Hydraulic accumulators store pressurized fluid to act as a buffer during peak demand, pressure fluctuations, and hydraulic shocks. They allow for smaller pumps and protect against water hammer. Accumulators use external sources to maintain pressure and can use weights, springs, compressed gas, or metal bellows.
A hydraulic accumulator is a device that stores hydraulic pressure to act as a buffer in hydraulic systems during periods of peak demand, system pressure fluctuations, and to counteract hydraulic shocks. When the system is subjected to extreme loads, this pressurized fluid is introduced to relieve the demand on the hydraulic pump. This process is also repeated when there are unexpected drops in system pressure and when water hammer or hydraulic shock occurs. These devices use an external source to keep the fluid in the accumulator tank at approximately the same pressure as the average system pressure. There are several common types of hydraulic accumulator systems that use raised weights, springs, compressed gas, and metal bellows to maintain pressure in their reservoirs.
Using an externally pressurized source of buffer fluid in a hydraulic system allows designers to use smaller pumps than needed to handle peak demand. These conditions are commonly encountered in hydraulic systems such as those that power the undercarriage of large aircraft. An aircraft undercarriage cycle requires more hydraulic input than the rest of the systems collective average usage. In cases like these, hydraulic pumps can be rated for medium demand levels and be supplemented by accumulator pressure when needed. A hydraulic accumulator can provide much more pressurized fluid flow for a short time than the pump, making them ideal for high demand situations.
Even sudden pressure fluctuations in a hydraulic system can be handled by the pressure reserve in the accumulator. These fluctuations can be the result of environmental influences such as temperature changes or the result of slow leaks. A hydraulic accumulator can take up play, so to speak, and prevent the pump from consistently maintaining system pressure. This is particularly useful during low demand periods where system pressure only needs to be maintained at a pre-set level.
A hydraulic accumulator also adds an element of protection against aggressive hydraulic phenomena such as water hammer which can damage system components. Water hammer or fluid shock is a condition caused by a sudden change in direction or stoppage of moving hydraulic fluid. The resulting pressure wave can cause minor problems like shaking or noise in the system, or if severe enough, irreversibly damage system components. A hydraulic accumulator can form a barrier to protect the system from these pressure waves.
There are several methods used to maintain pressure in hydraulic accumulators, all of which are external and independent of system pressure. One of the oldest mechanisms in use is the weighted-up accumulator which relies on a weighted piston to maintain pressure in the tank. Other compression methods include pistons which rely on compressed gas or springs to maintain pressure in the accumulator. One of the most efficient types of accumulator is a variant that uses a hermetically sealed metal bellows arrangement instead of a piston to compress the fluid. This type of accumulator is particularly effective because it allows maximum flexibility in the type of fluid used and maximum storage volumes in the accumulator.
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