Positive displacement pumps are classified into various types based on their design and the method of displacement they employ to move the fluid. Each type has a unique mechanism that makes it suitable for specific applications. Here, we’ll explore some of the most common types:
Rotary Pumps: These pumps move fluid using a rotary mechanism. There are several subtypes under this category:
- Gear Pumps: Consist of two or more gears that mesh together. As the gears rotate, the fluid is trapped in the spaces between the teeth and transported from the inlet to the outlet. Gear pumps are known for their simplicity and effectiveness in handling viscous liquids.
- Screw Pumps: Feature one or more screws in the pump housing. As the screws rotate, the fluid moves along the screw threads from the inlet side to the discharge side. Screw pumps are used for a variety of applications, including oil and gas, and wastewater treatment.
- Lobe Pumps: Have two or more lobe rotors that rotate synchronously without touching each other. The lobes create expanding volume on the inlet side, allowing fluid to enter the pump and be captured between the lobes, which then transport it to the outlet.
Reciprocating Pumps: This type of pump utilizes a reciprocating mechanism to move fluid. Key subtypes include:
- Piston Pumps: Utilize a piston moving back and forth in a cylinder to draw in and then push out the fluid. They can handle a variety of fluids and are highly effective at high pressures.
- Diaphragm Pumps: Use a flexible diaphragm that moves back and forth to create a variable-volume chamber. These pumps are particularly useful in applications requiring a high level of cleanliness and chemical resistance.
Peristaltic Pumps: Also known as tube or hose pumps. These pumps contain fluid within a flexible tube or hose, which is fitted inside a circular pump casing. As the rotor turns, a part of the tube under compression closes (or occludes), which pushes the fluid through the tube.
| Type | Description | Common Applications |
|---|---|---|
| Gear Pumps | Meshing gears pump the fluid. | Hydraulic, Chemicals |
| Screw Pumps | Screws rotate to move the fluid. | Oil, Waste Water Treatment |
| Lobe Pumps | Rotating lobes transport fluid. | Food, Pharmaceuticals |
| Piston Pumps | Piston drives fluid through a cylinder. | Water, Oil, Paint |
| Diaphragm Pumps | Diaphragm’s back and forth motion moves the fluid. | Chemicals, Food Processing |
| Peristaltic Pumps | Compressing tube or hose moves the fluid. | Medical, Laboratory |
Each type of positive displacement pump serves different purposes and offers unique advantages, making them suitable for a wide range of industries and applications. Whether handling high-viscosity fluids or requiring precise volume control, there’s a positive displacement pump designed for the task.
Operating principles of positive displacement pumps
Positive displacement pumps operate on a fundamental principle where a specific amount of liquid is captured in a confined space and then forced to move to the discharge area, essentially displacing the fluid from one area to another without any variance in volume. This operation consists of several cycles of mechanical motions, which can vary based on the specific type of pump but typically involve expanding and contracting cavities.
Basic Operation Process: All positive displacement pumps begin their cycle by creating an expanding cavity on the intake side of the pump. This expansion allows the fluid to flow into the pump. Following this, the cavity diminishes as the moving component returns to its original position or completes a cycle. This reduction in cavity volume pushes the fluid out of the discharge side. To prevent backflow and maintain a consistent directional movement of the fluid, these pumps are equipped with check valves that only allow the fluid to move in the desired direction.
Critical Components: The operation of a positive displacement pump is contingent on a few critical components:
- Actuating Mechanism: This can be a rotor, a piston, a plunger, screws, gears, or lobes, depending on the type of pump.
- Valves: These may be ball, flap, or sliding-shoe type. Valves are crucial as they control the flow of the fluid, ensuring it moves in the correct direction.
- Casing: Houses the internal components of the pump and helps contain the pressure of the fluid being pumped.
- Seals and Gaskets: These prevent leakage of the fluid from the pump, maintaining efficiency and safety.
