Aux 1 Unit 5 Q2

A positive displacement pump is a type of pump that operates by mechanically displacing a fixed volume of fluid with each cycle or rotation. This means that for every complete movement of its internal mechanism, the pump delivers a specific, predetermined amount of fluid, regardless of the pressure at the outlet.  

1. Useful information on positive displacement pumps – Michael-Smith-Engineers.co.uk

2. Hydraulic Pumps: How It Works

Key Characteristics:

• Fixed Displacement: The pump’s design ensures that a fixed volume of fluid is moved with each cycle, creating a consistent and predictable flow rate.   1. Useful information on positive displacement pumps – Michael-Smith-Engineers.co.uk www.michael-smith-engineers.co.uk
• High Pressure Capability: Positive displacement pumps can generate high pressures, making them suitable for applications where substantial force is required 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 can handle air and create a vacuum, allowing them to draw in the fluid from the source without the need for external priming.   1. useful information on self-priming pumps – Michael-Smith-Engineers.co.uk www.michael-smith-engineers.co.uk
• Handles Viscous Fluids: They are effective at pumping thick, viscous fluids, slurries, and fluids with entrained solids, which can be challenging for other pump types.   1. Useful information on positive displacement pumps – Michael-Smith-Engineers.co.uk www.michael-smith-engineers.co.uk
• Accurate Metering: Their consistent flow rate makes them suitable for precise dosing or metering applications.   1. Useful information on positive displacement pumps – Michael-Smith-Engineers.co.uk www.michael-smith-engineers.co.uk

Types:

• Reciprocating Pumps: Use a back-and-forth motion to displace fluid. Examples include piston pumps, diaphragm pumps, and plunger pumps.   1. Useful information on positive displacement pumps – Michael-Smith-Engineers.co.uk www.michael-smith-engineers.co.uk
• Rotary Pumps: Use rotating elements to displace fluid. Examples include gear pumps, lobe pumps, screw pumps, vane pumps, and peristaltic pumps.   1. Useful information on positive displacement pumps – Michael-Smith-Engineers.co.uk www.michael-smith-engineers.co.uk

Working Principle:

The basic principle involves creating a cavity or chamber within the pump. This cavity is filled with fluid, sealed off, and then the fluid is mechanically forced out of the pump and into the discharge pipe. This cycle repeats, resulting in a continuous (albeit pulsating) flow of fluid.  

1. Useful information on positive displacement pumps – Michael-Smith-Engineers.co.uk

2. What Are Positive Displacement Pumps? – North Ridge Pumps

Advantages:

• High Pressure: Can generate significant pressure, making them suitable for demanding applications.   1. Positive Displacement Pumps – when to use them – Michael-Smith-Engineers.co.uk www.michael-smith-engineers.co.uk
• Self-Priming: Eliminates the need for manual priming, simplifying operation.   1. Self Priming vs. Non Self Priming Pumps: Which Is Right for You? – Iwaki America Inc. iwakiamerica.com
• Handles Viscous Fluids: Efficiently handles a wide range of fluid viscosities, including thick and non-Newtonian fluids.   1. Useful information on positive displacement pumps – Michael-Smith-Engineers.co.uk www.michael-smith-engineers.co.uk
• Accurate Metering: Delivers precise and consistent flow rates, essential for dosing and metering applications.   1. Useful information on positive displacement pumps – Michael-Smith-Engineers.co.uk www.michael-smith-engineers.co.uk

Disadvantages:

• Pulsating Flow: The flow is not perfectly smooth but rather pulsating due to the cyclic nature of operation. This may necessitate the use of pulsation dampeners in some applications.   1. Useful information on positive displacement pumps – Michael-Smith-Engineers.co.uk www.michael-smith-engineers.co.uk2. Why Your Positive Displacement Pump System Needs a Pulsation Dampener – Blacoh www.blacoh.com
• Complexity and Maintenance: They tend to have more moving parts and a more complex design than other pump types, potentially leading to increased maintenance requirements.   1. Positive Displacement Pumps vs Other Common Pump Types: A Comparison nicholsportland.com
• Sensitivity to Blockages: A blockage in the discharge line can cause a rapid pressure increase, which can damage the pump or system. Relief valves are typically needed for protection.

