Difference between centrifugal and positive displacement pumps: technical guide to choosing

Difference between centrifugal and positive displacement pumps: technical guide to choosing

Continuity of the process, stability of performance, energy consumption, and final product quality are all aspects within a production plant that are influenced by the available technology and its specific use. Among the most common and commercially available technologies, Centrifugal pumps and positive displacement pumps represent two profoundly different solutions in terms of operating principle and application field. The former operate according to a dynamic logic, transferring energy to the fluid through the rotation of an impeller. The latter, on the other hand, work by positive displacement, trapping a defined volume of fluid and mechanically transferring it to the outlet.

This technical difference is then reflected in key parameters such as Flow rate, pressure, viscosity management, and adaptability to system variations. In some cases, therefore, the choice is immediate, while in others it requires a more articulated analysis that takes into account the real operating conditions, the hazardousness of the fluid to be moved, and the production sector in which the company operates.

For this reason, The design, selection, and maintenance of pumps should be addressed with an integrated approach. CDR Pompe It supports companies in understanding the real operating conditions, translating plant parameters and constraints into consistent and sustainable pumping solutions over time. The goal is to avoid standardized choices that do not take into account the actual behavior of the fluid and the process. From selection to operational management, support is built on the details that make a difference in daily operations.

Operating principle and characteristics of centrifugal pumps

Centrifugal pumps belong to the family of rotodynamic machines. This means that their operation is based on the rotation of an impeller, a component equipped with blades that transmits energy to the fluid.

The fluid enters the pump through the eye of the impeller and is accelerated radially outwards by centrifugal force. During this passage, the mechanical energy supplied by the motor is first transformed into kinetic energy and subsequently, within the pump casing, into pressure energy, and this transformation allows the fluid to be pushed along the discharge line.

One of the distinctive features of this type of pump is the continuity of the flowThe absence of separate suction and discharge cycles ensures smooth fluid handling, a fundamental characteristic in numerous industrial processes.

However, the pump's behavior is not isolated from the rest of the system. Every centrifugal pump is described by a characteristic curve that relates in relation to flow rate and total head, and the actual operating point is established by the interaction with the system curve. Even small variations in line resistances can therefore alter the operating point and, consequently, the actual performance of the system.

Operating principle and main technologies of positive displacement pumps

The Volumetric pumps operate on a different principle, namely they transfer fluid by moving defined volumes within a closed chamber. The cycle is driven by a mechanical movement, which can be reciprocating or rotary, and which allows the fluid to be drawn in and then pushed towards the discharge.

Each cycle therefore corresponds to a precise amount of fluid transferred. Consequently, the flow rate is directly proportional to the operating speed of the pump and remains substantially constant even as the pressure varies, within the design limits.

This feature makes positive displacement pumps suitable for applications where precise flow control is required, regardless of system conditions.

The main types of positive displacement pumps include:

• Diaphragm pump, used for aggressive or contamination-sensitive fluids. The fluid is separated from the mechanical components, reducing the risk of leakage or alteration.
• Gear pump, commonly used in industrial systems for handling viscous fluids such as oils and resins. The fluid is trapped between the gear teeth and transported along the housing.
• Screw pump, suitable for ensuring continuous and uniform flow even with high-viscosity fluids or those containing particles.

These are complemented by other solutions, such as lobe or piston pump, each designed for specific needs. The choice depends on the fluid characteristics and the required operating conditions.

Operational differences between centrifugal and positive displacement pumps

When comparing centrifugal and positive displacement pumps, the differences are especially apparent in their operating behavior.flow rate, pressure, fluid type, and response to system variations follow different logics and, consequently, analyzing these aspects allows us to understand which technology best suits the required operating conditions.

Flow rate and pressure response

One of the most relevant differences concerns the behavior of the flow rate in relation to the system pressure.

In centrifugal pumps, flow rate varies with back pressure: if the system resistance increases, the flow rate decreases; if it decreases, the flow rate increases. This behavior makes centrifugal pumps suitable for systems where a certain operational flexibility is required.

Positive displacement pumps, on the other hand, maintain an almost constant flow rate even when the pressure varies, up to the maximum limit for which they are designed. This stability allows for controlled process conditions, a useful feature in applications where precision is a requirement, such as’Pharmaceutical industry and chemistry.

From an engineering perspective, this difference means that, on one hand, we have a machine that adapts to the system, and on the other, a machine that imposes a defined flow rate and requires protection systems suited to its design requirements.

Fluid type and rheological behavior

The nature of the fluid (containing solids, corrosive, viscous) is perhaps the most determining factor in Pump selection and its materials and coatings. Centrifugal pumps, for example, work efficiently with low-viscosity fluids that are free of solid particles, like water, solvents, and light chemical solutions. This is because as viscosity increases, internal losses grow and efficiency drops significantly.

