With reference to hydraulic systems:
(a) state TWO functions of an accumulator;(2)
(b) describe, with the aid of a sketch, a gas charged diaphragm or bladder accumulator;(6)
(c) describe how the bladder is prevented from being extruded from the accumulator described in part (b).(2)
Question 4.
The question asks for a description of an accumulator, several give no description, many explain how it works – which is not asked for instead.
Hydraulic Accumulators
Hydraulic accumulators are versatile devices that perform several critical functions in hydraulic systems, making them invaluable components for various marine applications:
1. Energy Storage and Supply:
- Supplementing Pump Flow: During peak demand periods when the hydraulic system requires more flow than the pump can deliver, the accumulator releases stored fluid, supplementing the pump’s output. This prevents pressure drops and ensures smooth operation of actuators and other components. 1. Pulsation Dampening in a Hydraulic System with an Accumulator – Vissers Sales Corp. visserssales.com2. Benefits and Applications of Using a Hydraulic Accumulator in Industrial Systems www.micro-lube.com
- Emergency Power: In case of a pump failure or power outage, the stored energy in the accumulator can be used to maintain critical hydraulic functions, such as operating safety valves, emergency steering, or other vital systems. 1. Benefits and Applications of Using a Hydraulic Accumulator in Industrial Systems www.micro-lube.com
2. Pulsation Dampening:
- Smoothing Flow: Accumulators absorb pressure pulsations generated by pumps, especially positive displacement pumps. This helps to create a more constant and even flow of hydraulic fluid, reducing stress on components and improving system performance. 1. Top 5 Reasons to Use an Accumulator – Higginson Equipment www.higginson.ca
3. Maintaining Pressure:
- Leakage Compensation: In systems with minor leaks, the accumulator can release stored fluid to compensate for the gradual pressure loss, allowing the system to continue operating temporarily while the leak is addressed.
- Thermal Expansion: It accommodates changes in fluid volume due to thermal expansion, preventing excessive pressure buildup or vacuum within the system.
4. Shock Absorption:
- Sudden Pressure Surges: The accumulator acts as a shock absorber, absorbing sudden pressure spikes or surges that can occur when valves close quickly or loads change abruptly. This protects the system components from damage caused by these pressure transients. 1. Understanding the function of a hydraulic accumulator – Flowtech www.flowtech.co.uk
5. Auxiliary Power Source:
- Independent Operation: The accumulator can act as an independent power source for specific functions, such as operating emergency equipment or providing short bursts of high flow rates.
6. Energy Efficiency:
- Reduced Pump Size: By handling peak demands and storing energy, the accumulator allows for the use of a smaller pump, resulting in energy savings and reduced operating costs. 1. Operation of Hydraulic Accumulators for Energy Storage – comer-italia.com www.comer-italia.com
- Less Frequent Pump Cycling: The accumulator minimizes the frequency of pump starts and stops, reducing wear and tear on the pump and improving its overall efficiency.
Typical Applications on a Vessel:
- Emergency Steering: Providing backup hydraulic pressure for steering in case of a main system failure.
- Stabilizer Systems: Storing energy for rapid deployment and retraction of stabilizer fins.
- Deck Machinery: Supplying additional power for peak demands in winches, cranes, and other hydraulically operated equipment.
- Hydraulic Presses and Tools: Providing short bursts of high pressure for hydraulic presses, tools, and other applications.
In conclusion, hydraulic accumulators play a vital role in enhancing the performance, reliability, and safety of hydraulic systems on marine vessels. Their ability to store energy, dampen pulsations, maintain pressure, and provide emergency power makes them indispensable components in a wide range of onboard applications.
A gas-charged diaphragm or bladder accumulator
A gas-charged diaphragm or bladder accumulator is a type of hydraulic accumulator that stores potential energy in the form of compressed gas. It utilizes a flexible diaphragm or bladder to separate the gas from the hydraulic fluid, allowing for the storage and release of energy as the system pressure fluctuates.
1. What are Hydraulic Accumulators? – Control Gear
2. What Gas Is Used in Hydraulic Accumulators? – White House Products, Ltd
Key Components:
- Pressure Vessel (Shell): The main body of the accumulator, typically made of steel, designed to withstand high pressures. 1. What Are the Types of Accumulators? – VHS Hydraulics www.hydraulic-components.net
- Gas Chamber: A section within the pressure vessel filled with a compressible gas, usually nitrogen.
- Fluid Chamber: Another section within the vessel connected to the hydraulic system, filled with hydraulic fluid. 1. Hydraulic accumulator – Wikipedia en.wikipedia.org
- Separator: A flexible diaphragm or bladder that separates the gas and fluid chambers, preventing them from mixing while allowing for pressure transmission. 1. Diaphragm Accumulators – Hydac New Zealand www.hydac.co.nz
- Gas Valve: A valve for charging or discharging the gas in the gas chamber.
- Fluid Port: A connection point for the hydraulic fluid to enter and exit the accumulator. 1. Shop Accumulator Fluid Port Assemblies – OneHydraulics www.onehydraulics.com
Working Principle:
- Pre-charge: The gas chamber is pre-charged with nitrogen to a specific pressure, typically lower than the system’s minimum operating pressure. 1. Accumulator Basics – LunchBox Sessions www.lunchboxsessions.com
- Fluid Intake (Charging): When the hydraulic system pressure increases, fluid flows into the accumulator through the fluid port.