Role of Seals: Seals are particularly important in positive displacement pumps because they help maintain the integrity of the fluid being pumped. Without proper sealing, fluids that are hazardous, or under high pressure, could lead to significant safety issues and environmental concerns.
Pressure Buildup: A distinctive feature of positive displacement pumps is their ability to produce high pressure. The pressure in these pumps does not depend on the speed of the pump, which is a contrast to other types of pumps like centrifugal pumps. Instead, it relies on the total volume of the displaced fluid once all the cavities have been filled. This characteristic makes these pumps ideal for applications requiring precise volumetric flows and high pressures.
Phase Shift Mechanism: In pumps like rotary or screw types, the liquid moves along with the turning parts, creating what is known as a “phase shift”. This action transforms the fluid’s path from the inlet to the outlet side amidst the interlocking parts.
Understanding the Efficiency and Flow Regulation: The efficiency of a positive displacement pump is primarily influenced by its capability to minimize leakage and maintain volumetric flow rates. Adjusting the speed of the actuating mechanism typically regulates flow. This regulation is linear, meaning that a proportional increase or decrease in speed will correspondingly change the flow rate.
Each cycle of a positive displacement pump—a combination of cavity expansion, fluid intake, cavity contraction, and discharge—is executed smoothly and continuously under normal operational circumstances. This operational method ensures a steady and predictable flow that can be easily controlled and modulated as per requirements, reflecting the robustness and versatility of positive displacement pumps in a wide array of applications.
Applications and advantages of positive displacement pumps
Positive displacement pumps prove invaluable across numerous industries due to their specific capabilities and performance advantages. These pumps are essential in applications where precision and reliability are paramount, ranging from everyday consumer products manufacturing to the handling of hazardous chemicals in industrial settings.
Key Applications: Positive displacement pumps are versatile and can be tailored to meet the needs of diverse applications and industries including:
- Oil and Gas: These pumps are used for a variety of tasks such as transferring crude oil, injecting chemicals, and in processes requiring high-pressure outputs.
- Chemical Processing: Due to their ability to handle corrosive liquids, maintain flow rates, and ensure the safety of hazardous materials, they play a critical role in the chemical sector.
- Pharmaceuticals: Precision and contamination-free transfer of liquids are crucial in pharmaceutical manufacturing, making these pumps ideal for such environments.
- Food and Beverage: Employed in the hygienic processing of food and drink products, these pumps handle everything from thick pastes to delicate wines with equal efficiency.
- Agriculture: Used for irrigation, pesticide, and fertilizer applications, their robust nature ensures efficient fluid handling in various agricultural processes.
- Water Treatment: These pumps facilitate the movement of clean water, wastewater, and other treatment chemicals in water and wastewater treatment facilities.
Advantages of Positive Displacement Pumps: Aside from their broad application range, these pumps offer numerous advantages that make them preferable over other types of pumps:
- Efficiency: Able to handle highly viscous fluids with ease and minimal energy loss.
- Consistent Flow: They provide a steady and predictable flow regardless of the system pressure, ideal for processes requiring precise volumetric flows.
- High-Pressure Capabilities: Unlike centrifugal pumps, positive displacement pumps are effective in systems requiring high pressure because their output does not vary with changes in the discharge pressure.
- Suction Lift Capabilities: These pumps are capable of creating substantial suction lift, with some types capable of handling up to 8.8 meters (28.87 feet) of suction lift.
- Self-Priming: Many types of positive displacement pumps are self-priming, which makes them easy to start and operate under various conditions.
These attributes highlight why positive displacement pumps are integral to efficient operational practices in so many sectors, cementing their role in industries that depend on precise, reliable, and effective fluid handling. Whether transferring delicate ingredients in food production or managing aggressive chemicals in a safe manner, these pumps offer the necessary resilience and precision. Their ability to maintain consistent flow rates, pressure levels, and handle a variety of fluid types ensures that they meet the rigorous demands of modern industrial applications.