Volumetric pumps, on the other hand, are designed to handle viscous, dense, or non-Newtonian fluids. They can handle oils, sludges, paints, resins, and liquids containing suspended solids without compromising long-term performance.

This depends on their operating principle, as the fluid does not need to be “accelerated” but simply “displaced.” Consequently, resistances related to viscosity have a different impact compared to what happens in centrifugal pumps.

Generated pressure and performance

Centrifugal pumps are suitable for generating medium pressures, and the availability total head It depends on the pump configuration and the operating point along the characteristic curve.

Volumetric pumps, on the other hand, can reach high pressures even with relatively low flow rates., making them suitable for systems with high head loss, long lines, or processes that require constant thrust.

The choice between the two technologies, in this case, is often guided by required pressure level and the stability with which it must be maintained.

Energy efficiency and operating conditions

From an energy perspective, centrifugal pumps offer the best performance when operating near their best efficiency point., also known as BEP (Best Efficiency PointMoving away from this condition, efficiency decreases and mechanical stresses increase.

Volumetric pumps, on the other hand, exhibit more stable behavior: the yield tends to remain constant even when operating conditions vary, making them predictable in contexts where the plant load is nonlinear.

The energy assessment must therefore consider not only the nominal efficiency, but also the real conditions of use over time.

Application areas and strengths of centrifugal pumps

Centrifugal pumps they are widely used in many different sectors, and are among the most widespread technologies in the process industry thanks to their versatility, customization options, and compatibility with a long series of materials.

are particularly suitable, for example, for Transfer of water and low-viscosity fluids, both in the industrial sector and in auxiliary services. They are also used in the ilight chemical industry, in water treatment plants, in cooling circuits, and in all those processes that require high flow rates and continuous flows.

their spread is also linked to a combination of technical and economic factors The ratio of performance to cost is favorable, construction is relatively simple, and maintenance is accessible. Furthermore, modularity allows for the pump's configuration to be adapted to the specific needs of the system.

Application areas and process accuracy of positive displacement pumps

Positive displacement pumps, on the other hand, are used when fluid characteristics or process requirements demand tighter control.

They find application in the Handling of heavy oils, paints, resins, and high-viscosity chemicals. They are also used for sludges and liquids containing solids, applications for which a centrifugal pump would be inefficient or subject to accelerated wear.

In the food industry, they handle products such as honey, creams, and syrups., where it is necessary to preserve the fluid's structure and ensure uniform handling.

A particularly relevant area is that of dosing: In fact, the ability to deliver a constant flow rate allows for precise control over the quantity of product transferred, which is an essential aspect in many industrial processes.

Finally, integration with automation systems allows these pumps to be managed precisely and repeatably, improving the overall quality of the process.

Advantages and disadvantages compared

Evaluating a pump means not only fully understanding its theoretical operation but also considering how these technologies perform over time. Each pump offers specific advantages but also has limitations that become evident under certain operating conditions. Focusing on these aspects helps select the product that best integrates with the entire system.

Advantages of centrifugal pumps

Centrifugal pumps are widespread in many industrial settings due to a combination of simple construction and good performance under standard conditions. When the fluid and the system are within the correct parameters, they ensure stable operation and relatively simple management.

• High levels
  They are designed to move large volumes of fluid continuously, a characteristic useful in processes that require constant and uninterrupted transfers.
• Low costs
  The relatively simple structure impacts the initial cost, making them accessible even for large-scale applications.
• Simple maintenance
  The reduced number of wear parts simplifies maintenance and reduces downtime.
• Efficiency with low-viscosity fluids
  In the presence of low-viscosity liquids, such as water or light solutions, they achieve high efficiencies, especially near the optimal operating point.

Disadvantages of centrifugal pumps

The disadvantage is that the performance of centrifugal pumps is directly dependent on operating conditions. Consequently, when these deviate from the ideal conditions, limitations emerge that can impact the efficiency and lifespan of the components and materials they are made from.

• Viscosity sensitivity
  The increase in fluid viscosity results in a loss of efficiency and a reduction in effective flow rate.
• Limited pressure
  They are not suitable for generating high pressures, especially in standard configurations.
• Difficulty with suspended solids
  The presence of particles can cause wear, blockages, or loss of performance.
• Work point dependency
  If the pump operates away from its optimal point, vibrations, consumption, and mechanical stresses increase.

Advantages of positive displacement pumps

Volumetric pumps are designed to ensure control and stability even in complex operating conditions. Their structure makes them suitable for handling difficult fluids and maintaining consistent performance over time.