Common Applications:

• Oil and Gas Industry: Transporting crude oil, refined products, and liquefied gases.   1. Positive Displacement Pumps for the Oil & Gas Industry | IDEX India www.idexindia.in
• Chemical Processing: Handling various chemicals, including corrosive and abrasive ones.   1. The Role of Positive Displacement Pumps in Chemical Industry – Iwaki America Inc. iwakiamerica.com
• Food and Beverage Industry: Transferring delicate and viscous food products.   1. Positive Displacement Pumps – Common Types, How They Work – DAE Pumps www.daepumps.com
• Pharmaceutical Industry: Dosing and metering precise amounts of ingredients.
• Marine Applications: Used for bilge pumping, fuel transfer, hydraulic systems, and other onboard systems.   1. Positive Displacement Pumps | SESINOKS sesinoks.com.tr

In essence: Positive displacement pumps offer distinct advantages in specific applications where high pressures, viscous fluids, self-priming capability, and precise metering are required.

Positive displacement pumps require relief valves primarily because of their inherent characteristic of generating a continuous flow at a relatively constant rate, regardless of the discharge pressure.  

1. Pressure Relief Valves for Positive Displacement Pumps

Here’s why this necessitates a relief valve:

1. Potential for Overpressure:

• Closed Discharge: If the discharge valve is closed or the system becomes blocked, a positive displacement pump will continue to try to deliver fluid, leading to a rapid buildup of pressure within the pump and piping.   1. Positive displacement pumps – Michael-Smith-Engineers.co.uk www.michael-smith-engineers.co.uk
• System Damage: Without a relief valve, this excessive pressure can cause catastrophic damage to the pump, pipes, valves, and other components, potentially leading to leaks, ruptures, and even explosions.

2. Protection of Pump and System:

• Pressure Limitation: A relief valve acts as a safety device by opening at a predetermined pressure setpoint, allowing excess fluid to bypass back to the suction side or a safe discharge location.   1. The Basics of Pressure Relief Valves – Beswick Engineering www.beswick.com
• Damage Prevention: This prevents pressure from exceeding the system’s design limits, protecting the pump, motor, piping, and other components from damage.   1. Pressure Relief Valves for Positive Displacement Pumps www.pumpsandsystems.com

3. Operational Safety:

• Preventing Accidents: By limiting pressure, relief valves help prevent accidents and injuries that could result from system overpressure and component failure.

4. Operational Flexibility:

• Process Control: In some applications, relief valves can be used to regulate pressure within a certain range, providing additional control over the process.

In Summary:

Positive displacement pumps, due to their constant flow characteristic, can create dangerous overpressure situations if the discharge flow is restricted or blocked. A relief valve is a crucial safety component that protects the pump, system, and personnel by preventing excessive pressure buildup and ensuring safe operation.  

1. Positive displacement pumps – Michael-Smith-Engineers.co.uk

2. Pressure Relief Valves for Positive Displacement Pumps

Relief valves on a vessel are strategically placed at critical points in systems prone to pressure buildup. On a superyacht, you’re likely to find them in these locations:

1. Engine Room & Machinery Spaces:

• Fuel Systems:
  • Downstream of fuel supply pumps to protect against overpressure that could damage pumps, filters, or piping.
  • On fuel oil heaters and purifiers to prevent excessive pressure buildup.
• Lubricating Oil Systems:
  • Downstream of lube oil pumps to protect against overpressure and maintain safe operating conditions for the engine.
• Hydraulic Systems:
  • On hydraulic power units and actuators to prevent damage due to pressure surges.
• Freshwater Systems:
  • On hot water calorifiers (heaters) or pressure tanks to prevent excessive pressure that could rupture the tanks or cause leaks.
• Compressed Air Systems:
  • On air compressors and receivers to protect against overpressure and potential explosions.
• Other Systems: Any other systems onboard that use pressurized fluids or gases, such as refrigeration systems or certain firefighting systems, may also have relief valves fitted.

