A Complete Guide to Hydraulic Accumulator Types and How They Work
A Complete Guide to Hydraulic Accumulator Types and How They Work
Hydraulic accumulators are energy storage devices that allow hydraulic systems to operate at optimum levels. Hydraulic accumulators are used to maintain pressure, reduce pressure peaks, supplement pump flow and serve as power failure back-ups in hydraulic systems.
A variety of hydraulic accumulators are available. They include:
- Transfer barrier accumulators
- Bladder accumulators
- Piston accumulators
- Stainless steel accumulators
- Hydra cushions
- Diaphragm accumulators
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Hydraulic accumulator benefits
A hydraulic accumulator allows hydraulic systems to operate without the delays that may occur using a pump alone. They also help to increase the lifespan of hydraulic systems due to less pressure on components, such as seals and valves.
With regard to gas pressure, hydraulic accumulators store fluid that’s fed into the system when required. When pressure rises, the accumulator collects the fluid. In doing so, gas is compressed. Furthermore, when the pressure falls, compressed gas expands and pushes stored fluid into a hydraulic circuit.
As a safety feature, a hydraulic accumulator helps to eliminate delays due to a range of issues. For example, it ensures a hydraulic cylinder completes its stroke in the event of a failing pump. Most commonly, this is useful for applications that are subject to power failure and require a failsafe.
When using a hydraulic cylinder pump, a hydraulic accumulator reduces wear and tear for a cost-effective benefit. It ensures fast processes which make the system more environmentally friendly. As hydraulic fluid is released instantly with an accumulator, interruptions between the pump and the cylinder are avoided. Overall, these benefits ensure increased efficiency with regard to hydraulic systems.
A hydraulic accumulator ensures that a hydraulic system responds quickly to temporary actions and smooths out pulsations. As a pressure storage reservoir, it holds incompressible hydraulic fluid under pressure via an external source of energy, such as a spring, engine or compressed gas. Compressed gas accumulators are among the most commonly used.
Hydraulic accumulators store and discharge energy for the common use of improving the efficiency of hydraulic systems. In electrical systems, they are analogous to rechargeable batteries. Accumulators generally hold hydraulic fluid and compressible gas. Within the pressure vessel, a mobile barrier acts to separate the fluid from the gas. Stored energy in the compressed gas is released in order to force oil into a circuit from the hydraulic accumulator.
Before using a hydraulic accumulator, the gas volume must be pre-charged in order to expand gas volume and fill the accumulator with a small amount of oil. In terms of the minimum system working pressure, it should be at 80 to 90%. When it’s operating, a hydraulic pump raises system pressure. In turn, this pushes fluid into the accumulator via valves that control the flow. The accumulator bladder or piston compresses and moves gas volume when the fluid pressure overtakes the pre-charge pressure. This creates the energy source. When the gas pressures balance with the system, the action stops and the system restarts the charging cycle.
In order to supplement pump flow, along with decreasing pump capacity requirements, hydraulic accumulators store hydraulic fluid under pressure. Therefore, they minimise and maintain pressure and pressure fluctuations in closed systems. Hydraulic accumulators are also used in emergencies to provide auxiliary hydraulic power.
Similar to a battery that stores electrical energy, a hydraulic accumulator is a pressure vessel that stores hydraulic energy. It contains a piston or a bladder that traps and compresses inert gas, such as nitrogen. On the other side of the piston or bladder, an accumulator holds hydraulic fluid. The process begins with pre-charge pressure. When the system pressure overtakes the pre-charge pressure, the gas compresses and reduces in volume. Therefore, hydraulic fluid is allowed into the accumulator.
Following this, the fluid volume escalates until the system gets to its highest pressure. Then, the system pressure declines and the gas inflates. This pushes the fluid out of the hydraulic accumulator and gives power to the system. The end result is a pressure balance between the accumulator and the system. When used correctly, hydraulic accumulators ensure optimum efficiency. They’re cost-effective and offer failsafe protection. Lastly, hydraulic accumulators prolong the life of hydraulic system components.
Types of hydraulic accumulators
Hydraulic accumulators come in three common varieties: bladder, piston and hydraulic. As a general rule, bladder accumulators are the most popular all-purpose units as recommended by experts.
With big ports that allow for rapid fluid release, bladder accumulators are resistant to contamination due to dirt or other particles. They’re available in a large variety of sizes and they’re appropriate for shock applications. Generally, bladder accumulators are mounted vertically or on their sides when used for low-cycle applications. For the protection of the bladder due to material wear and tear, bladder accumulators are made with a 4:1 pressure ratio.
Piston accumulators feature separate fluid and gas sections with mobile pistons acting as the barrier between them. They’re often compared to hydraulic cylinders without rods. Another type of piston accumulator replaces high pressure gas with a spring in order to ensure force to the piston. The use of piston accumulators is for large stored volumes with high flow rates up to and more than 100 gallons.
Though piston accumulators are built for heavy-duty and industrial applications, they’re not recommended for shock applications. Furthermore, piston accumulators may not offer suitable resistance to contamination. If affected by contamination, damage could occur to system seals. In this event, seals can be replaced or repaired.
Diaphragm accumulators are very similar to bladder accumulators. However, diaphragm accumulators use an elastic diaphragm in the process of separating oil and gas volumes, rather than a rubber bladder. As they’re light and compact, diaphragm accumulators are economical. The small flow and volume offered is around one gallon.
Unlike a bladder, a diaphragm accumulator doesn’t significantly distort. This is because it’s capable of dealing with higher compression ratios of up to 8 to 10:1. In terms of mounting, diaphragm accumulators are flexible and also suitable for shock applications. This is due to the ability to respond quickly to pressure changes. As an extra benefit, diaphragm accumulators are resistant to contamination.
Hydraulic accumulators use dry nitrogen in the pre-charging process. This is used as it’s an inert gas that doesn’t react to external conditions that include pressurization, heat, compression or other chemicals. Nitrogen is the most cost-effective and the easiest gas to obtain. However, any inert gas is suitable for hydraulic accumulators.
It’s important to remember that oxygen or compressed air should never be used to charge a hydraulic accumulator. This is a fire hazard, as when oxygen is compressed and mixed with hydraulic oil it heats up and could cause an explosion. Depending on the manufacturer and the style, different charging assemblies are required. The charging assembly must match the hydraulic accumulator for safe use.