Centrifugal Pumps vs. Positive Displacement Pumps

When it comes to selecting the right pump for your business, understanding the differences between positive displacement pumps and centrifugal pumps is imperative. Both types of pumps indeed serve essential functions in various industries. However, they operate differently and are suited to distinct applications. Industrial pumps come in two primary categories: centrifugal pumps and positive displacement pumps. Each type has unique properties concerning efficiency, flow rate, viscosity, and pressure.

In this comprehensive guide, we will take the time to compare positive displacement pumps to centrifugal pumps, explore their specific types, review how each mechanism works, examine a detailed comparison table, and help you determine which option is the right choice for your business operations.

Selecting The Right Pump For Your Business? Message Our Experts

What Are Positive Displacement Pumps?

Positive displacement pumps are engineered to move fluid by trapping a fixed amount of liquid and pushing that trapped volume directly into a discharge pipe. The internal structure prevents backflow and ensures that fluid will not circulate back toward the pump’s inlet. They have a well-earned reputation for effectively delivering a consistent flow rate regardless of changes in pressure, making them ideal for applications where precise fluid control is necessary.

Advantages of Positive Displacement Pumps

Accurate & Predictable Flow: Because the internal chambers hold a fixed volume, flow depends directly on pump speed. This allows for highly accurate calculations regarding pump flow and output per revolution.
Consistent Pressure: These pumps generally deliver constant pressure at levels higher than standard system requirements, which is vital in applications with varying discharge pressures (such as spray operations, dosing, or tanker loading).
Viscosity Versatility: Viscosity does not hinder these designs. In fact, positive displacement pumps become more efficient as fluid viscosity increases, operating exceptionally well with thick, heavy liquids.
Low Wear & Tear: Positive displacement pumps offer greater speed regulation than centrifugal pumps. Running at lower speeds enables better handling of solid- or abrasive-laden materials, minimizing overall wear.
Liquid Characteristic Preservation: When handling sensitive materials like gels, polymers, creams, or milk, preserving liquid structure is critical. Low internal velocity generates minimal shear force, making these pumps gentle on shear-sensitive products.

Types of Positive Displacement Pumps

Positive displacement pumps fall into two main categories—reciprocating and rotary pumps—alongside traditional linear designs:

1. Positive Displacement Reciprocating Pumps

Reciprocating pumps use an oscillating back-and-forth motion to move fluid:

Diaphragm Pump: Uses a flexible elastomer cover to displace fluid. Liquid is drawn in and expelled as the diaphragm expands and contracts. Because wet and dry chambers remain completely separate without dynamic seals, diaphragm valves and pumps are frequently used for toxic, hazardous, or corrosive liquids.
Piston Pump: Features a reciprocating piston moving within a cylinder alongside check valves on both ends. As the chamber expands, pressure drops and allows fluid to enter the intake.
Plunger Pump: Works similarly to a piston pump but utilizes a high-pressure plunger mechanism. They are commonly used where controlled, high-pressure flow generation is required, such as in oil and gas production, pressure washing, and hydrostatic testing.

2. Positive Displacement Rotary Pumps

Rotary pumps rely on rotating components to trap and move fluid within the pump casing:

Gear Pump: Uses two intermeshing gears. Fluid gets trapped between the gear teeth and the internal housing wall before being pushed toward the outlet.
Screw Pump: Features one or several threaded shafts that resemble screws. Spinning at low RPMs within the housing, these shafts trap liquid and move it smoothly along the length of the housing toward the discharge port.
Vane Pump: Utilizes sliding vanes mounted in an eccentric rotor. As the rotor spins, the vanes slide outward against the casing, capturing pockets of fluid and moving them forward.
Peristaltic Pump: Traps fluid inside a flexible hose or tube, which is compressed by rotating rollers. The squeezing action forces fluid toward the pump’s outlet. They are widely used in food and beverage, chemical processing, and biotechnology.
Lobe Pump: Contains two driven, non-contacting rotors with rounded lobes. They offer low shear and are simple to clean and sterilize, making them ideal for hygienic pharmaceutical and food processing plants.
Progressive Cavity Pump: Specially suited for challenging applications, moving highly viscous fluids or materials containing dense solids, such as dirt, grit, or sludge.

3. Linear Positive Displacement Pumps

Traditional mechanisms, such as rope pumps and chain pumps, have been used globally for centuries to draw up water through physical displacement.