2. Other Locations:

• Boiler:
  • Safety relief valves are essential components on boilers to prevent overpressure and potential explosions.
• Steering Gear:
  • Relief valves may be present in hydraulic steering systems to protect against pressure surges.
• Bilge System:
  • While less common, some bilge systems might have relief valves on the discharge side of the pump to prevent excessive pressure buildup if the discharge line becomes blocked.

Placement Considerations:

• Downstream of the Pump: Relief valves are typically installed downstream of the pump or pressure source to protect against excessive pressure generated by the pump.
• Accessibility for Maintenance: While ideally located in a protected area, relief valves should also be accessible for inspection, testing, and maintenance.
• Discharge Location: The discharge from the relief valve should be directed to a safe location where the released fluid or gas won’t cause harm or damage.

Remember: The specific location and number of relief valves will depend on the vessel’s design, the systems it has on board, and the applicable safety regulations and standards.

Key Takeaway: Relief valves are crucial safety components on vessels, protecting equipment, systems, and personnel from the dangers of overpressure. Understanding their typical locations on a superyacht is important for both operation and maintenance of these vessels.

A pulsation damper is fitted to the delivery line of a pump, typically a positive displacement pump, to address the issue of pulsating flow and the associated problems it can cause. Here are some specific scenarios where a pulsation damper would be beneficial on the delivery line:  

1. Pulsation Dampener Size, Location and Charge – Blacoh

1. Positive Displacement Pumps:

• Reciprocating Pumps: Pumps like piston pumps and diaphragm pumps inherently produce pulsating flow due to their reciprocating action. A pulsation damper on the delivery line significantly smooths out this flow, reducing pressure spikes and vibrations.   1. Why Your Positive Displacement Pump System Needs a Pulsation Dampener – Blacoh www.blacoh.com2. Item # A2MC1 2F8, Furon® A2 Pulsation Damper On Saint Gobain Performance Plastics cad.furon.com
• Rotary Pumps with High Pulsation: While some rotary pumps (e.g., gear pumps) have less pulsation than reciprocating types, they can still produce noticeable fluctuations in flow, especially at higher speeds or pressures. A damper can be used to further reduce these pulsations.

2. System Sensitivity to Pulsations:

• Sensitive Instruments: If the system includes flow meters, pressure sensors, or other sensitive instruments, pulsations can affect their accuracy and lifespan. A pulsation damper helps maintain a stable flow, ensuring accurate readings and protecting sensitive equipment.
• Piping and Equipment: Pressure fluctuations can cause stress and fatigue on pipes, fittings, and other system components. A damper minimizes these stresses, reducing the risk of leaks, vibrations, and premature wear.   1. How Fluctuating Pressure Occurs | ARD Vessels | Article and Information www.ardvessels.com
• Process Control: In applications requiring precise and consistent flow, such as chemical dosing or certain industrial processes, a pulsation damper can improve process control and efficiency.

3. Noise and Vibration Reduction:

• Noise: Pulsating flow can generate significant noise and vibration, especially in high-pressure systems. A pulsation damper helps dampen these vibrations and reduce noise levels, contributing to a more comfortable and quieter onboard environment.

4. Specific Operating Conditions:

• Long Discharge Lines: In systems with long discharge lines, pressure waves and reflections can amplify pulsations, making a damper even more crucial.
• High-Pressure Systems: Pulsations are more pronounced at higher pressures, so a damper becomes increasingly important in high-pressure systems.
• Variable Flow Rates: If the system experiences frequent changes in flow rate, a pulsation damper can help maintain a more stable and predictable flow, even during transitions.

In summary, a pulsation damper is recommended on the delivery line whenever pulsating flow from the pump is likely to cause problems like excessive vibration, noise, equipment wear, inaccurate measurements, or process disruptions. It’s particularly beneficial with positive displacement pumps and in high-pressure systems or those with sensitive instrumentation.

