Positive Displacement Pump (PDP), also known as PD Pump, is a versatile and efficient pumping solution widely used in various industries. On this page, you will discover everything you need to know about positive displacement pumps - their advantages, working principles, and the different types available. Rely on Fluid-o-Tech and discover more!
On this page, you discover:
• What is a positive displacement pump?
• Wich are the positive displacement pump types?
• Fluid-o-Tech's Positive Displacement Pumps
A positive displacement pump, also known as a volumetric pump, moves fluid by trapping a fixed amount of it and displacing it into the pump's discharge pipe.
In technical documentation, the terms positive displacement pump, PD pump and PDP pump are commonly used interchangeably to describe this pump technology.
Unlike centrifugal pumps, which rely on impellers to generate flow, PD pumps use mechanical means to move the fluid. This design ensures a consistent flow rate with low pulsations, regardless of system pressure variations.
Positive displacement pumps operate based on the principle of creating and maintaining a fixed volume within the pump.
• The pump’s rotating or reciprocating mechanism creates a pressure differential
• This pressure difference opens the inlet valve, allowing fluid to enter the pump chamber
• As the rotating or reciprocating mechanism moves, the fluid is trapped within the chamber and transported to the discharge side
• The outlet valve opens, and the fluid is expelled into the discharge pipe
• The process repeats, maintaining a continuous flow of fluid
A positive displacement pump operates through a repetitive mechanical cycle in which a fixed volume of fluid is captured, isolated, and transferred from the suction side to the discharge side. Unlike dynamic pumps, flow generation depends on physical displacement rather than velocity.
During the suction phase, the movement of the pumping element creates an expanding volume inside the pumping chamber. This expansion generates a pressure drop that allows the fluid to enter the pump through the inlet port. Proper suction conditions are essential to ensure complete chamber filling and to prevent cavitation.
Once the chamber is filled, the fluid is mechanically isolated from the inlet. Sealing elements such as close internal clearances, vanes, diaphragms or elastomeric components prevent backflow while the pumping mechanism transports the trapped volume toward the discharge side.
As the chamber volume decreases, the fluid is forced out through the outlet port into the discharge line. The delivered flow rate is directly proportional to pump speed, enabling precise and repeatable flow control typical of a PD pump.
• Precise Flow Control – positive displacement pumps deliver a constant flow rate, making them ideal for applications requiring accurate dosing and metering
• High-Pressure Capability – PD pumps can generate high discharge pressures, enabling them to handle viscous liquids and overcome system resistance
• Self-Priming – these pumps can self-prime, drawing fluid into the pump without additional priming mechanisms
• Versatility – positive displacement pumps can handle a wide range of fluids, including corrosive, abrasive, or high-viscosity liquids
• High efficiency – PD pump technology ensures minimal energy waste during operation, even under variable pressure conditions
Are you interested in a positive displacement pump for your production process? Fluid-o-Tech is here for you!
1. High viscosity fluids – when viscosity exceeds 300 cSt, PD pumps maintain efficiency where others fail
2. Constant flow across variable pressures – stable flow rate despite pressure fluctuations
3. Variable viscosity handling – ideal for processes where viscosity changes during operation
4. Changing back pressure conditions – consistent performance even with variable system resistance
5. Precision metering – suitable for accurate dosing and flow regulation
6. Low flow requirements – excellent performance in low-volume applications
7. High discharge pressure – capable of operating at elevated pressures without efficiency loss
8. Shear-sensitive fluids – gentle pumping action suitable for emulsions and biological materials
|
Property |
Centrifugal Pump |
Positive Displacement Pump |
|
Effective viscosity range |
Efficiency decreases as viscosity increases (max ~200 cP) |
Efficiency improves as viscosity increases |
|
Pressure tolerance |
Flow varies with pressure changes; efficiency drops at high or low pressures |
Flow remains consistent regardless of pressure; efficiency increases with pressure |
|
Priming |
Required |
Not required |
|
Flow (at constant pressure) |
Steady/continuous |
Pulsating |
|
Shearing of sensitive fluids (emulsions, slurries, biological fluids, food) |
High-speed motor can damage shear-sensitive media |
Low internal velocity; ideal for shear-sensitive fluids |
First of all, it is important to know that, within the realm of positive displacement pumps, there exist two primary classifications: reciprocating and rotary displacement pumps
A reciprocating displacement pump is a positive displacement pump that uses reciprocating motion, typically driven by a piston or plunger, to create pressure and displace fluid. The pump's reciprocating action draws in fluid through an inlet valve and then forces it out through a discharge valve in a repetitive back-and-forth motion.
