Positive Displacement Pumps - Common Types, How They Work

Most Common Types of Positive Displacement Pumps

Updated on July 14, 2023

A positive displacement pump is a crucial piece of equipment in various industrial settings, prized for its ability to deliver a consistent flow rate, even under high-pressure conditions. This type of pump operates on the principle of reciprocating rotary action combined with diaphragmatic action, which effectively moves and releases fluids within the pump housing during each cycle.

Notably, the positive displacement pump is designed to maintain a steady flow regardless of pressure variations. It is an essential tool in industries such as petroleum, gas, chemicals, food and beverages, and water treatment. The reliability and precision of a positive displacement pump in handling various fluid viscosities and pressures make it a cornerstone technology in these critical sectors.

Table of contents:

How Do Positive Displacement Pumps Work?

There are about 10 different positive displacement pumps, including peristaltic pumps and reciprocating positive displacement pumps. A positive displacement pump works using the vacuum generated through fluid insertion into a vacuum. Once a chamber fills with fluid, the pump rotates, increasing the pressure on its head of pressure. The fluid then passes through a port of discharge to the pipe.

All types of positive displacement pumps involve a mechanism that falls into two categories depending on the type of motion it utilizes. These two categories of pump movement types are called reciprocating and rotary.

Reciprocating Positive Displacement Pumps

A positive displacement reciprocating pump operates through the alternating motion of pistons, plungers (in the case of plunger pumps), or diaphragms, known as reciprocation. During the first stroke, the piston creates a vacuum, opening the outlet valve and closing the inlet. On the reverse stroke, pressure closes the inlet valve and opens the outlet, allowing fluid to exit the chamber. Examples include diaphragm, piston, peristaltic hose, helical rotor, rotary lobe, gear and rotary pumps.

Suction Phase: During the suction phase, the piston or plunger moves backward, enlarging the cylinder volume and reducing the fluid pressure inside the cylinder. This creates a partial vacuum, and fluid from the reservoir flows into the cylinder through the pump inlet valve due to atmospheric or upstream pressure pushing against the fluid.

Discharge Phase: When the piston or plunger moves forward, the cylinder’s volume decreases, and the pressure increases. This pressure pushes the fluid through the discharge valve into the delivery pipe.

The critical components of reciprocating pumps include:

Pump Cylinder: Houses the piston or plunger.

Piston/Plunger: The moving component that facilitates pumping to increase fluid pressure.

Inlet Valve: Allows fluid to enter the cylinder during the suction phase.

Outlet Valve: Allows fluid to leave the cylinder during the discharge phase.

Crank and Connecting Rod (in some designs): Converts the rotating motion of a motor into the reciprocating motion needed for pumping.

    Types of positive displacement reciprocating pumps

    A reciprocating pump is a specific category of positive displacement pump that functions by using a reciprocating motion to effectively displace fluid. 

    DAE reciprocating pumps

    DAE reciprocating pumps

    DAE reciprocating pumps

    Piston pump (axial piston pump)

    The mechanical system of a piston pump consists of circulating pistons inside cylinders with valves for both inlet and outlet ports. Upon suction, the piston expands the pump chamber inside. The pressure decreases with this action, and the cylinder hose on the piston pump opens up so fluid can pass through your intake. The piston presses the fluid onto the cylinder, which raises its pressure during the pump’s operation. The suction valves close, then open the release valve, pushing the fluid out.

    Applications: The piston pump is standard in agriculture (irrigation), water treatment, and industrial applications.

    Advantages: A piston pump can handle large volumes and a wide range of fluid viscosity.

    Plunger pump

    A plunger pump operates on principles similar to piston pumps but with different designs. Plunger pumps operate under extremely strong pressure and a high flow rate due to a strong plunger pump seal. These reciprocating pumps are used for various critical pump applications, including high-pressure water jetting and cleaning.

    The plunger pump is the oldest type of reciprocating pump currently in everyday use.

    Applications: Ideal for high-pressure applications such as oil and gas production, pressure cleaning, and dewatering.

    Advantages: High-pressure capability, durability, and efficiency with minimal leakage.

    Diaphragm Pump

    A diaphragm pump, or membrane pump, uses a flexible diaphragm that oscillates to change the volume of a chamber. This creates a vacuum that draws fluid in through an inlet valve. When the diaphragm contracts, it decreases the chamber volume and increases pressure, pushing the fluid out through the outlet valve.

