Positive Displacement Pumps March 1, 2024 Understanding Positive Displacement Pumps and Their Subtypes Positive displacement pumps are highly valued for their ability to deliver a consistent and precise flow of fluid regardless of variations in pressure, making them ideal for applications requiring accurate dosing, metering, and transfer. These pumps excel at handling viscous fluids, maintaining a fixed volume of fluid per revolution, and operating independently of outlet pressure, fluid properties, or inlet vacuum. Additionally, positive displacement pumps are self-priming, creating strong vacuums on the inlet side, which simplifies system design and eliminates the need for manual re-priming. DPP Centrifugal Versus Gear Pump Flow Rate Graph Positive displacement pumps can be divided into two subcategories. Each of these types operates differently and is suited for specific applications, depending on factors such as fluid properties, required flow precision, and system dynamics. Reciprocating Rotary Reciprocating Positive Displacement Pumps Reciprocating positive displacement pumps work through a linear back-and-forth movement, often referred to as a stroke. Each stroke results in the discharge of fluid, creating a pulsed flow profile. This can lead to vibration or potential hydraulic system damage, known as “water hammer.” Despite these challenges, reciprocating pumps are ideal for highly precise and repeatable fluid metering and dosing. Common types include: Diaphragm pump Piston pump Plunger pump Diaphragm Pump Diaphragm pumps use a flexible membrane to change the internal volume of the pump, allowing fluid to flow in and out. This type of pump is particularly effective for handling vacuum, air, and low-pressure corrosive fluids. Check Valve Examples in a Diaphragm Pump Piston Pump In piston pumps, a piston moves within a cylinder, expanding and contracting the volume of fluid within the pump. This action, combined with inlet and outlet valves, enables fluid movement. Piston pumps are known for their precision and reliability. DPP Diagram Piston Pump Valveless Piston Pump Valveless piston pumps operate without traditional valves, using a sinusoidal motion and piston rotation to open and close the inlet and outlet ports. This simplification reduces wear and maintenance, making them ideal for applications where valve failure could be problematic. DPP Valveless Piston Pump Plunger Pump Plunger pumps operate similarly to piston pumps but use a plunger instead of a piston to change the volume. This design also results in precise pumping action and is often used for high-pressure applications. DPP Diagram of Plunger Pump Rotary Positive Displacement Pumps Unlike reciprocating pumps, rotary positive displacement pumps use rotating elements to transfer fluid. These pumps provide smoother flow and are less prone to pulsed outputs, though they are typically less precise than reciprocating pumps. The most common types of rotary positive displacement pumps include: External gear pumps Internal gear pumps Vane pumps Peristaltic pumps Lobe pumps External Gear Gump External gear pumps are the simplest form of rotary pumps. Two gears, driven by a motor, trap fluid between their teeth and the pump casing, moving it from the inlet to the outlet. These pumps are widely used for their efficiency and straightforward design. DPP External Gear Pump Cycle Internal Gear Gump Internal gear pumps consist of two gears with different sizes and tooth counts. A crescent-shaped separator maintains a seal between the gears. While more complex than external gear pumps, they are ideal for specific applications where high power and precision are required. DPP Internal Gear Pump Gerotor Gerotor pumps are a specialized type of internal gear pump, operating without the crescent-shaped separator. They provide smooth and efficient pumping action but require high precision in manufacturing to maintain low clearances and optimal performance. DPP Diagram of Gerotor Pump Vane Pump Vane pumps use a single rotating element with vanes that slide or deform to maintain contact with the pump cavity. This design provides efficient flow even under pressure changes, though it can generate noise and cause wear over time due to sliding friction between the vanes and the pump housing. DPP Diagram of Vane Pump Peristaltic Pump Also known as roller pumps, peristaltic pumps move fluid through a flexible tube by compressing it with rotating rollers. Fluid only comes into contact with the inside of the tube, making these pumps ideal for sanitary applications such as dialysis machines. However, frequent tube replacement is often necessary due to wear from continuous compression. DPP Diagram of Peristaltic Pump Lobe Pump Lobe pumps resemble external gear pumps but feature lobe-shaped rotating elements instead of gears. These pumps can handle larger solid particles and are often used in applications requiring gentle fluid handling, such as in food and beverage processing. DPP Diagram of Lobe Pump Selecting the Right Pump for Your System Choosing the appropriate positive displacement pump is crucial to ensuring a stable and reliable hydraulic system. Collaboration with pump design engineers can help optimize performance, lifespan, and overall system efficiency. Whether you need precise metering with a reciprocating pump or a smoother flow with a rotary pump, selecting the right pump from the beginning will save time, effort, and resources. For expert guidance in selecting the ideal pump for your system, reach out to our pump design and engineering experts at Diener Precision Pumps, who are well-versed in delivering high-quality innovative solutions for a variety of fluid transfer applications.