With reference to positive displacement pumps:
(a) describe, with the aid of a sketch, the operation of a pulsation damper;(6)
(b) explain why some positive displacement pump types do not require pulsation dampers.(4)
A positive displacement pump
A positive displacement pump is a type of pump that operates by mechanically displacing a fixed volume of fluid with each cycle or rotation. Unlike centrifugal pumps, which rely on centrifugal force to generate pressure, positive displacement pumps physically trap a specific amount of fluid and force it into the discharge pipe.
1. Useful information on positive displacement pumps – Michael-Smith-Engineers.co.uk
Key Characteristics:
- Fixed Displacement: They move a constant volume of fluid per revolution or cycle, regardless of the discharge pressure. 1. Positive displacement pumps, pump type – Diener Precision Pumps dienerprecisionpumps.com
- High Pressure Capability: They can generate high pressures, making them suitable for applications requiring significant force to move the fluid. 1. Useful information on positive displacement pumps – Michael-Smith-Engineers.co.uk www.michael-smith-engineers.co.uk
- Self-Priming: Most positive displacement pumps are self-priming, meaning they can pump air to expel it from the system and create a vacuum to draw in the fluid. 1. useful information on self-priming pumps – Michael-Smith-Engineers.co.uk www.michael-smith-engineers.co.uk
- Handles Viscous Fluids: They can efficiently handle viscous fluids, slurries, and fluids with entrained solids, which can be challenging for centrifugal pumps. 1. Useful information on positive displacement pumps – Michael-Smith-Engineers.co.uk www.michael-smith-engineers.co.uk
- Accurate Metering: They provide a consistent and predictable flow rate, making them suitable for applications requiring precise metering or dosing. 1. Useful information on positive displacement pumps – Michael-Smith-Engineers.co.uk www.michael-smith-engineers.co.uk
Types of Positive Displacement Pumps:
- Reciprocating:
- Rotary:
- Gear pumps 1. Overview Gear Pumps – Oberdorfer Pumps www.oberdorferpumps.com
- Lobe pumps 1. Lobe pump – Wikipedia en.wikipedia.org
- Screw pumps 1. Everything you need to know about screw pumps – Leybold www.leybold.com
- Vane pumps 1. Useful information on vane pumps – Michael-Smith-Engineers.co.uk www.michael-smith-engineers.co.uk
- Peristaltic pumps 1. Peristaltic pumps – how do they work? | Watson-Marlow | WMFTS www.wmfts.com
Working Principle:
The basic working principle involves the creation of a cavity or chamber within the pump. This cavity is then filled with fluid, sealed off, and the fluid is mechanically forced out of the pump and into the discharge pipe. This process is repeated in a cyclic manner, resulting in a continuous flow of fluid.
1. Useful information on positive displacement pumps – Michael-Smith-Engineers.co.uk
2. Positive Displacement Pump – Flexachem
Advantages:
- High Pressure: Can generate high pressures, suitable for applications requiring significant force to move the fluid. 1. Useful information on positive displacement pumps – Michael-Smith-Engineers.co.uk www.michael-smith-engineers.co.uk
- Self-Priming: Can pump air and don’t require priming, making them easier to start and operate. 1. Centrifugal vs. Positive Displacement Pump – Gainesville Industrial Electric www.gainesvilleindustrial.com
- Handles Viscous Fluids: Efficiently handles thick fluids, slurries, and fluids with entrained solids. 1. How Viscosity Can Impact Centrifugal and Positive Displacement Pumps – FCX Performance news.fcxperformance.com
- Accurate Metering: Provides a consistent and predictable flow rate, ideal for precise metering or dosing. 1. Useful information on positive displacement pumps – Michael-Smith-Engineers.co.uk www.michael-smith-engineers.co.uk
Disadvantages:
- Pulsating Flow: The flow from a positive displacement pump is pulsating rather than continuous, which may require additional dampening or smoothing in some applications. 1. Useful information on positive displacement pumps – Michael-Smith-Engineers.co.uk www.michael-smith-engineers.co.uk
- More Complex: They generally have a more complex design and more moving parts than centrifugal pumps, which can lead to higher maintenance requirements. 1. Useful information on positive displacement pumps – Michael-Smith-Engineers.co.uk www.michael-smith-engineers.co.uk
- Sensitive to Blockages: A blockage in the discharge line can cause a rapid pressure increase, potentially damaging the pump or system. Relief valves are often required for protection.