    The diaphragm’s cyclical movement, driven mechanically by a crank or motor or actuated by compressed air, ensures continuous fluid flow with each stroke. Diaphragm pumps are handy for handling hazardous or corrosive fluids because the diaphragm and the pump body can be made of materials resistant to chemical attack. Meanwhile, air operated diaphragm pumps do have the ability to deal with various fluid viscosities.

    Additionally, these pumps are favored in applications requiring a hermetically sealed pump environment to avoid leaks and contamination. This makes the diaphragm pump ideal for use in industries like chemical manufacturing, pharmaceuticals, and water treatment.

    Applications: Diaphragm pumps are widely used for pumping hazardous and corrosive chemicals, preventing fluid contact with the pump’s mechanical parts.

    Advantages: A Diaphragm pump provides leak-free pumping action, can handle abrasive and corrosive fluids, and gently handle shear-sensitive fluids.

    What are the main features and benefits of a positive displacement pump?

    The pump family is divided into three parts: positive displacement, centrifugal and other. Centrifugal pumps can achieve excellent flow rates. In some chemical plants, 90% of pumps are centrifugal pumps. There are some uses for positive displacement pumps. The machines can also handle high-pressure fluids with relatively low flow rates. They can also provide greater accuracy if measurement is essential.

    High Efficiency: Capable of very high efficiencies, especially at high outlet pressure.

    Constant Flow Rate: The flow rate is almost independent of the pressure, making these pumps suitable for dosing and metering applications.

    Self-Priming: The ability to handle mixtures of air and fluid is helpful in applications where priming might otherwise be challenging.

    Reciprocating pumps are potent tools in industries where precision, high pressure, and reliability are crucial. Their design allows for versatile applications, from simple water transfer to handling complex and hazardous chemicals.

    Rotary positive displacement pumps

    Rotating positive displacement pumps use moving gears instead of the back-and-forth motion typical of reciprocating pumps. These pumps seal liquid within the casing, creating suction at the outlet. Fluids are transported through the casing by rotating gears or cylinders. Gear pumps, including internal and external types, are typical examples. External gear pumps feature interlocked gears on separate shafts or a single shaft, allowing for different driving configurations. Another type is the peristaltic pump. Peristaltic pumps compress and release a flexible hose or tube, creating a peristaltic pumping action that moves fluids through the tubing. This design of peristaltic pumps ensures that the fluid only contacts the tubing, making it ideal for sanitary applications.

    Suction Phase: As the rotary element (e.g., gears, lobes, or screws) begins to rotate, it creates an expanding volume of pumped fluid on the inlet side. This expansion lowers the pressure inside the pump chamber, causing fluid to flow into the pump to fill this space.

    Transfer Phase: The trapped fluid is carried from the inlet side to the pump’s discharge side by the rotating moving parts. During this phase, the fluid is isolated from the inlet and outlet, ensuring controlled movement through the pump casing.

    Discharge Phase: As the rotary element continues to rotate, the chamber volume decreases, compressing the fluid and increasing its pressure. This increased pressure forces the fluid out through the pump’s discharge port.

      Types of positive displacement rotary pumps

      Positive displacement rotary pumps utilize rotating mechanisms to displace fluid. These pumps trap fluid inside the pump casing. Then they move it from the intake to the discharge side due to their rotary motion.

        DAE rotary positive displacement pumps

        DAE rotary positive displacement pumps

        Gear Pump

        Gear pumps are rotary positive displacement pumps that operate by using two rotational gears in a pumping chamber. The rotating gear pushes the liquid into the pump’s discharge line. During rotation, the gears trap water inside the motor teeth and send it to the pump inside. The trapped fluid is then pulled in the direction the gears spin until it finally escapes from the other sides.

        There are two types of gear pumps: external gear pumps and internal gear pumps.

        External gear rotary positive displacement pumps consist of two interlocking gears supported by separate shafts (one or both of these shafts may be driven). The gears’ rotation traps the fluid between the teeth, moving it from the inlet to the discharge and around the casing.

        An internal gear pump operates with a larger external gear (rotor) and a smaller internal gear (idler). The idler gear, located inside the rotor, is supported by a shaft. In some designs, both gears are driven; in others, only the rotor is driven.

        A gear pump can discharge fluid in either direction, depending on the direction of the gear rotation.

        Applications: Gear pumps (both external and internal gear pumps) are widely used in chemical installations, oil, and automotive applications to handle fuel, lubricants, and polymers.

        Advantages: The external gear pump has a simple and compact design and efficient handling of highly viscous fluids.