Here are the specific pumps included in this category:
• Diaphragm pumps- utilize a flexible diaphragm to displace and transfer fluids. It operates by cyclically flexing the diaphragm, creating suction and discharge strokes to move the fluid through the pump. The diaphragm acts as a barrier between the pumped fluid and the moving parts of the pump, providing a seal and preventing cross-contamination. These pumps are commonly used for applications that require gentle handling of fluids, as they can handle sensitive or abrasive liquids without damaging or contaminating them
• Flexible Impeller- this special pd pump is commonly used for pumping fluids with low to moderate viscosity. It consists of a rotating impeller with flexible vanes or blades made of materials such as rubber or thermoplastic elastomer that allow the vanes to bend and flex. This flexibility creates a seal against the pump housing, effectively trapping and displacing the fluid. When the impeller rotates, the flexible vanes expand and contract, drawing in fluid through the inlet and propelling it out through the outlet. This mechanism ensures a consistent flow and gentle handling of the fluid
• Peristaltic Pumps- operate by squeezing and releasing a flexible tube or hose to move fluids. It utilizes a rotating mechanism, typically consisting of rollers or lobes, to compress the tube, creating a series of isolated fluid pockets. As the mechanism rotates, the squeezed section of the tube moves along, pushing the fluid in the desired direction. This technology enables the continuous pumping of fluids without interruptions and with complete isolation between the pump and the fluid, eliminating any direct contact.
A rotary displacement pump is a PDP pump that utilizes a rotating mechanism, such as gears, lobes, or screws, to generate pressure and transport fluid. The rotating action of the pump creates chambers that trap and transport fluid from the inlet to the outlet, ensuring a consistent flow rate and precise fluid displacement.
This category includes four specific pumps:
• Rotary lobe pumps - consist of rotating lobes within a pump casing. The lobes create chambers that draw in fluid through an inlet port and push it out through a discharge port. The design of this pd pump ensures a steady flow without pulsations. The fixed clearance between the lobes and casing allows efficient fluid transfer without causing shear or damage, making it ideal for viscous and shear-sensitive liquids such as food products, slurries, and industrial fluids
• Screw pumps - are a type of positive displacement pump that utilizes an intermeshing screw and casing to transfer fluid. It operates by the rotational motion of the screw, which creates a sealed chamber between the screw threads and the pump casing. As the screw rotates, the fluid is trapped and carried along the length of the screw threads, ultimately being displaced from the inlet to the outlet of the pump
• Gear Pumps - are a type of positive displacement pump that uses meshing gears to transfer fluids. It consists of two interlocking gears, typically spur gears or helical gears, housed within a pump casing. As the gears rotate, fluid is trapped within the spaces between the gear teeth and the pump casing, creating a continuous flow. The operation of a gear pump relies on the principle of positive displacement, where a fixed volume of fluid is transferred with each revolution of the gears. This results in a steady and consistent flow rate, making gear pumps suitable for applications that require precise fluid delivery and dosing accuracy
• Rotary Vane Pumps - utilize rotating vanes or blades to create suction and generate fluid flow. They consist of a cylindrical rotor with multiple vanes inserted into radial slots. As the rotor rotates, the vanes slide in and out due to centrifugal force and contact with the pump casing. During the intake stage, the rotating vanes create expanding volumes that draw in fluid through the inlet. As the rotor continues to rotate, the vanes push the fluid toward the outlet, compressing it and generating pressure. Finally, the fluid is then discharged from the pump.