Applications:
- High-Viscosity Fluids: Pumping thick oils, slurries, pastes, and other viscous fluids. 1. Useful information on positive displacement pumps – Michael-Smith-Engineers.co.uk www.michael-smith-engineers.co.uk
- High-Pressure Applications: Systems requiring high discharge pressures, such as hydraulic systems or certain chemical processes.
- Precise Metering: Applications where accurate and consistent flow rates are needed, like chemical dosing or food processing.
- Self-Priming Requirement: Situations where priming is difficult or impractical, such as transferring fluids from underground tanks or remote locations.
In summary, positive displacement pumps are a versatile class of pumps that excel in handling high pressures, viscous fluids, and providing accurate metering. Their self-priming capability and ability to handle challenging fluids make them valuable in various industrial and marine applications.
1. Positive displacement pumps: efficiency & quality – kamat.de
How a pulsation damper operates to smooth out pulsating flow in fluid systems.
Core Principle
A pulsation damper essentially acts as an energy storage and release device. It absorbs the excess energy during pressure peaks (pulsations) and releases this stored energy during pressure troughs, resulting in a smoother, more continuous flow downstream.
1. What Are Pulsation Dampeners & How Do They Work? – KNF
Key Components:
- Chamber: A closed container, usually cylindrical or spherical, that holds a compressible medium (typically a gas like air or nitrogen).
- Diaphragm or Bladder: A flexible membrane that separates the gas chamber from the fluid flowing through the system. 1. What Is A Pulsation Dampener? – Technomax www.technomaxme.com
- Inlet and Outlet: Connections to the piping system, allowing the pulsating fluid to flow through the damper. 1. Components of Pulsation Dampeners – Red River www.redriver.team
Operation:
- Pulsating Flow Enters:
- The fluid with pressure fluctuations (pulsations) enters the damper through the inlet.
- Diaphragm/Bladder Compression:
- During a pressure peak, the increased fluid pressure pushes against the diaphragm or bladder, compressing the gas within the chamber.
- This compression absorbs and stores some of the excess energy from the pressure spike. 1. What Are Pulsation Dampeners & How Do They Work? – KNF knf.com
- Energy Release:
- During a pressure trough, the compressed gas in the chamber expands, pushing the diaphragm/bladder back and adding energy to the fluid flow.
- This helps fill in the pressure dip, smoothing out the flow.
- Continuous Flow:
- The damper continues to absorb and release energy in response to pressure fluctuations, effectively dampening the pulsations and producing a more consistent flow at the outlet. 1. What Are Pulsation Dampeners & How Do They Work? – KNF knf.com
Benefits of Pulsation Dampers
- Reduced Pulsation & Vibration: Minimizes pressure fluctuations, leading to smoother flow and reduced stress on pipes, fittings, and other system components. 1. What Are Pulsation Dampeners & How Do They Work? – KNF knf.com
- Improved Pump Efficiency: Reduces the workload on the pump by creating a more stable operating environment.
- Increased Equipment Lifespan: The reduced stress on system components translates to longer equipment life and lower maintenance costs. 1. What Are Pulsation Dampeners & How Do They Work? – KNF knf.com
- Reduced Noise: Dampening pulsations also reduces noise and vibration generated by the system. 1. What Are Pulsation Dampeners & How Do They Work? – KNF knf.com
- Improved Process Control: Consistent flow can improve the accuracy and efficiency of processes that rely on precise fluid delivery.
Applications on Superyachts:
- Positive Displacement Pumps: Commonly used with positive displacement pumps (like diaphragm or piston pumps), which inherently generate pulsating flow.
- Reciprocating Engines: Can be used to dampen pressure pulsations in fuel or cooling systems connected to reciprocating engines.