        Screw Pumps

        Screw pumps consist of one or more screws (helical rotors) that, when rotated, engage closely within a cylindrical cavity. The rotation of these screws forms cavities that trap and move the fluid from the inlet to the outlet.

        Applications: It is useful in applications requiring smooth, pulsation-free pumping action, such as fuel oil transport, hydraulics, and the chemical and food processing industries.

        Advantages: High flow rates, quiet operation, and capability to handle both low and high viscosity fluids.

        Lobe Pumps

        Lobe pumps operate similarly to gear pumps, but instead of gears, they use lobed rotors that rotate against each other with a very small clearance. They are non-contacting and thus wear at a slower rate than rotary vane pumps. The lobes don’t touch each other, which minimizes damage to the pumped fluid, allowing for gentle handling.

        Applications: They are common in the pharmaceutical, food, and beverage industries due to their ability to handle larger solids and sensitive materials like food pastes and pharmaceutical agents.

        Advantages: Gentle handling of solids, easy to clean and maintain, suitable for sanitary applications.

        Vane Pumps

        Vane pumps feature a series of vanes in a rotor rotating inside a larger circular cavity. The vanes extend from the rotor and slide against the casing, forming pumping chambers. As the rotor turns, fluid is drawn into the chambers and forced out of the pump housing.

        Applications: It is often used in mid-pressure applications such as automotive steering and braking systems and in handling low-viscosity fluids like solvents and fuel oils.

        Advantages: Good at maintaining steady flow and minimizing pump slip despite changes in pressure, can adjust to varying operating conditions.

        Standard Features and Benefits of Rotary Pumps

        Smooth and Continuous Flow: The continuous motion of the rotating element provides a steady flow without pulsation.

        Versatility: Can handle a wide range of viscosities and materials.

        Compact Design: They are generally smaller and more compact than reciprocating pumps, making them suitable for installations with limited space.

          DAE rotary positive displacement pumps

          Types of positive displacement pumps

          Positive Displacement Pumps Applications

          Positive displacement pumps are used across various industries due to their ability to handle complex fluids and deliver precise flow rates. Here are some critical industrial applications:

          Oil and Gas Production: Positive displacement pumps transfer crude oil and natural gas from production sites to processing facilities. They are also utilized in injecting chemicals and dosing additives necessary for refining processes.

          Chemical Processing: These pumps are essential in the chemical industry for safely and accurately handling corrosive, viscous, or abrasive chemicals. They ensure precise dosing and metering in chemical reactions and processing.

          Food and Beverage: In the food and beverage industry, positive displacement pumps handle sensitive and highly viscous fluids such as syrups, oils, and pastes without damaging the product. They are also used for bottling and packaging operations.

          Pharmaceuticals: The pharmaceutical industry relies on these pumps for the hygienic and precise transfer of active ingredients, solvents, and other fluids critical in manufacturing medicines.

          Wastewater Treatment: Positive displacement pumps are used in wastewater treatment plants to transfer sludge, dose treatment chemicals, and handle thick or abrasive waste fluids.

          Agriculture: These pumps are employed for irrigation and spraying applications, helping to transport water and agricultural chemicals across vast farming landscapes efficiently.

          What is the difference between a positive displacement pump and a centrifugal pump?

          When selecting a pump for industrial applications, understanding the differences between a positive displacement pump and a centrifugal pump is crucial. Each type has distinct operational mechanisms and is suited for different comparisons of these two common pump types:

          Flow vs. Pressure: Centrifugal pumps provide a variable flow rate depending on the system pressure, whereas positive displacement pumps deliver a constant flow rate regardless of the system pressure.

          Efficiency with Viscous Fluids: Positive displacements pump work more efficiently with viscous fluids, while centrifugal pumps are more effective with low-viscosity fluids.

          Pulsation: Positive displacement pumps typically produce a pulsating flow due to their cyclic operation, whereas centrifugal pumps deliver a smooth and continuous flow, maintaining consistent pump speed.

          Priming: Centrifugal pumps generally require priming to begin operation as they cannot handle air pockets, whereas positive displacement pumps are self-priming and can handle air within the fluid.

          Complexity and Cost: Positive displacement pumps usually have more complex pump casings and are more expensive than centrifugal pumps due to their design and the precision required in manufacturing.

          Maintenance: Positive displacement pumps often require more maintenance because they have more moving parts and seals that are subject to wear.