Types of positive displacement pumps
|
Type of PD Pump |
Application |
Features |
|
Piston pump |
Water – high pressure washing; other low viscosity liquids; oil production; paint spraying |
Reciprocating action with piston(s) sealed with o-rings |
|
Plunger pump |
Same as piston pump (typically for higher pressures) |
Reciprocating action with plunger(s) sealed with packing |
|
Diaphragm pump |
Metering or dispensing; spraying/cleaning; water treatment; paints, oils; corrosive liquids |
Sealless, self-priming, low flows, capable of high pressures |
|
Gear pump |
High-viscosity fluids in petrochemical, chemical, and food industries: oil, paints, foodstuffs |
Meshed gears provide rotary pumping action |
|
Lobe pump |
Chemical and food industries; sanitary, pharmaceutical, and biotech applications |
Low shear and wear; easy to clean or sterilize |
|
Screw pump |
Oil production, fuel transfer/injection; irrigation |
Fluid moves axially with minimal turbulence; supports high flow rates |
|
Vane pump |
Low-viscosity fluids; automotive transmissions; fuel systems; beverage dispensers |
Resistant to entrained solids; handles vane wear; variable output design |
Are you looking for a reliable positive displacement pump manufacturer?
Fluid-o-Tech offers a wide range of reliable and efficient positive displacement pumps for various industrial applications. With our expertise in pump manufacturing and dedication to quality, our PD pumps deliver exceptional performance, durability, and precision in fluid transfer processes.
Here are some of our best models:
The CO/MO 50-200 seriespositive displacement pump features a robust rotary vane design, available with brass or stainless steel housing. Equipped with 3/8” GAS or NPT ports and an internal relief valve, these pumps offer nominal flow rates ranging from 50 to 200 l/h at 1450 rpm. They can also operate at 1750 rpm, providing approximately 20% more capacity, up to a maximum of 76 GPH. With a maximum discharge pressure of 16 bar (230 psi), these compact pumps are designed for easy mounting on widely available NEMA 48Y motors using a v-band clamp and appropriate coupling. Ideal for various applications, this positive displacement pump ensures reliability and efficiency.
The PO 70-400 series rotary positive displacement pumps feature durable brass or stainless steel housings with 3/8” GAS or NPT ports and an internal relief valve for enhanced safety. These pumps offer nominal flow rates ranging from 70 to 400 l/h at 1450 rpm, with the capability to operate at 1725 rpm for an increased capacity of up to 530 l/h. With a maximum discharge pressure of 16 bar (230 psi), these rotary positive displacement pumps are highly efficient for various applications.
The MG series magnet drive gear pumps are compact, high-precision positive displacement pumps designed for advanced technology applications. Utilizing a magnet drive system, these pumps feature a completely sealed pump chamber, ensuring safe handling of a wide range of corrosive liquids. Constructed with AISI 316L stainless steel housing and internal metal parts, the gears and bushings are available in PEEK™ or PTFE™, with additional material options and driving magnets to suit specific needs. These pumps are NSF certified, making them suitable for potable water and fluids for human consumption. The MG series operates quietly and without pulsations, handling high-temperature fluids up to 120°C (248°F) with a low coefficient of expansion.
As a manufacturer of PD pumps, our offerings extend beyond off-the-shelf products. We provide an effective and high-quality customization service tailored to fulfill our customers' specific requirements.
First of all, we provide a technical blueprint outlining the structure and functionality of your PD pump. This blueprint adheres to the most rigorous standards and addresses our customers' exacting demands. Throughout the design phase, we meticulously select the most appropriate materials, resilient components, and cutting-edge technology.
Flow rate, differential pressure, viscosity, temperature, chemical compatibility, sealing technology and allowable pulsation.
For applications requiring accuracy, low flow rates or high-viscosity fluids, a rotary positive displacement pump or other PD pump configuration is often the preferred choice.
Never operate a positive displacement pump against a closed discharge valve. Proper suction conditions are essential to prevent cavitation and mechanical damage.
Pre-filtration, correct material selection and scheduled preventive maintenance improve long-term reliability and service life.
Real-World Applications
Positive displacement pumps ensure hygienic design, low shear and precise dosing for beverages, syrups and dairy products.
PD pump solutions handle high-viscosity fluids, operate at high pressures and ensure reliable performance in harsh environments.
Positive displacement pump technology provides accurate metering, chemical resistance and enhanced process safety.
Maintenance and Troubleshooting
Regular inspection of seals, lubrication systems and internal clearances is essential for reliable PD pump operation.
Wear, leakage, cavitation and performance drift can be mitigated through correct installation, operating conditions and preventive maintenance.
Take the next step into the world of positive displacement pumps with Fluid-o-Tech!
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