The Difference Between Centrifugal and Positive Displacement Pumps: When to Use Each Type?

Centrifugal and positive displacement pumps are fundamental in many industrial and process applications. Each has unique characteristics that make them suitable for specific tasks. In this article, we’ll break down the key differences between the two types, highlight their components, and help you decide when to use each.

What Are Centrifugal Pumps?

Centrifugal pumps use kinetic energy to move fluid. They are commonly found in industries such as:

• Mining
• Petroleum refining
• Chemical production
• Wastewater treatment

How Do They Work?

Centrifugal pumps function by converting rotational energy, typically supplied by an electric motor, into fluid velocity. This is achieved via an impeller, which increases the velocity of the fluid, and a volute, which converts this velocity into pressure.

Key Components

1. Impeller: The heart of the pump that imparts velocity to the liquid.
2. Pump Shaft: Transfers power from the motor to the impeller.
3. Volute: Converts kinetic energy into pressure, allowing the liquid to move through the system.

Advantages of Centrifugal Pumps

• High flow rate: They handle large volumes of liquid efficiently.
• Continuous flow: Centrifugal pumps provide a steady, continuous flow without pulsation.
• Simple design: They are easier to maintain due to fewer moving parts.

Limitations

While centrifugal pumps are excellent for high-flow, low-pressure applications, their efficiency decreases with increased fluid viscosity or system pressure.

What Are Positive Displacement Pumps?

Positive displacement pumps (PD pumps) displace a fixed amount of liquid with each cycle, making them ideal for high-pressure and high-viscosity applications. These pumps are divided into two main types:

• Rotary (uses rotating gears or rotors)
• Reciprocating (uses a piston or plunger)

How Do They Work?

PD pumps move fluid by trapping a fixed volume in a chamber and forcing it through the system. Each rotation or stroke moves a consistent amount of liquid, making these pumps suitable for handling thicker fluids and high-pressure needs.

Key Components

1. Chamber: A space where liquid is trapped before being pushed into the system.
2. Check Valves: Ensure that liquid flows in the right direction during each cycle.

Advantages of Positive Displacement Pumps

• Handles high-viscosity fluids: PD pumps excel in pumping thick, viscous liquids.
• High pressure: They are ideal for applications requiring high pressure.

Limitations

PD pumps produce a pulsed flow, which can be undesirable in some applications, and may require additional equipment to smooth out the pressure variations.

Centrifugal vs Positive Displacement: Fundamental Differences

The core difference between centrifugal and positive displacement pumps is how they move liquid:

• Centrifugal pumps rely on velocity and pressure to move fluid, making them ideal for high-flow, low-viscosity applications.
• Positive displacement pumps move a set volume of fluid per cycle, which makes them better suited for high-viscosity fluids and higher-pressure systems.

When to Use Centrifugal Pumps

Centrifugal pumps are the right choice when:

• High flow rates are required.
• Fluids are low in viscosity (like water or thin oils).
• Continuous operation with minimal pressure fluctuations is needed.

They are often found in general industrial applications, water treatment, and chemical processing.

When to Use Positive Displacement Pumps

Positive displacement pumps should be used when:

• High pressure or high viscosity fluids need to be pumped.
• Applications involve pulsed flow requirements or long pipelines.
• Accuracy in fluid volume is critical.

These pumps are ideal for oil, syrup, or high-viscosity chemical applications, as well as in situations where precise dosing is required.

Conclusion

Both centrifugal and positive displacement pumps have essential roles in various industrial applications. Understanding their key differences helps in choosing the right pump for the job. Centrifugal pumps are best for high-flow, low-pressure systems, while positive displacement pumps excel in high-pressure, high-viscosity tasks.

For optimal performance, always consider the specific needs of your application, whether it’s fluid type, pressure, or flow rate, to determine the best pump type.

 For a deeper dive on pumps, check out the Pump Sizing & Modeling Piping Systems For Liquids Course