          Operating Speed: Positive displacement pumps generally operate effectively at lower speeds than centrifugal pumps, which need higher pump speed to maintain the kinetic energy required for their operation.

          Pressure Generation: Positive displacement pumps can generate high pressures, making them suitable for applications requiring high pressures over a short distance, unlike centrifugal pumps, which are better suited for lower pressures over longer distances.

          Sealing: Positive displacement pumps can handle higher pressures, so they often require more robust pump casing sealing mechanisms to prevent leaks than the more straightforward pump casing seals often sufficient for centrifugal pumps.

          Handling Solids: Positive displacement pumps can handle fluids containing solids or slurries without impacting their operation. In contrast, centrifugal pumps are less tolerant of solids and can be damaged by them.

          Why choose DAE Pumps?

          DAE Pumps is a distinguished provider of positive displacement pumps, offering robust solutions across various industries, including oil and gas, chemicals, food and beverage, and wastewater treatment.

          Their positive displacement pumps are celebrated for maintaining a consistent flow rate even at high pressures, critically essential for reliable and efficient industrial operations.

          One key advantage of choosing DAE Pumps is its commitment to quality and innovation. The company uses high-quality materials to manufacture pumps that require minimal maintenance, reducing wear and tear.

          This commitment extends to its design philosophy, which integrates features to enhance the durability and functionality of the pumps, ensuring they meet the specific needs of different industrial applications.

          Furthermore, DAE Pumps proactively engages with customers to optimize their pump solutions. This customer-centric approach enhances the pumps’ performance and longevity and ensures they are well-suited to handle the demanding requirements of various sectors.

            Final words

            Positive displacement pumps are very helpful in any business that needs to move fluids efficiently and carefully, such as the oil and gas exploration, chemical processing, and water treatment industries.

            Some of the highlights that make them the workhorse in industries are:

            Consistent Flow Rates: Positive displacement pumps are ideal for applications requiring precise flow rates, such as oil and gas exploration, chemical processing, and water treatment, because they can deliver consistent flow regardless of pressure changes.

            Handling Complex Fluids: These pumps can handle viscous, abrasive, or corrosive fluids, making them suitable for industries that work with challenging materials without damaging equipment.

            Reliability and Durability: Positive displacement pumps are known for their reliability and durability. They minimize the risk of breakdowns and facilitate easy maintenance, which is crucial for maintaining continuous operations in critical industrial settings.

            Operational Efficiency: They ensure high uptime and reduced maintenance costs, which are essential in industries where prolonged downtimes can lead to significant financial losses.

            Versatility: Their robust design enables practical application performance, ensuring process reliability and quality control in various industrial environments.

            For the proper selection of positive displacement pumps for pulp and paper, sewage treatment, and mining industries, call DAE Pumps at (760) 477-4224. You can also contact us for a free sales quote.

              Frequently asked questions about positive displacement pumps

              1: What is the difference between positive displacement pumps and centrifugal pumps?

              Positive displacement pumps capture and displace a fixed amount of fluid, giving a consistent flow rate and high pressures. Centrifugal pumps generate large flows but low pressures. Centrifugal pumps are suited for high-flow pumping applications with low to moderate viscosity. Positive displacement pumps handle viscous fluids with precision.

              2: Can a positive displacement pump run dry?

              It is best to avoid letting a positive displacement pump run dry for an extended period of time. It can reduce the pump efficiency. In order to build a seal and generate the necessary hydraulic forces, the pumps require the presence of fluid. In addition to increasing friction, heat, and wear on components, running a positive displacement pump dry can also cause the seal to fail.

              3: Are positive displacement pumps suitable for handling abrasive fluids?

              Yes, these pumps are generally well-suited for handling abrasive fluids. Their design and operating principle make them suitable for transporting fluids containing solid particles or abrasive materials. To handle abrasive fluids, these pumps are designed to be robust and deliver non-impacting flow. 

              4: How do I do maintenance of positive displacement pumps for common problems?

              Check the power supply: Ensure that the pump is receiving proper electrical power or driver input.
              Inspect for leaks: Examine the pump and associated piping for any signs of leaks, such as fluid dripping or spraying.
              Monitor fluid levels: Low fluid levels can lead to poor performance or cavitation issues. Add fluid as needed, ensuring it is compatible with the pump and the application.

                Need Help?

                Our team of engineers is standing by to help you with your next project. Call us at (760) 821-8112 or submit a request.

                Need Help?

                Our team of engineers is standing by to help you with your next project. Call us at (760) 821-8112 or submit a request.