A pulsation damper works by utilizing a compressible medium, usually a gas like air or nitrogen, to absorb and release energy in response to pressure fluctuations in a fluid system, thus smoothing out the flow.

1. What is a Pulsation Dampener? – Yamada Pump

Key Components and their Functions:

• Chamber: A closed container, often cylindrical or spherical, that houses the compressible gas.
• Diaphragm or Bladder: A flexible membrane separates the gas chamber from the fluid flowing through the damper.
• Inlet and Outlet: Connections to the piping system allow the pulsating fluid to pass through the damper.

Operational Principle:

1. Pulsating Flow Enters:
   • The fluid with pressure variations (pulsations) enters the damper through the inlet.
2. Diaphragm/Bladder Compression (During Pressure Peak):
   • When the pressure in the fluid increases (a pressure peak or pulse), it exerts force on the diaphragm or bladder, compressing the gas inside the chamber.
   • This compression acts as an energy absorber, storing some of the excess energy from the pressure spike.   1. What Are Pulsation Dampeners & How Do They Work? – KNF knf.com
3. Energy Release (During Pressure Trough):
   • As the fluid pressure decreases (a pressure trough), the compressed gas in the chamber expands, pushing the diaphragm/bladder back.
   • This expansion releases the stored energy back into the fluid flow, filling in the pressure dip and smoothing out the flow.   1. What Are Pulsation Dampeners & How Do They Work? – KNF knf.com
4. Continuous Flow:
   • This cycle of compression and expansion repeats continuously in response to the pressure fluctuations, effectively dampening the pulsations and producing a more consistent flow at the outlet.

Benefits of Using a Pulsation Damper:

• Reduced Pulsation and Vibration: The primary benefit is the reduction of pressure fluctuations and vibrations in the system. This leads to:   1. What are pulsation dampers and how do they work? – Debem www.debem.com
  • Smoother, more consistent flow.   1. Pulsation Dampeners and Metering pumps – Milton Roy www.miltonroy.com
  • Reduced stress and wear on pipes, fittings, and other components.   1. What Is A Pulsation Dampener? – Technomax www.technomaxme.com
  • Improved accuracy of flow meters and other instruments.   1. Pulsation Dampeners and Metering pumps – Milton Roy www.miltonroy.com
• Improved Pump Efficiency: By creating a more stable flow environment, the pump operates more efficiently and with less strain.   1. What Are Pulsation Dampeners & How Do They Work? – KNF knf.com
• Extended Equipment Lifespan: Reduced stress on system components translates to longer equipment life and decreased maintenance costs.   1. What Are Pulsation Dampeners & How Do They Work? – KNF knf.com
• Noise Reduction: Dampening pulsations also helps to reduce noise generated by the system.   1. Pulsation Dampeners and Metering pumps – Milton Roy www.miltonroy.com

Types of Pulsation Dampers:

• Diaphragm Dampers: Use a flexible diaphragm to separate the gas and fluid chambers.
• Bladder Dampers: Utilize a bladder (similar to a balloon) inside the chamber to contain the gas.
• Piston Dampers: Employ a piston to separate the gas and fluid, often used in high-pressure applications.

Important Note:

• Correct Sizing: The damper must be appropriately sized based on system parameters like flow rate, pressure, and the degree of pulsation to be effective.   1. Sizing Pulsation Dampeners Is Critical to Effectiveness – Pumps & Systems www.pumpsandsystems.com
• Gas Pre-charge: The gas chamber is typically pre-charged with a specific gas pressure, which might require periodic adjustment.
• Maintenance: Regular inspections and maintenance are necessary to check for leaks, diaphragm/bladder integrity, and proper gas charge.

In essence, pulsation dampers act as shock absorbers for fluid systems, smoothing out the pressure waves and vibrations generated by positive displacement pumps or other sources of pulsating flow, leading to a more stable and efficient operation.  

1. Why pulsation dampeners matter – B2B Central