Positive Displacement Pump Applications

Because of their ability to maintain steady flow rates and handle thick liquids under high pressure, positive displacement pumps are frequently found in:

Chemical Processing: Precise chemical dosing and viscous fluid handling.
Oil Processing Centers: Transferring crude oil, heavy sludge, and abrasive slurries.
Food and Beverage Production: Handling sensitive ingredients like creams, syrups, oils, and milk without breakdown.
Municipal Sewage Systems: Moving thick, solids-laden wastewater.
Pharmaceutical Plants: Safely transferring sterile, high-value liquid compounds.

What Are Centrifugal Pumps?

Centrifugal pumps are dynamic machines designed to move liquids by converting rotational energy, supplied by an electric motor or engine, into hydrodynamic energy. Rather than trapping fixed amounts of fluid, centrifugal pumps impart velocity directly to the fluid via a spinning element, pushing it through the casing and out into the piping network.

What Are the Benefits of Centrifugal Pumps?

Centrifugal pumps are among the most widely used industrial pumps due to several clear advantages:

Simplistic Design: Their straightforward mechanical construction makes them an economical and affordable option.
Fewer Moving Parts: A simpler internal design translates directly to fewer components that can wear out or require routine maintenance over the equipment’s lifespan.
Various Shapes and Sizes: Manufactured in a variety of sizes, they fit easily into diverse spaces and tight operational layouts.
High-Volume Efficiency: They provide exceptional energy efficiency when moving large volumes of low-viscosity fluids continuously.

Types of Centrifugal Pumps

Single-Stage Centrifugal Pumps: Built with a single impeller, making them suitable for high-flow, low-to-medium pressure tasks.
Multi-Stage Centrifugal Pumps: Equipped with multiple impellers arranged in series to build progressively higher pressures.
Submersible Pumps: Hermetically sealed units designed to operate entirely underwater or within the fluid being pumped, such as in sumps, wells, and drainage pits.

Centrifugal Pump Applications

Centrifugal pumps are the preferred choice across industries where high volumes of thin fluid must be moved rapidly and continuously:

Municipal Water Systems & Water Treatment: Moving vast quantities of clean or treated water across city infrastructure.
HVAC Systems & Water Circulators: Circulating water and thermal fluids through industrial heating and cooling loops.
Agriculture & Irrigation: Distributing water across large agricultural fields and crop systems.
Firefighting Operations: Delivering high-volume water supply rapidly under urgent conditions.
Boiler Feeds & Cooling Towers: Handling light fuels, condensate, and cooling water.

How Each Pump Works: Operational Mechanics

While both types move fluid from one point to another, understanding their fundamental mechanical principles makes it easy to see why they behave differently in field operations.

How a Centrifugal Pump Works (Dynamic Velocity)

Centrifugal pumps rely on dynamic energy transfer to build liquid velocity:

Fluid Entry: Fluid enters through the suction port and enters the center (eye) of the rotating impeller.
Impeller Acceleration: As the motor spins the impeller at high speed, the rotating blades push the fluid outward toward the edges of the pump casing using centrifugal force.
Pressure Conversion: As the liquid leaves the impeller blades at high speed, it enters the expanding spiral volute (or diffuser casing). This expansion slows the fluid down, converting its kinetic velocity into hydrodynamic pressure that propels the fluid out the discharge pipe.

Operational Rule: Centrifugal pumps create pressure, which results in flow.

How a Positive Displacement Pump Works (Volumetric Displacement)

Positive displacement pumps rely on expanding and contracting mechanical volumes:

Cavity Expansion: As internal components (pistons, gears, lobes, or diaphragms) rotate or stroke back and forth, they create an expanding space on the suction side, generating a vacuum.
Fluid Capture: External pressure forces liquid into this expanded chamber. Once full, the internal components seal off the cavity, trapping a precise, fixed volume of fluid.
Physical Discharge: Continued mechanical motion contracts or sweeps through the chamber, physically forcing the trapped fluid out through the discharge port and into the pipeline.

Operational Rule: Positive displacement pumps create flow, which results in pressure.