• Constant flow rate
  The amount of fluid transferred remains stable regardless of system pressure, within design limits.
• High blood pressure
  I am able to achieve high pressure values even with low flow rates.
• Management of viscous and complex fluids
  They can work with oils, resins, sludges, and non-Newtonian fluids without significant loss of performance.
• Precision in dosing processes
  They allow for precise control of the fluid amount moved, a fundamental requirement in many industrial applications.

Disadvantages of positive displacement pumps

Alongside their advantages, positive displacement pumps require more careful management, both during the design phase and during operation. Some aspects must be considered to avoid problems over time.

• Higher initial cost
  The greater construction complexity is reflected in the price compared to centrifugal pumps.
• Greater mechanical complexity
  The presence of components in direct contact with the fluid requires careful design.
• Need for security systems
  They must be equipped with pressure relief valves to prevent damage in case of line blockage.
• More complex maintenance
  Some components are subject to wear, especially in the presence of abrasive fluids or harsh conditions.

Technical criteria for selecting the most suitable pump

The main parameters that must be considered before installing a centrifugal or positive displacement pump include, as we have seen, the fluid type, viscosity, required flow rate, operating pressure, and process continuity.

The most frequent errors actually concern the underestimation of viscosity or the failure to consider variations in the system's load.. The presence of solids or the need for precise dosing can also guide the choice towards one specific technology over another.

A comprehensive technical assessment therefore makes it possible to identify the most suitable solution and avoid critical issues during the operational phase. In this context, the support of a specialized partner such as CDR Pompe makes it possible to translate process data into a reliable and sustainable configuration over time.

Beyond Differences: How to Find the Most Suitable Solution

The difference between centrifugal and positive displacement pumps lies in a few concrete elements: the way the fluid is moved, their response to system pressure, and their ability to handle different viscosities and operating conditions. The former work well when high flow rates and clean fluids are required, with logic tied to rotational speed and balance with the system. The latter follow a principle of volumetric displacement, ensuring constant flow rate, higher pressures, and greater reliability when the fluid is viscous, complex, or contains solids.

The choice between the two technologies therefore depends on the actual process, not on a general preference. Analyzing the fluid type, operating conditions, and required long-term stability is what allows us to avoid unsuitable or difficult-to-manage solutions in production.

CDR Pompe steps in precisely at this point: it supports companies not only with supply and installation, but above all during the selection phase, translating the system’s characteristics into a coherent technical choice. The’The goal is to build reliable pumping systems, calibrated to the process and designed to reduce corrective interventions and inefficiencies over time.

Contact us for a consultation and to learn about all our services support, sale and maintenance at the pumps mechanical seal and magnetic drive.

Frequently Asked Questions

What is the main difference between centrifugal pumps and volumetric pumps?

The difference concerns the way the fluid is moved. Centrifugal pumps are rotodynamic machines: they impeller accelerate the fluid and transform its kinetic energy into pressure, with continuous flow. Volumetric pumps move a defined volume of fluid in each cycle, so the flow rate rest remains almost constant as the pressure changes.

How does the flow rate flow rate of a centrifugal pump and a volumetric pump change when the pressure in the system increases?

In a centrifugal pump, it flow rate decreases if the resistance of the system increases and increases if it decreases, because the working point arises from the intersection of the pump curve and the system curve. A volumetric pump maintains a flow rate nearly constant value up to the design limit, but requires overpressure valves against line blocks.

Which pump should I choose for viscous fluids or fluids containing suspended solids?

For viscous, dense or solid-suspension fluids, volumetric pumps such as screw, gear or diaphragm pumps are more suitable. The fluid is moved and not accelerated, so viscosity has less impact. In a centrifuge, an increase in viscosity increases internal losses and lowers efficiency, while solids cause wear and clogging.

Do volumetric pumps consume more energy than centrifuges?

It depends on the actual conditions of use, not just the nominal performance. Centrifugal pumps are very efficient near the point of maximum efficiency (BEP), but away from it they lose performance and increase vibrations and stresses. Volumetric pumps have a more stable performance as the load varies and, with viscous fluids, they can be more efficient overall.

What are the advantages and disadvantages of centrifugal pumps compared to volumetric pumps?

Centrifugal pumps offer high flow rates, low initial cost, simple maintenance, and high efficiency with low-viscosity fluids such as water and light solutions. The limitations are sensitivity to viscosity, limited generated pressure, difficulty with suspended solids, and strong dependence on the working point.

What technical criteria are needed to choose between a centrifugal pump and a volumetric pump for a system industrial?

The main criteria are the type of fluid, viscosity, flow rate demand, operating pressure, and continuity of the process. Solid materials present and the need for precise dosing should also be considered. The most common errors are underestimating the viscosity and ignoring the load variations in the system, two factors that can guide the choice towards one or the other technology.