- Other Applications: May be used in any system where pulsation or vibration is a concern.
Types of Pulsation Dampers:
- Diaphragm Dampers: Use a flexible diaphragm to separate the gas and fluid chambers. 1. What is a Pulsation Dampener? – Yamada Pump www.yamadapump.com
- Bladder Dampers: Use a bladder (similar to a balloon) inside the chamber to store the gas.
- Piston Dampers: Utilize a piston to separate the gas and fluid, often used in high-pressure applications.
Important Considerations:
- Proper Sizing: The damper must be sized correctly based on the system’s flow rate, pressure, and pulsation characteristics to achieve optimal performance.
- Gas Precharge: The gas chamber needs to be precharged to a specific pressure, which might require periodic adjustment.
- Maintenance: Regular inspections and maintenance are needed to check for leaks, diaphragm/bladder integrity, and proper gas precharge.
Overall, pulsation dampers are vital components in systems with pulsating flow, contributing significantly to improved system performance, longevity, and safety.
Why some positive displacement pump types do not require pulsation dampers.
While pulsation dampers are commonly used with positive displacement pumps, some types inherently produce smoother flow, making the use of a damper less necessary. Let’s delve into the reasons behind this:
1. Pump Design and Operating Principle:
- Rotary Pumps with Multiple Displacing Elements: Rotary positive displacement pumps like screw pumps, lobe pumps, and multi-stage gear pumps have multiple rotating elements that work together to displace the fluid. This creates a more continuous flow compared to pumps with a single reciprocating piston or diaphragm, reducing the intensity of pulsations. 1. Rotary Lobe Pump: What Is It and How Does It Work? – Central States Industrial www.csidesigns.com
- Overlapping Displacement: In some rotary pumps, the displacing elements (lobes, screws, etc.) overlap during their rotation, creating a smoother transition between chambers and further minimizing pulsations.
- Progressive Cavity Pumps: These pumps use a single helical rotor rotating within a stator, creating a continuous flow with minimal pulsation. 1. A Comprehensive Guide to Progressive Cavity Pump www.globalpumps.com.au
2. System Requirements and Sensitivity:
- Tolerance for Pulsations: Some systems or processes may be less sensitive to pulsations, and the inherent smoothness of certain positive displacement pumps might be sufficient without additional dampening.
- Low-Pressure Systems: In low-pressure applications, the magnitude of pulsations is generally lower, reducing the need for a damper.
3. Cost and Complexity:
- Additional Component and Cost: Adding a pulsation damper increases the system’s complexity and cost. If the pump’s inherent pulsation level is acceptable for the application, omitting the damper can be a cost-effective solution.
4. Specific Examples of Pumps with Less Pulsation:
- Screw Pumps: The continuous meshing of the screws creates a smooth, nearly pulsation-free flow.
- Lobe Pumps: The multiple lobes and overlapping displacement reduce pulsations compared to single-piston or diaphragm pumps.
- Multi-Stage Gear Pumps: The multiple gears in these pumps contribute to a smoother flow compared to single-stage gear pumps.
- Progressive Cavity Pumps: The unique design of these pumps results in a continuous, low-pulsation flow.
When Pulsation Dampers are Still Recommended:
- Reciprocating Pumps: Single-acting or double-acting piston and diaphragm pumps typically exhibit significant pulsations and almost always benefit from pulsation dampers.
- High-Pressure Systems: Even with smoother pump designs, pulsations can be more pronounced at higher pressures, making dampers necessary to protect the system.
- Sensitive Equipment: If the system includes flow meters, control valves, or other sensitive components, a pulsation damper can be crucial to ensure their accuracy and longevity.
In conclusion, while pulsation dampers are commonly used with positive displacement pumps, some types, due to their design and operational characteristics, produce smoother flow, reducing the necessity of a damper in certain applications.
However, it’s important to consider the specific pump type, system requirements, and operating conditions to determine if a pulsation damper is needed to ensure optimal performance, protect system components, and reduce noise and vibration.