Positive Displacement Pumps vs. Centrifugal Pumps

To evaluate how these two pump families perform head-to-head across key operational metrics, review the comparison below:

Performance Metric	Positive Displacement (PD) Pumps	Centrifugal Pumps
Operating Principle	Traps fixed volumes to force fluid forward (Flow results in pressure).	Imparts kinetic energy to build fluid velocity (Pressure results in flow).
Flow vs. Pressure Relationship	Delivers a consistent flow rate regardless of system pressure changes.	Flow rate varies directly with pressure; higher pressure reduces output flow.
Viscosity Capabilities	Highly effective with viscous materials; efficiency rises as fluid thickens.	Less effective as viscosity grows; internal friction losses drop efficiency above 850 cSt.
Self-Priming & Gas Handling	Creates negative inlet pressure, making them self-priming and capable of handling gases.	Requires liquid inside the casing to operate; cannot self-prime standard units or handle gas over 15% GVF.
Shearing Force	Low internal fluid velocities produce minimal shear, preserving sensitive liquids.	High rotational motor speeds create elevated shear rates within the fluid.
Maintenance Profile	More internal moving parts requiring scheduled care; highly durable against thick media.	Simple construction with fewer moving parts leads to lower overall maintenance requirements.
Ideal Application Fit	Low flow, high pressure, thick liquids, precise metering, and high suction lift tasks.	High flow, low-to-medium pressure, thin liquids, and continuous high-volume transfer.

How Do Positive Displacement Pumps and Centrifugal Pumps Differ?

Understanding the operational differences between positive displacement and centrifugal pumps is vital for selecting equipment that meets your facility’s demands.

Flow Rate and Pressure Dynamics

The most notable distinction between these pump styles lies in how they react to pressure. Positive displacement pumps maintain a constant output flow even when system backpressure fluctuates, making them indispensable for metering and dosing applications that demand total consistency.

Conversely, centrifugal pumps experience variable flow rates based on system resistance. As discharge pressure increases, output flow drops proportionally. This design works exceptionally well for high-volume applications where precise metering is less critical than moving fluid rapidly.

Efficiency and Energy Consumption

When evaluating energy performance, positive displacement pumps excel with thick or viscous fluids, maintaining high efficiency without losing flow capacity. However, pushing heavy materials under extreme pressure requires higher initial driving energy.

Centrifugal pumps deliver maximum energy efficiency when pumping low-viscosity liquids like water or thin chemicals. Their efficiency peaks at specific points along their operating curve; running a centrifugal pump too far off its efficiency center can trigger cavitation, vibration, and mechanical damage. Positive displacement pumps are far less sensitive to operating curve location and can run across variable pressures without efficiency degradation.

Inlet Conditions, Suction Lift, and Shearing

Standard centrifugal pumps must have fluid present in the housing to generate a pressure differential, making them incapable of self-priming unless equipped with specialized auxiliary chambers. High-speed impeller rotation can also cause fluid shear, which damages shear-sensitive products like emulsions or food gels.

Positive displacement pumps generate continuous negative pressure at the suction inlet, giving them natural self-priming capabilities and the ability to draw suction lift. Furthermore, because internal fluid movement is slow and smooth, they generate little internal shear, preserving the delicate characteristics of the material being pumped.

Which Pump Is Right for Your Business?

Determining whether a positive displacement pump or a centrifugal pump is right for your business comes down to fluid characteristics, required flow rates, pressure demands, and system layout. Complex facilities—such as chemical manufacturing, oil refineries, and food processing plants—frequently utilize a combination of both types to satisfy different parts of their production lines.

Choose a Positive Displacement Pump if:

Your production process requires precise, predictable, and continuous flow rates.
You are pumping high-viscosity materials (oils, paints, resins, heavy syrups) or abrasive slurries containing solids.
You require strong self-priming, suction lift capability, or must handle entrained gases safely.
Your product is shear-sensitive and must be handled gently without altering its physical consistency.

Choose a Centrifugal Pump if:

You need to transfer large volumes of thin, low-viscosity fluids (water, light fuels, solvents) quickly.
Your operating system experiences pressure fluctuations and does not require a strictly fixed output volume.
You prefer a simple, cost-effective pump design with fewer moving parts and minimal routine maintenance needs.

Quality Industrial Pumps and Services from C&B Equipment

Selecting the right pump for your facility is crucial to maximizing uptime, protecting product quality, and keeping operational costs low over time. Whether your application calls for a rugged positive displacement pump or a high-capacity centrifugal pump, making an informed choice ensures your business runs smoothly.

At C&B Equipment, we specialize in matching industrial operations with the exact pump systems they need. As a trusted distributor of industrial equipment—including pumps, blowers, air compressors, and custom skid packages—we back every sale with expert engineering guidance and full field service. Serving industrial clients across Kansas, Oklahoma, Missouri, Arkansas, and the Texas Panhandle, our factory-trained technicians provide complete diagnostic, maintenance, and repair services to keep your plant operating at peak efficiency.

Contact C&B Equipment today to speak with an equipment expert, select the ideal pump for your application, and keep your business running stronger and longer!

BLOG