drive system can handle the pressure.

Pressure Handling

Centrifugal pumps operate efficiently at their best efficiency point (BEP), which corresponds to a specific flow and head. They are well-suited for applications with moderate pressure requirements and steady flow conditions. For higher pressures, specialized centrifugal designs like multistage pumps can be used.

Positive displacement pumps work better when the system has high resistance or needs consistent pressure. They build pressure as needed to overcome system resistance and maintain a steady output.

Viscosity

Positive displacement pumps can move viscous liquids with less impact on performance.

Centrifugal pumps are best for low-viscosity fluids. For most commercial systems moving water or similar fluids, this works perfectly.Centrifugal pumps tend to lose efficiency as viscosity increases, typically performing best below ~100 cSt. This makes them ideal for systems handling water, glycol blends, and other low-viscosity fluids commonly found in HVAC, light industrial, and commercial applications.

Efficiency

At or near their design point, centrifugal pumps can be very efficient. Their simplicity and lower energy use make them a smart choice for steady applications. Centrifugal pumps perform at their best efficiency point (BEP), which is the flow and head condition where hydraulic losses are minimized. Operating close to BEP ensures longer pump life, reduced maintenance, and optimal energy usage.

Positive displacement pumps stay closer to their expected output across different conditions.

Suction Conditions

Centrifugal pumps need a good setup to avoid cavitation.When system design accounts for this, they offer reliable, consistent service. While positive displacement pumps can tolerate more suction variation, centrifugal pumps (when properly installed) offer excellent reliability and avoid cavitation issues through thoughtful NPSH design.

Cost and Maintenance

Centrifugal pumps usually cost less upfront and are simple to keep going. Positive displacement pumps cost more, and they’ve got more parts.

Choosing the Right Pump for Your Application

When selecting a pump, it helps to start by considering your fluid and your system:

• Is the fluid thin (non-viscous) or thick (viscous)?
• Does your system encounter high resistance?
• Is flow rate consistency important?
• Are you pumping a product that shouldn’t be agitated or sheared?

Centrifugal pumps are a good fit for water-like fluids, large flow rates, and systems with stable conditions. They cover a broad range of applications and are ideal for many of the systems we support at American Stainless Pumps.