- Compression: The incoming fluid compresses the gas in the gas chamber, reducing its volume and storing potential energy.
- Fluid Discharge: When the system pressure drops, the compressed gas expands, pushing the diaphragm or bladder and forcing the stored fluid back into the hydraulic system.
Types:
- Bladder Accumulator: Uses a flexible rubber bladder to separate the gas and fluid. Offers fast response and good dirt tolerance but has a limited compression ratio. 1. Hydraulic accumulators – Issuu issuu.com2. Advice For Maintaining Hydraulic Accumulators – Machinery Lubrication www.machinerylubrication.com
- Diaphragm Accumulator: Employs a metal diaphragm for separation. Can handle higher pressures and is more compact but may have a slightly slower response time.
Functions in Hydraulic Systems:
- Energy Storage: Stores hydraulic energy during periods of low demand, releasing it during peak demand to supplement the pump’s output or provide temporary power during pump shutdowns. 1. Benefits and Applications of Using a Hydraulic Accumulator in Industrial Systems www.micro-lube.com
- Pulsation Dampening: Absorbs pressure pulsations from pumps, creating a smoother flow and reducing stress on system components.
- Shock Absorption: Dampens pressure spikes and surges caused by sudden changes in flow or load, protecting sensitive components.
- Leakage Compensation: Compensates for minor leaks in the system by maintaining pressure.
- Thermal Expansion Compensation: Accommodates changes in fluid volume due to temperature variations.
Advantages:
- Efficient Energy Storage: Stores and releases hydraulic energy effectively.
- Improved System Performance: Reduces pressure fluctuations, improves system responsiveness, and allows for smaller pumps.
- Increased Reliability: Provides backup power in case of pump failure or power outages. 1. Benefits and Applications of Using a Hydraulic Accumulator in Industrial Systems www.micro-lube.com
- Extended Component Life: Protects components from damage due to pressure spikes and pulsations.
Disadvantages:
- Requires Pre-charge: Needs to be pre-charged with gas to the correct pressure. 1. What Gas Is Used in Hydraulic Accumulators? – White House Products, Ltd www.whitehouseproductsltd.com
- Maintenance: Requires periodic inspection and maintenance to ensure proper function and gas pre-charge. 1. Advice For Maintaining Hydraulic Accumulators – Machinery Lubrication www.machinerylubrication.com
Overall, gas-charged diaphragm or bladder accumulators are valuable components in hydraulic systems, providing energy storage, pulsation dampening, shock absorption, and other functions that enhance system performance, reliability, and safety.
How the bladder is prevented from being extruded from the accumulator.
In a gas-charged bladder accumulator, preventing the bladder from being extruded (forced out) through the fluid port is crucial to maintain the integrity of the system and ensure its proper function. Here are the primary methods employed to achieve this:
- Poppet Valve:
- Function: This is a simple, spring-loaded valve located at the fluid port within the accumulator. It acts as a one-way valve, allowing fluid to flow into the accumulator but preventing it from flowing back out.
- Design: It typically consists of a disc or ball held against a seat by a spring. When the pressure in the fluid chamber is higher than the gas chamber, the poppet valve opens to allow fluid in. When the pressure reverses, the spring closes the valve, preventing the bladder from being pushed out.
- Effectiveness: This is a reliable and cost-effective method for preventing bladder extrusion in most applications.
- Anti-Extrusion Ring:
- Function: In some accumulators, an additional mechanical barrier called an anti-extrusion ring is used. It’s a ring-shaped component with an internal diameter slightly smaller than the fluid port, positioned between the bladder and the port.
- Design: It can be a fixed ring or a spring-loaded ring that exerts a force against the bladder, preventing it from extending past the port.
- Effectiveness: This provides an extra layer of protection, particularly in high-pressure applications or situations where there’s a risk of the poppet valve malfunctioning.
- Proper Pre-Charge Pressure:
- Function: Maintaining the correct pre-charge pressure in the gas chamber is also important in preventing bladder extrusion.
- Mechanism: The pre-charge pressure ensures that the gas pressure always exceeds the fluid pressure, even at the lowest system pressure. This prevents the bladder from collapsing completely and being forced out through the port.
- Operational Considerations:
- Avoidance of Full Discharge: It’s generally recommended to avoid completely discharging the fluid from the accumulator, as this can lead to the bladder collapsing and potentially being damaged by the anti-extrusion device or poppet valve. 1. Hydraulic Accumulator Failures and How to Prevent Them www.hydraulicsupermarket.com
- Proper Maintenance: Regular inspection and maintenance of the accumulator, including checking the poppet valve and anti-extrusion device (if present), are important to ensure they are functioning correctly and preventing bladder extrusion.
In Summary
Preventing bladder extrusion in gas-charged accumulators is achieved primarily through the use of a poppet valve and/or an anti-extrusion ring, along with maintaining the correct pre-charge pressure. These mechanisms act as safeguards, ensuring the bladder remains within the accumulator and the system operates safely and effectively.